From 721d2547c6c2883b522740dc2b7ff420aeebb7e9 Mon Sep 17 00:00:00 2001
From: Kaloian Manassiev <kaloian.manassiev@mongodb.com>
Date: Fri, 2 Feb 2018 10:00:19 -0500
Subject: SERVER-29908 Move sharding_task_executor under mongo/s

---
 .../client/embedded/service_context_embedded.cpp   |   1 +
 .../db/auth/authz_manager_external_state_s.cpp     |   2 -
 src/mongo/db/auth/user_cache_invalidator_job.cpp   |   1 -
 src/mongo/db/catalog/collection_catalog_entry.h    |   1 +
 src/mongo/db/commands.h                            |   1 +
 src/mongo/db/db.cpp                                |   1 -
 src/mongo/db/index/index_descriptor.h              |   1 +
 src/mongo/db/index/sort_key_generator_test.cpp     |   2 +-
 src/mongo/db/keys_collection_client.h              |  10 +-
 src/mongo/db/keys_collection_client_direct.cpp     |  11 +-
 src/mongo/db/keys_collection_client_sharded.cpp    |   4 +-
 src/mongo/db/keys_collection_client_sharded.h      |   9 +-
 src/mongo/db/mongod_options.cpp                    |  19 +-
 src/mongo/db/query/parsed_distinct.cpp             |   1 +
 src/mongo/db/repl/topology_coordinator.cpp         |   5 +-
 src/mongo/db/s/SConscript                          |  15 +-
 src/mongo/db/s/balancer/balancer.cpp               |   1 -
 .../balancer_chunk_selection_policy_impl.cpp       |   1 -
 .../db/s/balancer/cluster_statistics_impl.cpp      |  19 +-
 src/mongo/db/s/balancer/migration_manager.cpp      |   2 +-
 src/mongo/db/s/balancer/migration_manager_test.cpp |   2 -
 .../db/s/balancer/scoped_migration_request.cpp     |  12 +-
 src/mongo/db/s/chunk_splitter.cpp                  |   1 -
 .../s/config/configsvr_drop_collection_command.cpp |   3 +-
 .../s/config/configsvr_drop_database_command.cpp   |   2 -
 .../db/s/config/configsvr_move_primary_command.cpp |   8 +-
 src/mongo/db/s/metadata_manager_test.cpp           |   1 -
 src/mongo/db/s/migration_source_manager.cpp        |   2 -
 src/mongo/db/s/sharding_task_executor.cpp          | 207 ---------------------
 src/mongo/db/s/sharding_task_executor.h            |  82 --------
 src/mongo/db/server_options.cpp                    |   2 +
 src/mongo/db/server_options.h                      |   1 -
 src/mongo/db/service_context_d.cpp                 |   1 +
 src/mongo/rpc/command_request.cpp                  |   1 +
 src/mongo/s/SConscript                             |  22 ++-
 .../s/catalog/sharding_catalog_client_impl.cpp     |   1 -
 src/mongo/s/catalog/sharding_catalog_client_mock.h |   1 -
 src/mongo/s/catalog_cache.cpp                      |   2 -
 src/mongo/s/client/version_manager.cpp             |   3 -
 src/mongo/s/commands/cluster_add_shard_cmd.cpp     |  29 +--
 .../s/commands/cluster_add_shard_to_zone_cmd.cpp   |  19 +-
 .../s/commands/cluster_enable_sharding_cmd.cpp     |  28 ++-
 .../s/commands/cluster_list_databases_cmd.cpp      |  45 ++---
 src/mongo/s/commands/cluster_list_shards_cmd.cpp   |   5 +-
 .../commands/cluster_user_management_commands.cpp  |   4 +-
 src/mongo/s/commands/cluster_write.cpp             |   1 -
 src/mongo/s/commands/commands_public.cpp           |   1 -
 src/mongo/s/grid.cpp                               |   3 -
 src/mongo/s/grid.h                                 |   4 +-
 src/mongo/s/server.cpp                             |  10 +-
 src/mongo/s/sharding_initialization.cpp            |   4 +-
 src/mongo/s/sharding_mongod_test_fixture.h         |  12 +-
 src/mongo/s/sharding_task_executor.cpp             | 207 +++++++++++++++++++++
 src/mongo/s/sharding_task_executor.h               |  82 ++++++++
 src/mongo/s/sharding_test_fixture.cpp              |   2 +-
 src/mongo/s/sharding_uptime_reporter.cpp           |   1 -
 src/mongo/transport/service_state_machine_test.cpp |   4 +-
 src/mongo/util/signal_handlers.cpp                 |   1 +
 58 files changed, 425 insertions(+), 498 deletions(-)
 delete mode 100644 src/mongo/db/s/sharding_task_executor.cpp
 delete mode 100644 src/mongo/db/s/sharding_task_executor.h
 create mode 100644 src/mongo/s/sharding_task_executor.cpp
 create mode 100644 src/mongo/s/sharding_task_executor.h

diff --git a/src/mongo/client/embedded/service_context_embedded.cpp b/src/mongo/client/embedded/service_context_embedded.cpp
index 4ab14c35152..597792a7846 100644
--- a/src/mongo/client/embedded/service_context_embedded.cpp
+++ b/src/mongo/client/embedded/service_context_embedded.cpp
@@ -36,6 +36,7 @@
 #include "mongo/client/embedded/service_entry_point_embedded.h"
 #include "mongo/db/client.h"
 #include "mongo/db/concurrency/lock_state.h"
+#include "mongo/db/operation_context.h"
 #include "mongo/db/storage/storage_engine.h"
 #include "mongo/db/storage/storage_engine_lock_file.h"
 #include "mongo/db/storage/storage_engine_metadata.h"
diff --git a/src/mongo/db/auth/authz_manager_external_state_s.cpp b/src/mongo/db/auth/authz_manager_external_state_s.cpp
index 2fb91f5b8ea..53700bb9ac9 100644
--- a/src/mongo/db/auth/authz_manager_external_state_s.cpp
+++ b/src/mongo/db/auth/authz_manager_external_state_s.cpp
@@ -44,14 +44,12 @@
 #include "mongo/db/jsobj.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/rpc/get_status_from_command_result.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/grid.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/mongoutils/str.h"
 #include "mongo/util/stringutils.h"
 
 namespace mongo {
-
 namespace {
 
 /**
diff --git a/src/mongo/db/auth/user_cache_invalidator_job.cpp b/src/mongo/db/auth/user_cache_invalidator_job.cpp
index 81602d77a14..8d6a690f19e 100644
--- a/src/mongo/db/auth/user_cache_invalidator_job.cpp
+++ b/src/mongo/db/auth/user_cache_invalidator_job.cpp
@@ -41,7 +41,6 @@
 #include "mongo/db/commands.h"
 #include "mongo/db/server_parameters.h"
 #include "mongo/rpc/get_status_from_command_result.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/grid.h"
 #include "mongo/stdx/mutex.h"
 #include "mongo/util/background.h"
diff --git a/src/mongo/db/catalog/collection_catalog_entry.h b/src/mongo/db/catalog/collection_catalog_entry.h
index 805bd130c46..ca07d2b17bc 100644
--- a/src/mongo/db/catalog/collection_catalog_entry.h
+++ b/src/mongo/db/catalog/collection_catalog_entry.h
@@ -40,6 +40,7 @@
 
 namespace mongo {
 
+class Collection;
 class IndexDescriptor;
 class OperationContext;
 
diff --git a/src/mongo/db/commands.h b/src/mongo/db/commands.h
index 7986cc6fe08..48cce22e3a6 100644
--- a/src/mongo/db/commands.h
+++ b/src/mongo/db/commands.h
@@ -41,6 +41,7 @@
 #include "mongo/db/commands/server_status_metric.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/db/query/explain.h"
+#include "mongo/db/repl/read_concern_args.h"
 #include "mongo/db/write_concern.h"
 #include "mongo/rpc/reply_builder_interface.h"
 #include "mongo/stdx/functional.h"
diff --git a/src/mongo/db/db.cpp b/src/mongo/db/db.cpp
index 14c628b5d35..19ffd88d700 100644
--- a/src/mongo/db/db.cpp
+++ b/src/mongo/db/db.cpp
@@ -110,7 +110,6 @@
 #include "mongo/db/s/sharding_initialization_mongod.h"
 #include "mongo/db/s/sharding_state.h"
 #include "mongo/db/s/sharding_state_recovery.h"
-#include "mongo/db/s/type_shard_identity.h"
 #include "mongo/db/server_options.h"
 #include "mongo/db/server_parameters.h"
 #include "mongo/db/service_context.h"
diff --git a/src/mongo/db/index/index_descriptor.h b/src/mongo/db/index/index_descriptor.h
index 5ba231f7664..3fae7128915 100644
--- a/src/mongo/db/index/index_descriptor.h
+++ b/src/mongo/db/index/index_descriptor.h
@@ -45,6 +45,7 @@ class Collection;
 class IndexCatalog;
 class IndexCatalogEntry;
 class IndexCatalogEntryContainer;
+class OperationContext;
 
 /**
  * A cache of information computed from the memory-mapped per-index data (OnDiskIndexData).
diff --git a/src/mongo/db/index/sort_key_generator_test.cpp b/src/mongo/db/index/sort_key_generator_test.cpp
index 854bb912f6e..f541919836d 100644
--- a/src/mongo/db/index/sort_key_generator_test.cpp
+++ b/src/mongo/db/index/sort_key_generator_test.cpp
@@ -28,8 +28,8 @@
 
 #include "mongo/platform/basic.h"
 
+#include "mongo/bson/json.h"
 #include "mongo/db/index/sort_key_generator.h"
-
 #include "mongo/db/query/collation/collator_interface_mock.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/unittest/death_test.h"
diff --git a/src/mongo/db/keys_collection_client.h b/src/mongo/db/keys_collection_client.h
index 4e93343ff3f..44cd5e2dd0b 100644
--- a/src/mongo/db/keys_collection_client.h
+++ b/src/mongo/db/keys_collection_client.h
@@ -28,17 +28,17 @@
 
 #pragma once
 
-#include <memory>
-#include <string>
+#include <vector>
 
-#include "mongo/base/status.h"
+#include "mongo/base/status_with.h"
+#include "mongo/base/string_data.h"
 #include "mongo/db/keys_collection_document.h"
 
 namespace mongo {
 
-class OperationContext;
-class LogicalTime;
 class BSONObj;
+class LogicalTime;
+class OperationContext;
 
 class KeysCollectionClient {
 public:
diff --git a/src/mongo/db/keys_collection_client_direct.cpp b/src/mongo/db/keys_collection_client_direct.cpp
index 4148b589bab..8ffc75f29ef 100644
--- a/src/mongo/db/keys_collection_client_direct.cpp
+++ b/src/mongo/db/keys_collection_client_direct.cpp
@@ -30,11 +30,11 @@
 
 #include "mongo/platform/basic.h"
 
+#include "mongo/db/keys_collection_client_direct.h"
+
 #include <boost/optional.hpp>
 #include <vector>
 
-#include "mongo/db/keys_collection_client_direct.h"
-
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/bson/util/bson_extract.h"
 #include "mongo/client/read_preference.h"
@@ -43,7 +43,6 @@
 #include "mongo/db/logical_clock.h"
 #include "mongo/db/logical_time.h"
 #include "mongo/db/operation_context.h"
-#include "mongo/db/server_options.h"
 #include "mongo/db/service_context.h"
 #include "mongo/rpc/get_status_from_command_result.h"
 #include "mongo/s/catalog/sharding_catalog_client.h"
@@ -52,8 +51,8 @@
 #include "mongo/util/log.h"
 
 namespace mongo {
-
 namespace {
+
 const int kOnErrorNumRetries = 3;
 
 bool isRetriableError(ErrorCodes::Error code, Shard::RetryPolicy options) {
@@ -68,7 +67,8 @@ bool isRetriableError(ErrorCodes::Error code, Shard::RetryPolicy options) {
         return false;
     }
 }
-}
+
+}  // namespace
 
 KeysCollectionClientDirect::KeysCollectionClientDirect() : _rsLocalClient() {}
 
@@ -165,4 +165,5 @@ Status KeysCollectionClientDirect::insertNewKey(OperationContext* opCtx, const B
     return _insert(
         opCtx, KeysCollectionDocument::ConfigNS, doc, ShardingCatalogClient::kMajorityWriteConcern);
 }
+
 }  // namespace mongo
diff --git a/src/mongo/db/keys_collection_client_sharded.cpp b/src/mongo/db/keys_collection_client_sharded.cpp
index 2f5bb8d6c9c..4b2cb51ce24 100644
--- a/src/mongo/db/keys_collection_client_sharded.cpp
+++ b/src/mongo/db/keys_collection_client_sharded.cpp
@@ -29,12 +29,11 @@
 #include "mongo/platform/basic.h"
 
 #include "mongo/db/keys_collection_client_sharded.h"
+
 #include "mongo/s/catalog/sharding_catalog_client.h"
 
 namespace mongo {
 
-namespace {}  // namespace
-
 KeysCollectionClientSharded::KeysCollectionClientSharded(ShardingCatalogClient* client)
     : _catalogClient(client) {}
 
@@ -50,4 +49,5 @@ Status KeysCollectionClientSharded::insertNewKey(OperationContext* opCtx, const
     return _catalogClient->insertConfigDocument(
         opCtx, KeysCollectionDocument::ConfigNS, doc, ShardingCatalogClient::kMajorityWriteConcern);
 }
+
 }  // namespace mongo
diff --git a/src/mongo/db/keys_collection_client_sharded.h b/src/mongo/db/keys_collection_client_sharded.h
index 2ced14f2135..b3f337e60ff 100644
--- a/src/mongo/db/keys_collection_client_sharded.h
+++ b/src/mongo/db/keys_collection_client_sharded.h
@@ -28,22 +28,16 @@
 
 #pragma once
 
-#include <memory>
-#include <string>
-
-#include "mongo/base/status.h"
 #include "mongo/db/keys_collection_client.h"
 
 namespace mongo {
 
-class OperationContext;
-class LogicalTime;
-class BSONObj;
 class ShardingCatalogClient;
 
 class KeysCollectionClientSharded : public KeysCollectionClient {
 public:
     KeysCollectionClientSharded(ShardingCatalogClient*);
+
     /**
      * Returns keys for the given purpose and with an expiresAt value greater than newerThanThis.
      */
@@ -62,4 +56,5 @@ public:
 private:
     ShardingCatalogClient* const _catalogClient;
 };
+
 }  // namespace mongo
diff --git a/src/mongo/db/mongod_options.cpp b/src/mongo/db/mongod_options.cpp
index 67b8b63545e..f77dce0fcc5 100644
--- a/src/mongo/db/mongod_options.cpp
+++ b/src/mongo/db/mongod_options.cpp
@@ -44,7 +44,6 @@
 #include "mongo/db/server_options.h"
 #include "mongo/db/server_options_helpers.h"
 #include "mongo/db/storage/mmap_v1/mmap_v1_options.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/util/log.h"
 #include "mongo/util/mongoutils/str.h"
 #include "mongo/util/net/ssl_options.h"
@@ -56,8 +55,6 @@ namespace mongo {
 
 using std::cout;
 using std::endl;
-using std::string;
-
 
 MongodGlobalParams mongodGlobalParams;
 
@@ -640,7 +637,7 @@ Status validateMongodOptions(const moe::Environment& params) {
 #ifdef _WIN32
     if (params.count("install") || params.count("reinstall")) {
         if (params.count("storage.dbPath") &&
-            !boost::filesystem::path(params["storage.dbPath"].as<string>()).is_absolute()) {
+            !boost::filesystem::path(params["storage.dbPath"].as<std::string>()).is_absolute()) {
             return Status(ErrorCodes::BadValue,
                           "dbPath requires an absolute file path with Windows services");
         }
@@ -943,12 +940,12 @@ Status storeMongodOptions(const moe::Environment& params) {
     }
 
     if (params.count("storage.engine")) {
-        storageGlobalParams.engine = params["storage.engine"].as<string>();
+        storageGlobalParams.engine = params["storage.engine"].as<std::string>();
         storageGlobalParams.engineSetByUser = true;
     }
 
     if (params.count("storage.dbPath")) {
-        storageGlobalParams.dbpath = params["storage.dbPath"].as<string>();
+        storageGlobalParams.dbpath = params["storage.dbPath"].as<std::string>();
         if (params.count("processManagement.fork") && storageGlobalParams.dbpath[0] != '/') {
             // we need to change dbpath if we fork since we change
             // cwd to "/"
@@ -1116,17 +1113,17 @@ Status storeMongodOptions(const moe::Environment& params) {
     }
     if (params.count("source")) {
         /* specifies what the source in local.sources should be */
-        replSettings.setSource(params["source"].as<string>().c_str());
+        replSettings.setSource(params["source"].as<std::string>().c_str());
     }
     if (params.count("pretouch")) {
         replSettings.setPretouch(params["pretouch"].as<int>());
     }
     if (params.count("replication.replSetName")) {
-        replSettings.setReplSetString(params["replication.replSetName"].as<string>().c_str());
+        replSettings.setReplSetString(params["replication.replSetName"].as<std::string>().c_str());
     }
     if (params.count("replication.replSet")) {
         /* seed list of hosts for the repl set */
-        replSettings.setReplSetString(params["replication.replSet"].as<string>().c_str());
+        replSettings.setReplSetString(params["replication.replSet"].as<std::string>().c_str());
     }
     if (params.count("replication.secondaryIndexPrefetch")) {
         replSettings.setPrefetchIndexMode(
@@ -1146,7 +1143,7 @@ Status storeMongodOptions(const moe::Environment& params) {
     }
 
     if (params.count("only")) {
-        replSettings.setOnly(params["only"].as<string>().c_str());
+        replSettings.setOnly(params["only"].as<std::string>().c_str());
     }
     if (params.count("storage.mmapv1.nsSize")) {
         int x = params["storage.mmapv1.nsSize"].as<int>();
@@ -1255,7 +1252,7 @@ Status storeMongodOptions(const moe::Environment& params) {
 
     // needs to be after things like --configsvr parsing, thus here.
     if (params.count("storage.repairPath")) {
-        storageGlobalParams.repairpath = params["storage.repairPath"].as<string>();
+        storageGlobalParams.repairpath = params["storage.repairPath"].as<std::string>();
         if (!storageGlobalParams.repairpath.size()) {
             return Status(ErrorCodes::BadValue, "repairpath is empty");
         }
diff --git a/src/mongo/db/query/parsed_distinct.cpp b/src/mongo/db/query/parsed_distinct.cpp
index 7fbb38648b2..8ff2277bee6 100644
--- a/src/mongo/db/query/parsed_distinct.cpp
+++ b/src/mongo/db/query/parsed_distinct.cpp
@@ -34,6 +34,7 @@
 #include "mongo/bson/util/bson_extract.h"
 #include "mongo/db/query/canonical_query.h"
 #include "mongo/db/query/query_request.h"
+#include "mongo/db/repl/read_concern_args.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/mongoutils/str.h"
 
diff --git a/src/mongo/db/repl/topology_coordinator.cpp b/src/mongo/db/repl/topology_coordinator.cpp
index 19c5293c0cc..e8b3710f283 100644
--- a/src/mongo/db/repl/topology_coordinator.cpp
+++ b/src/mongo/db/repl/topology_coordinator.cpp
@@ -35,6 +35,7 @@
 #include <limits>
 #include <string>
 
+#include "mongo/bson/simple_bsonobj_comparator.h"
 #include "mongo/db/audit.h"
 #include "mongo/db/client.h"
 #include "mongo/db/mongod_options.h"
@@ -62,7 +63,7 @@
 
 namespace mongo {
 namespace repl {
-using std::vector;
+
 const Seconds TopologyCoordinator::VoteLease::leaseTime = Seconds(30);
 
 // Controls how caught up in replication a secondary with higher priority than the current primary
@@ -1995,7 +1996,7 @@ void TopologyCoordinator::prepareStatusResponse(const ReplSetStatusArgs& rsStatu
                                                 BSONObjBuilder* response,
                                                 Status* result) {
     // output for each member
-    vector<BSONObj> membersOut;
+    std::vector<BSONObj> membersOut;
     const MemberState myState = getMemberState();
     const Date_t now = rsStatusArgs.now;
     const OpTime lastOpApplied = getMyLastAppliedOpTime();
diff --git a/src/mongo/db/s/SConscript b/src/mongo/db/s/SConscript
index b5c82cdae1d..fd53ece397b 100644
--- a/src/mongo/db/s/SConscript
+++ b/src/mongo/db/s/SConscript
@@ -19,19 +19,6 @@ env.Library(
     ],
 )
 
-env.Library(
-    target='sharding_task_executor',
-    source=[
-        'sharding_task_executor.cpp',
-    ],
-    LIBDEPS=[
-        '$BUILD_DIR/mongo/base',
-        '$BUILD_DIR/mongo/executor/thread_pool_task_executor',
-        '$BUILD_DIR/mongo/s/client/sharding_client',
-        '$BUILD_DIR/mongo/s/cluster_last_error_info',
-    ],
-)
-
 env.Library(
     target='migration_types',
     source=[
@@ -106,11 +93,11 @@ env.Library(
         '$BUILD_DIR/mongo/s/coreshard',
         '$BUILD_DIR/mongo/s/is_mongos',
         '$BUILD_DIR/mongo/s/sharding_initialization',
+        '$BUILD_DIR/mongo/s/sharding_task_executor',
         '$BUILD_DIR/mongo/util/elapsed_tracker',
         'balancer',
         'collection_metadata',
         'migration_types',
-        'sharding_task_executor',
         'type_shard_identity',
     ],
     LIBDEPS_TAGS=[
diff --git a/src/mongo/db/s/balancer/balancer.cpp b/src/mongo/db/s/balancer/balancer.cpp
index d537260c666..4b6c79c343c 100644
--- a/src/mongo/db/s/balancer/balancer.cpp
+++ b/src/mongo/db/s/balancer/balancer.cpp
@@ -44,7 +44,6 @@
 #include "mongo/db/s/balancer/balancer_chunk_selection_policy_impl.h"
 #include "mongo/db/s/balancer/cluster_statistics_impl.h"
 #include "mongo/s/balancer_configuration.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_chunk.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/client/shard_registry.h"
diff --git a/src/mongo/db/s/balancer/balancer_chunk_selection_policy_impl.cpp b/src/mongo/db/s/balancer/balancer_chunk_selection_policy_impl.cpp
index 5e89baca4e1..499c7605924 100644
--- a/src/mongo/db/s/balancer/balancer_chunk_selection_policy_impl.cpp
+++ b/src/mongo/db/s/balancer/balancer_chunk_selection_policy_impl.cpp
@@ -36,7 +36,6 @@
 
 #include "mongo/base/status_with.h"
 #include "mongo/bson/bsonobj_comparator_interface.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_chunk.h"
 #include "mongo/s/catalog/type_collection.h"
 #include "mongo/s/catalog/type_tags.h"
diff --git a/src/mongo/db/s/balancer/cluster_statistics_impl.cpp b/src/mongo/db/s/balancer/cluster_statistics_impl.cpp
index f0f50c1c09f..c23b6b41e32 100644
--- a/src/mongo/db/s/balancer/cluster_statistics_impl.cpp
+++ b/src/mongo/db/s/balancer/cluster_statistics_impl.cpp
@@ -35,7 +35,6 @@
 #include "mongo/base/status_with.h"
 #include "mongo/bson/util/bson_extract.h"
 #include "mongo/client/read_preference.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_shard.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
@@ -44,10 +43,6 @@
 #include "mongo/util/mongoutils/str.h"
 
 namespace mongo {
-
-using std::string;
-using std::vector;
-
 namespace {
 
 const char kVersionField[] = "version";
@@ -60,7 +55,7 @@ const char kVersionField[] = "version";
  *  ShardNotFound if shard by that id is not available on the registry
  *  NoSuchKey if the version could not be retrieved
  */
-StatusWith<string> retrieveShardMongoDVersion(OperationContext* opCtx, ShardId shardId) {
+StatusWith<std::string> retrieveShardMongoDVersion(OperationContext* opCtx, ShardId shardId) {
     auto shardRegistry = Grid::get(opCtx)->shardRegistry();
     auto shardStatus = shardRegistry->getShard(opCtx, shardId);
     if (!shardStatus.isOK()) {
@@ -83,7 +78,7 @@ StatusWith<string> retrieveShardMongoDVersion(OperationContext* opCtx, ShardId s
 
     BSONObj serverStatus = std::move(commandResponse.getValue().response);
 
-    string version;
+    std::string version;
     Status status = bsonExtractStringField(serverStatus, kVersionField, &version);
     if (!status.isOK()) {
         return status;
@@ -100,7 +95,7 @@ ClusterStatisticsImpl::ClusterStatisticsImpl() = default;
 
 ClusterStatisticsImpl::~ClusterStatisticsImpl() = default;
 
-StatusWith<vector<ShardStatistics>> ClusterStatisticsImpl::getStats(OperationContext* opCtx) {
+StatusWith<std::vector<ShardStatistics>> ClusterStatisticsImpl::getStats(OperationContext* opCtx) {
     // Get a list of all the shards that are participating in this balance round along with any
     // maximum allowed quotas and current utilization. We get the latter by issuing
     // db.serverStatus() (mem.mapped) to all shards.
@@ -112,9 +107,9 @@ StatusWith<vector<ShardStatistics>> ClusterStatisticsImpl::getStats(OperationCon
         return shardsStatus.getStatus();
     }
 
-    const vector<ShardType> shards(std::move(shardsStatus.getValue().value));
+    const auto& shards = shardsStatus.getValue().value;
 
-    vector<ShardStatistics> stats;
+    std::vector<ShardStatistics> stats;
 
     for (const auto& shard : shards) {
         const auto shardSizeStatus = [&]() -> StatusWith<long long> {
@@ -133,7 +128,7 @@ StatusWith<vector<ShardStatistics>> ClusterStatisticsImpl::getStats(OperationCon
                                       << shard.getName());
         }
 
-        string mongoDVersion;
+        std::string mongoDVersion;
 
         auto mongoDVersionStatus = retrieveShardMongoDVersion(opCtx, shard.getName());
         if (mongoDVersionStatus.isOK()) {
@@ -145,7 +140,7 @@ StatusWith<vector<ShardStatistics>> ClusterStatisticsImpl::getStats(OperationCon
                   << causedBy(mongoDVersionStatus.getStatus());
         }
 
-        std::set<string> shardTags;
+        std::set<std::string> shardTags;
 
         for (const auto& shardTag : shard.getTags()) {
             shardTags.insert(shardTag);
diff --git a/src/mongo/db/s/balancer/migration_manager.cpp b/src/mongo/db/s/balancer/migration_manager.cpp
index ce7ed13d743..542b2410810 100644
--- a/src/mongo/db/s/balancer/migration_manager.cpp
+++ b/src/mongo/db/s/balancer/migration_manager.cpp
@@ -44,7 +44,6 @@
 #include "mongo/db/s/balancer/type_migration.h"
 #include "mongo/executor/task_executor_pool.h"
 #include "mongo/rpc/get_status_from_command_result.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
@@ -64,6 +63,7 @@ using str::stream;
 namespace {
 
 const char kChunkTooBig[] = "chunkTooBig";  // TODO: delete in 3.8
+
 const WriteConcernOptions kMajorityWriteConcern(WriteConcernOptions::kMajority,
                                                 WriteConcernOptions::SyncMode::UNSET,
                                                 Seconds(15));
diff --git a/src/mongo/db/s/balancer/migration_manager_test.cpp b/src/mongo/db/s/balancer/migration_manager_test.cpp
index 515ebceb7b2..72a32c50627 100644
--- a/src/mongo/db/s/balancer/migration_manager_test.cpp
+++ b/src/mongo/db/s/balancer/migration_manager_test.cpp
@@ -29,13 +29,11 @@
 #include "mongo/platform/basic.h"
 
 #include "mongo/client/remote_command_targeter_mock.h"
-#include "mongo/db/client.h"
 #include "mongo/db/commands.h"
 #include "mongo/db/s/balancer/migration_manager.h"
 #include "mongo/db/s/balancer/type_migration.h"
 #include "mongo/db/write_concern_options.h"
 #include "mongo/s/catalog/dist_lock_manager_mock.h"
-#include "mongo/s/catalog/sharding_catalog_client_impl.h"
 #include "mongo/s/catalog/type_collection.h"
 #include "mongo/s/catalog/type_database.h"
 #include "mongo/s/catalog/type_locks.h"
diff --git a/src/mongo/db/s/balancer/scoped_migration_request.cpp b/src/mongo/db/s/balancer/scoped_migration_request.cpp
index 6cf19c1f4bf..74511ab1823 100644
--- a/src/mongo/db/s/balancer/scoped_migration_request.cpp
+++ b/src/mongo/db/s/balancer/scoped_migration_request.cpp
@@ -32,22 +32,21 @@
 
 #include "mongo/db/s/balancer/scoped_migration_request.h"
 
-#include "mongo/db/repl/replication_coordinator_global.h"
 #include "mongo/db/s/balancer/type_migration.h"
 #include "mongo/db/write_concern_options.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
 #include "mongo/util/log.h"
 
 namespace mongo {
-
 namespace {
+
 const WriteConcernOptions kMajorityWriteConcern(WriteConcernOptions::kMajority,
                                                 WriteConcernOptions::SyncMode::UNSET,
                                                 Seconds(15));
 const int kDuplicateKeyErrorMaxRetries = 2;
-}
+
+}  // namespace
 
 ScopedMigrationRequest::ScopedMigrationRequest(OperationContext* opCtx,
                                                const NamespaceString& nss,
@@ -93,12 +92,13 @@ ScopedMigrationRequest& ScopedMigrationRequest::operator=(ScopedMigrationRequest
 
 StatusWith<ScopedMigrationRequest> ScopedMigrationRequest::writeMigration(
     OperationContext* opCtx, const MigrateInfo& migrateInfo, bool waitForDelete) {
+    auto const grid = Grid::get(opCtx);
 
     // Try to write a unique migration document to config.migrations.
     const MigrationType migrationType(migrateInfo, waitForDelete);
 
     for (int retry = 0; retry < kDuplicateKeyErrorMaxRetries; ++retry) {
-        Status result = grid.catalogClient()->insertConfigDocument(
+        Status result = grid->catalogClient()->insertConfigDocument(
             opCtx, MigrationType::ConfigNS, migrationType.toBSON(), kMajorityWriteConcern);
 
         if (result == ErrorCodes::DuplicateKey) {
@@ -106,7 +106,7 @@ StatusWith<ScopedMigrationRequest> ScopedMigrationRequest::writeMigration(
             // for the request because this migration request will join the active one once
             // scheduled.
             auto statusWithMigrationQueryResult =
-                grid.shardRegistry()->getConfigShard()->exhaustiveFindOnConfig(
+                grid->shardRegistry()->getConfigShard()->exhaustiveFindOnConfig(
                     opCtx,
                     ReadPreferenceSetting{ReadPreference::PrimaryOnly},
                     repl::ReadConcernLevel::kLocalReadConcern,
diff --git a/src/mongo/db/s/chunk_splitter.cpp b/src/mongo/db/s/chunk_splitter.cpp
index f36ed19a0ea..d314b9c5f84 100644
--- a/src/mongo/db/s/chunk_splitter.cpp
+++ b/src/mongo/db/s/chunk_splitter.cpp
@@ -42,7 +42,6 @@
 #include "mongo/db/s/split_chunk.h"
 #include "mongo/db/s/split_vector.h"
 #include "mongo/s/balancer_configuration.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_chunk.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/chunk_manager.h"
diff --git a/src/mongo/db/s/config/configsvr_drop_collection_command.cpp b/src/mongo/db/s/config/configsvr_drop_collection_command.cpp
index f9689722426..bffad346dc6 100644
--- a/src/mongo/db/s/config/configsvr_drop_collection_command.cpp
+++ b/src/mongo/db/s/config/configsvr_drop_collection_command.cpp
@@ -35,7 +35,6 @@
 #include "mongo/db/repl/read_concern_args.h"
 #include "mongo/db/repl/repl_client_info.h"
 #include "mongo/s/catalog/dist_lock_manager.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/sharding_catalog_manager.h"
 #include "mongo/s/catalog/type_database.h"
 #include "mongo/s/catalog_cache.h"
@@ -48,7 +47,6 @@
 #include "mongo/util/scopeguard.h"
 
 namespace mongo {
-
 namespace {
 
 MONGO_FP_DECLARE(setDropCollDistLockWait);
@@ -205,6 +203,7 @@ private:
                 shardId, cmdDropResult.response["writeConcernError"], *result);
         }
     };
+
 } configsvrDropCollectionCmd;
 
 }  // namespace
diff --git a/src/mongo/db/s/config/configsvr_drop_database_command.cpp b/src/mongo/db/s/config/configsvr_drop_database_command.cpp
index 8a9d35df9e8..5a39eee3174 100644
--- a/src/mongo/db/s/config/configsvr_drop_database_command.cpp
+++ b/src/mongo/db/s/config/configsvr_drop_database_command.cpp
@@ -34,11 +34,9 @@
 #include "mongo/db/operation_context.h"
 #include "mongo/db/repl/repl_client_info.h"
 #include "mongo/s/catalog/dist_lock_manager.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/sharding_catalog_manager.h"
 #include "mongo/s/catalog/type_database.h"
 #include "mongo/s/catalog_cache.h"
-#include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
 #include "mongo/util/log.h"
 #include "mongo/util/scopeguard.h"
diff --git a/src/mongo/db/s/config/configsvr_move_primary_command.cpp b/src/mongo/db/s/config/configsvr_move_primary_command.cpp
index 3ff60940242..ad02277cc69 100644
--- a/src/mongo/db/s/config/configsvr_move_primary_command.cpp
+++ b/src/mongo/db/s/config/configsvr_move_primary_command.cpp
@@ -40,7 +40,6 @@
 #include "mongo/db/commands.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/db/repl/repl_client_info.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/sharding_catalog_manager.h"
 #include "mongo/s/catalog/type_database.h"
 #include "mongo/s/catalog_cache.h"
@@ -52,9 +51,6 @@
 #include "mongo/util/scopeguard.h"
 
 namespace mongo {
-
-using std::string;
-
 namespace {
 
 const WriteConcernOptions kMajorityWriteConcern(WriteConcernOptions::kMajority,
@@ -118,7 +114,7 @@ public:
 
         auto movePrimaryRequest =
             MovePrimary::parse(IDLParserErrorContext("ConfigSvrMovePrimary"), cmdObj);
-        const string dbname = parseNs("", cmdObj);
+        const auto dbname = parseNs("", cmdObj);
 
         uassert(
             ErrorCodes::InvalidNamespace,
@@ -249,7 +245,7 @@ public:
         // reload
         catalogCache->purgeDatabase(dbname);
 
-        const string oldPrimary = fromShard->getConnString().toString();
+        const auto oldPrimary = fromShard->getConnString().toString();
 
         ScopedDbConnection fromconn(fromShard->getConnString());
         ON_BLOCK_EXIT([&fromconn] { fromconn.done(); });
diff --git a/src/mongo/db/s/metadata_manager_test.cpp b/src/mongo/db/s/metadata_manager_test.cpp
index 040d4638c70..c66835e5135 100644
--- a/src/mongo/db/s/metadata_manager_test.cpp
+++ b/src/mongo/db/s/metadata_manager_test.cpp
@@ -40,7 +40,6 @@
 #include "mongo/db/repl/replication_coordinator_mock.h"
 #include "mongo/db/s/metadata_manager.h"
 #include "mongo/db/s/sharding_state.h"
-#include "mongo/db/s/type_shard_identity.h"
 #include "mongo/db/server_options.h"
 #include "mongo/db/service_context.h"
 #include "mongo/db/service_context_d_test_fixture.h"
diff --git a/src/mongo/db/s/migration_source_manager.cpp b/src/mongo/db/s/migration_source_manager.cpp
index 6c831b1a0ae..fb1ebee0293 100644
--- a/src/mongo/db/s/migration_source_manager.cpp
+++ b/src/mongo/db/s/migration_source_manager.cpp
@@ -45,11 +45,9 @@
 #include "mongo/db/s/sharding_statistics.h"
 #include "mongo/executor/task_executor.h"
 #include "mongo/executor/task_executor_pool.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_chunk.h"
 #include "mongo/s/catalog/type_shard_collection.h"
 #include "mongo/s/catalog_cache_loader.h"
-#include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
 #include "mongo/s/request_types/commit_chunk_migration_request_type.h"
 #include "mongo/s/request_types/set_shard_version_request.h"
diff --git a/src/mongo/db/s/sharding_task_executor.cpp b/src/mongo/db/s/sharding_task_executor.cpp
deleted file mode 100644
index 5ba9ac969d1..00000000000
--- a/src/mongo/db/s/sharding_task_executor.cpp
+++ /dev/null
@@ -1,207 +0,0 @@
-/**
- *    Copyright (C) 2017 MongoDB Inc.
- *
- *    This program is free software: you can redistribute it and/or  modify
- *    it under the terms of the GNU Affero General Public License, version 3,
- *    as published by the Free Software Foundation.
- *
- *    This program is distributed in the hope that it will be useful,
- *    but WITHOUT ANY WARRANTY; without even the implied warranty of
- *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *    GNU Affero General Public License for more details.
- *
- *    You should have received a copy of the GNU Affero General Public License
- *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
- *    As a special exception, the copyright holders give permission to link the
- *    code of portions of this program with the OpenSSL library under certain
- *    conditions as described in each individual source file and distribute
- *    linked combinations including the program with the OpenSSL library. You
- *    must comply with the GNU Affero General Public License in all respects for
- *    all of the code used other than as permitted herein. If you modify file(s)
- *    with this exception, you may extend this exception to your version of the
- *    file(s), but you are not obligated to do so. If you do not wish to do so,
- *    delete this exception statement from your version. If you delete this
- *    exception statement from all source files in the program, then also delete
- *    it in the license file.
- */
-
-#define MONGO_LOG_DEFAULT_COMPONENT mongo::logger::LogComponent::kSharding
-
-#include "mongo/platform/basic.h"
-
-#include "mongo/db/s/sharding_task_executor.h"
-
-#include "mongo/base/disallow_copying.h"
-#include "mongo/base/status_with.h"
-#include "mongo/bson/timestamp.h"
-#include "mongo/db/logical_time.h"
-#include "mongo/db/operation_time_tracker.h"
-#include "mongo/executor/thread_pool_task_executor.h"
-#include "mongo/rpc/get_status_from_command_result.h"
-#include "mongo/rpc/metadata/sharding_metadata.h"
-#include "mongo/s/client/shard_registry.h"
-#include "mongo/s/cluster_last_error_info.h"
-#include "mongo/s/grid.h"
-#include "mongo/util/log.h"
-#include "mongo/util/scopeguard.h"
-
-namespace mongo {
-namespace executor {
-
-namespace {
-const std::string kOperationTimeField = "operationTime";
-}
-
-ShardingTaskExecutor::ShardingTaskExecutor(std::unique_ptr<ThreadPoolTaskExecutor> executor)
-    : _executor(std::move(executor)) {}
-
-void ShardingTaskExecutor::startup() {
-    _executor->startup();
-}
-
-void ShardingTaskExecutor::shutdown() {
-    _executor->shutdown();
-}
-
-void ShardingTaskExecutor::join() {
-    _executor->join();
-}
-
-void ShardingTaskExecutor::appendDiagnosticBSON(mongo::BSONObjBuilder* builder) const {
-    _executor->appendDiagnosticBSON(builder);
-}
-
-Date_t ShardingTaskExecutor::now() {
-    return _executor->now();
-}
-
-StatusWith<TaskExecutor::EventHandle> ShardingTaskExecutor::makeEvent() {
-    return _executor->makeEvent();
-}
-
-void ShardingTaskExecutor::signalEvent(const EventHandle& event) {
-    return _executor->signalEvent(event);
-}
-
-StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::onEvent(const EventHandle& event,
-                                                                       const CallbackFn& work) {
-    return _executor->onEvent(event, work);
-}
-
-void ShardingTaskExecutor::waitForEvent(const EventHandle& event) {
-    _executor->waitForEvent(event);
-}
-
-StatusWith<stdx::cv_status> ShardingTaskExecutor::waitForEvent(OperationContext* opCtx,
-                                                               const EventHandle& event,
-                                                               Date_t deadline) {
-    return _executor->waitForEvent(opCtx, event, deadline);
-}
-
-StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::scheduleWork(
-    const CallbackFn& work) {
-    return _executor->scheduleWork(work);
-}
-
-StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::scheduleWorkAt(
-    Date_t when, const CallbackFn& work) {
-    return _executor->scheduleWorkAt(when, work);
-}
-
-StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::scheduleRemoteCommand(
-    const RemoteCommandRequest& request, const RemoteCommandCallbackFn& cb) {
-
-    // schedule the user's callback if there is not opCtx
-    if (!request.opCtx) {
-        return _executor->scheduleRemoteCommand(request, cb);
-    }
-
-    boost::optional<RemoteCommandRequest> newRequest;
-
-    if (request.opCtx->getLogicalSessionId() && !request.cmdObj.hasField("lsid")) {
-        newRequest.emplace(request);
-        BSONObjBuilder bob(std::move(newRequest->cmdObj));
-        {
-            BSONObjBuilder subbob(bob.subobjStart("lsid"));
-            request.opCtx->getLogicalSessionId()->serialize(&subbob);
-        }
-
-        newRequest->cmdObj = bob.obj();
-    }
-
-    std::shared_ptr<OperationTimeTracker> timeTracker = OperationTimeTracker::get(request.opCtx);
-
-    auto clusterGLE = ClusterLastErrorInfo::get(request.opCtx->getClient());
-
-    auto shardingCb = [timeTracker, clusterGLE, cb](
-        const TaskExecutor::RemoteCommandCallbackArgs& args) {
-        ON_BLOCK_EXIT([&cb, &args]() { cb(args); });
-
-        // Update replica set monitor info.
-        auto shard = grid.shardRegistry()->getShardForHostNoReload(args.request.target);
-        if (!shard) {
-            LOG(1) << "Could not find shard containing host: " << args.request.target.toString();
-        }
-
-        if (!args.response.isOK()) {
-            if (shard) {
-                shard->updateReplSetMonitor(args.request.target, args.response.status);
-            }
-            LOG(1) << "Error processing the remote request, not updating operationTime or gLE";
-            return;
-        }
-
-        if (shard) {
-            shard->updateReplSetMonitor(args.request.target,
-                                        getStatusFromCommandResult(args.response.data));
-        }
-
-        // Update the logical clock.
-        invariant(timeTracker);
-        auto operationTime = args.response.data[kOperationTimeField];
-        if (!operationTime.eoo()) {
-            invariant(operationTime.type() == BSONType::bsonTimestamp);
-            timeTracker->updateOperationTime(LogicalTime(operationTime.timestamp()));
-        }
-
-        // Update getLastError info for the client if we're tracking it.
-        if (clusterGLE) {
-            auto swShardingMetadata =
-                rpc::ShardingMetadata::readFromMetadata(args.response.metadata);
-            if (swShardingMetadata.isOK()) {
-                auto shardingMetadata = std::move(swShardingMetadata.getValue());
-
-                auto shardConn = ConnectionString::parse(args.request.target.toString());
-                if (!shardConn.isOK()) {
-                    severe() << "got bad host string in saveGLEStats: " << args.request.target;
-                }
-
-                clusterGLE->addHostOpTime(shardConn.getValue(),
-                                          HostOpTime(shardingMetadata.getLastOpTime(),
-                                                     shardingMetadata.getLastElectionId()));
-            } else if (swShardingMetadata.getStatus() != ErrorCodes::NoSuchKey) {
-                warning() << "Got invalid sharding metadata "
-                          << redact(swShardingMetadata.getStatus()) << " metadata object was '"
-                          << redact(args.response.metadata) << "'";
-            }
-        }
-    };
-
-    return _executor->scheduleRemoteCommand(newRequest ? *newRequest : request, shardingCb);
-}
-
-void ShardingTaskExecutor::cancel(const CallbackHandle& cbHandle) {
-    _executor->cancel(cbHandle);
-}
-
-void ShardingTaskExecutor::wait(const CallbackHandle& cbHandle) {
-    _executor->wait(cbHandle);
-}
-
-void ShardingTaskExecutor::appendConnectionStats(ConnectionPoolStats* stats) const {
-    _executor->appendConnectionStats(stats);
-}
-
-}  // namespace executor
-}  // namespace mongo
diff --git a/src/mongo/db/s/sharding_task_executor.h b/src/mongo/db/s/sharding_task_executor.h
deleted file mode 100644
index 4c2571c684a..00000000000
--- a/src/mongo/db/s/sharding_task_executor.h
+++ /dev/null
@@ -1,82 +0,0 @@
-/**
- *    Copyright (C) 2017 MongoDB Inc.
- *
- *    This program is free software: you can redistribute it and/or  modify
- *    it under the terms of the GNU Affero General Public License, version 3,
- *    as published by the Free Software Foundation.
- *
- *    This program is distributed in the hope that it will be useful,
- *    but WITHOUT ANY WARRANTY; without even the implied warranty of
- *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *    GNU Affero General Public License for more details.
- *
- *    You should have received a copy of the GNU Affero General Public License
- *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
- *    As a special exception, the copyright holders give permission to link the
- *    code of portions of this program with the OpenSSL library under certain
- *    conditions as described in each individual source file and distribute
- *    linked combinations including the program with the OpenSSL library. You
- *    must comply with the GNU Affero General Public License in all respects for
- *    all of the code used other than as permitted herein. If you modify file(s)
- *    with this exception, you may extend this exception to your version of the
- *    file(s), but you are not obligated to do so. If you do not wish to do so,
- *    delete this exception statement from your version. If you delete this
- *    exception statement from all source files in the program, then also delete
- *    it in the license file.
- */
-
-#pragma once
-
-#include <memory>
-
-#include "mongo/base/disallow_copying.h"
-#include "mongo/base/status_with.h"
-#include "mongo/executor/task_executor.h"
-#include "mongo/stdx/condition_variable.h"
-#include "mongo/stdx/list.h"
-#include "mongo/stdx/mutex.h"
-
-namespace mongo {
-namespace executor {
-
-struct ConnectionPoolStats;
-class ThreadPoolTaskExecutor;
-
-/**
- * Implementation of a TaskExecutor that uses ThreadPoolTaskExecutor to submit tasks and allows to
- * override methods if needed.
- */
-class ShardingTaskExecutor final : public TaskExecutor {
-    MONGO_DISALLOW_COPYING(ShardingTaskExecutor);
-
-public:
-    ShardingTaskExecutor(std::unique_ptr<ThreadPoolTaskExecutor> executor);
-
-    void startup() override;
-    void shutdown() override;
-    void join() override;
-    void appendDiagnosticBSON(BSONObjBuilder* builder) const override;
-    Date_t now() override;
-    StatusWith<EventHandle> makeEvent() override;
-    void signalEvent(const EventHandle& event) override;
-    StatusWith<CallbackHandle> onEvent(const EventHandle& event, const CallbackFn& work) override;
-    void waitForEvent(const EventHandle& event) override;
-    StatusWith<stdx::cv_status> waitForEvent(OperationContext* opCtx,
-                                             const EventHandle& event,
-                                             Date_t deadline) override;
-    StatusWith<CallbackHandle> scheduleWork(const CallbackFn& work) override;
-    StatusWith<CallbackHandle> scheduleWorkAt(Date_t when, const CallbackFn& work) override;
-    StatusWith<CallbackHandle> scheduleRemoteCommand(const RemoteCommandRequest& request,
-                                                     const RemoteCommandCallbackFn& cb) override;
-    void cancel(const CallbackHandle& cbHandle) override;
-    void wait(const CallbackHandle& cbHandle) override;
-
-    void appendConnectionStats(ConnectionPoolStats* stats) const override;
-
-private:
-    std::unique_ptr<ThreadPoolTaskExecutor> _executor;
-};
-
-}  // namespace executor
-}  // namespace mongo
diff --git a/src/mongo/db/server_options.cpp b/src/mongo/db/server_options.cpp
index d37442e4519..bc01417b6f8 100644
--- a/src/mongo/db/server_options.cpp
+++ b/src/mongo/db/server_options.cpp
@@ -25,6 +25,8 @@
  *    then also delete it in the license file.
  */
 
+#include "mongo/platform/basic.h"
+
 #include "mongo/db/server_options.h"
 
 namespace mongo {
diff --git a/src/mongo/db/server_options.h b/src/mongo/db/server_options.h
index 826f5760313..478fdbab935 100644
--- a/src/mongo/db/server_options.h
+++ b/src/mongo/db/server_options.h
@@ -30,7 +30,6 @@
 #include "mongo/db/jsobj.h"
 #include "mongo/platform/atomic_word.h"
 #include "mongo/platform/process_id.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 
 namespace mongo {
 
diff --git a/src/mongo/db/service_context_d.cpp b/src/mongo/db/service_context_d.cpp
index 15e39126539..980bea314b0 100644
--- a/src/mongo/db/service_context_d.cpp
+++ b/src/mongo/db/service_context_d.cpp
@@ -36,6 +36,7 @@
 #include "mongo/base/initializer.h"
 #include "mongo/db/client.h"
 #include "mongo/db/concurrency/lock_state.h"
+#include "mongo/db/operation_context.h"
 #include "mongo/db/service_entry_point_mongod.h"
 #include "mongo/db/storage/storage_engine.h"
 #include "mongo/db/storage/storage_engine_lock_file.h"
diff --git a/src/mongo/rpc/command_request.cpp b/src/mongo/rpc/command_request.cpp
index 44accc8b8f0..98e85f02f5f 100644
--- a/src/mongo/rpc/command_request.cpp
+++ b/src/mongo/rpc/command_request.cpp
@@ -38,6 +38,7 @@
 #include "mongo/base/data_type_terminated.h"
 #include "mongo/base/data_type_validated.h"
 #include "mongo/bson/simple_bsonobj_comparator.h"
+#include "mongo/client/read_preference.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/rpc/object_check.h"
 #include "mongo/util/assert_util.h"
diff --git a/src/mongo/s/SConscript b/src/mongo/s/SConscript
index de20bdb4489..16687b6567d 100644
--- a/src/mongo/s/SConscript
+++ b/src/mongo/s/SConscript
@@ -24,17 +24,17 @@ env.Library(
         'sharding_initialization.cpp',
     ],
     LIBDEPS=[
+        '$BUILD_DIR/mongo/db/logical_session_cache_factory_mongos',
         '$BUILD_DIR/mongo/executor/network_interface_factory',
         '$BUILD_DIR/mongo/executor/network_interface_thread_pool',
         '$BUILD_DIR/mongo/executor/thread_pool_task_executor',
-        '$BUILD_DIR/mongo/s/catalog/sharding_catalog_client_impl',
         '$BUILD_DIR/mongo/s/catalog/dist_lock_catalog_impl',
         '$BUILD_DIR/mongo/s/catalog/replset_dist_lock_manager',
-        '$BUILD_DIR/mongo/db/logical_session_cache_factory_mongos',
-        '$BUILD_DIR/mongo/db/s/sharding_task_executor',
+        '$BUILD_DIR/mongo/s/catalog/sharding_catalog_client_impl',
         '$BUILD_DIR/mongo/util/periodic_runner_factory',
         'client/sharding_connection_hook',
         'coreshard',
+        'sharding_task_executor',
     ],
 )
 
@@ -106,7 +106,6 @@ env.Library(
         '$BUILD_DIR/mongo/client/remote_command_targeter_mock',
         '$BUILD_DIR/mongo/db/auth/authorization_manager_mock_init',
         '$BUILD_DIR/mongo/db/query/collation/collator_factory_mock',
-        '$BUILD_DIR/mongo/db/s/sharding_task_executor',
         '$BUILD_DIR/mongo/db/service_context_noop_init',
         '$BUILD_DIR/mongo/executor/network_test_env',
         '$BUILD_DIR/mongo/executor/task_executor_pool',
@@ -117,6 +116,7 @@ env.Library(
         '$BUILD_DIR/mongo/transport/transport_layer_mock',
         '$BUILD_DIR/mongo/util/clock_source_mock',
         'sharding_egress_metadata_hook_for_mongos',
+        'sharding_task_executor',
     ],
 )
 
@@ -235,6 +235,20 @@ env.Library(
     ],
 )
 
+
+env.Library(
+    target='sharding_task_executor',
+    source=[
+        'sharding_task_executor.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+        '$BUILD_DIR/mongo/executor/thread_pool_task_executor',
+        '$BUILD_DIR/mongo/s/client/sharding_client',
+        '$BUILD_DIR/mongo/s/cluster_last_error_info',
+    ],
+)
+
 env.Library(
     target='stale_config',
     source=[
diff --git a/src/mongo/s/catalog/sharding_catalog_client_impl.cpp b/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
index 7da59f057c3..bf99877d6df 100644
--- a/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
+++ b/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
@@ -50,7 +50,6 @@
 #include "mongo/db/repl/optime.h"
 #include "mongo/db/repl/read_concern_args.h"
 #include "mongo/db/repl/repl_client_info.h"
-#include "mongo/db/s/type_shard_identity.h"
 #include "mongo/executor/network_interface.h"
 #include "mongo/executor/task_executor.h"
 #include "mongo/rpc/get_status_from_command_result.h"
diff --git a/src/mongo/s/catalog/sharding_catalog_client_mock.h b/src/mongo/s/catalog/sharding_catalog_client_mock.h
index 7ab8c63ddef..5b81aadbdac 100644
--- a/src/mongo/s/catalog/sharding_catalog_client_mock.h
+++ b/src/mongo/s/catalog/sharding_catalog_client_mock.h
@@ -28,7 +28,6 @@
 
 #pragma once
 
-#include "mongo/s/catalog/dist_lock_manager.h"
 #include "mongo/s/catalog/sharding_catalog_client.h"
 
 namespace mongo {
diff --git a/src/mongo/s/catalog_cache.cpp b/src/mongo/s/catalog_cache.cpp
index bf072e10df4..a1f44b678f2 100644
--- a/src/mongo/s/catalog_cache.cpp
+++ b/src/mongo/s/catalog_cache.cpp
@@ -37,8 +37,6 @@
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/db/query/collation/collator_factory_interface.h"
 #include "mongo/db/repl/optime_with.h"
-#include "mongo/platform/unordered_set.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_collection.h"
 #include "mongo/s/catalog/type_database.h"
 #include "mongo/s/client/shard_registry.h"
diff --git a/src/mongo/s/client/version_manager.cpp b/src/mongo/s/client/version_manager.cpp
index 27016c0a566..bbd3d5f8555 100644
--- a/src/mongo/s/client/version_manager.cpp
+++ b/src/mongo/s/client/version_manager.cpp
@@ -34,10 +34,7 @@
 
 #include "mongo/client/dbclient_rs.h"
 #include "mongo/db/namespace_string.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog_cache.h"
-#include "mongo/s/catalog_cache.h"
-#include "mongo/s/chunk_version.h"
 #include "mongo/s/client/shard_connection.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
diff --git a/src/mongo/s/commands/cluster_add_shard_cmd.cpp b/src/mongo/s/commands/cluster_add_shard_cmd.cpp
index df13a652f37..39225a4b854 100644
--- a/src/mongo/s/commands/cluster_add_shard_cmd.cpp
+++ b/src/mongo/s/commands/cluster_add_shard_cmd.cpp
@@ -30,13 +30,7 @@
 
 #include "mongo/platform/basic.h"
 
-#include <vector>
-
-#include "mongo/bson/util/bson_extract.h"
-#include "mongo/db/audit.h"
 #include "mongo/db/commands.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
-#include "mongo/s/catalog/type_shard.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
 #include "mongo/s/request_types/add_shard_request_type.h"
@@ -44,9 +38,6 @@
 #include "mongo/util/scopeguard.h"
 
 namespace mongo {
-
-using std::string;
-
 namespace {
 
 const ReadPreferenceSetting kPrimaryOnlyReadPreference{ReadPreference::PrimaryOnly};
@@ -60,11 +51,11 @@ public:
         return AllowedOnSecondary::kAlways;
     }
 
-    virtual bool adminOnly() const {
+    bool adminOnly() const override {
         return true;
     }
 
-    virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
+    bool supportsWriteConcern(const BSONObj& cmd) const override {
         return true;
     }
 
@@ -72,18 +63,18 @@ public:
         return "add a new shard to the system";
     }
 
-    virtual void addRequiredPrivileges(const std::string& dbname,
-                                       const BSONObj& cmdObj,
-                                       std::vector<Privilege>* out) {
+    void addRequiredPrivileges(const std::string& dbname,
+                               const BSONObj& cmdObj,
+                               std::vector<Privilege>* out) override {
         ActionSet actions;
         actions.addAction(ActionType::addShard);
         out->push_back(Privilege(ResourcePattern::forClusterResource(), actions));
     }
 
-    virtual bool run(OperationContext* opCtx,
-                     const std::string& dbname,
-                     const BSONObj& cmdObj,
-                     BSONObjBuilder& result) {
+    bool run(OperationContext* opCtx,
+             const std::string& dbname,
+             const BSONObj& cmdObj,
+             BSONObjBuilder& result) override {
         auto parsedRequest = uassertStatusOK(AddShardRequest::parseFromMongosCommand(cmdObj));
 
         // Force a reload of this node's shard list cache at the end of this command.
@@ -106,7 +97,7 @@ public:
         return true;
     }
 
-} addShard;
+} addShardCmd;
 
 }  // namespace
 }  // namespace mongo
diff --git a/src/mongo/s/commands/cluster_add_shard_to_zone_cmd.cpp b/src/mongo/s/commands/cluster_add_shard_to_zone_cmd.cpp
index ca9f56b0ab7..8289bef85b0 100644
--- a/src/mongo/s/commands/cluster_add_shard_to_zone_cmd.cpp
+++ b/src/mongo/s/commands/cluster_add_shard_to_zone_cmd.cpp
@@ -30,13 +30,9 @@
 
 #include "mongo/platform/basic.h"
 
-#include <vector>
-
-#include "mongo/bson/util/bson_extract.h"
 #include "mongo/db/auth/authorization_session.h"
 #include "mongo/db/commands.h"
 #include "mongo/db/write_concern_options.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_shard.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
@@ -44,9 +40,6 @@
 #include "mongo/util/log.h"
 
 namespace mongo {
-
-using std::string;
-
 namespace {
 
 const ReadPreferenceSetting kPrimaryOnlyReadPreference{ReadPreference::PrimaryOnly};
@@ -73,11 +66,11 @@ public:
         return AllowedOnSecondary::kAlways;
     }
 
-    virtual bool adminOnly() const {
+    bool adminOnly() const override {
         return true;
     }
 
-    virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
+    bool supportsWriteConcern(const BSONObj& cmd) const override {
         return false;
     }
 
@@ -95,10 +88,10 @@ public:
         return Status::OK();
     }
 
-    virtual bool run(OperationContext* opCtx,
-                     const std::string& dbname,
-                     const BSONObj& cmdObj,
-                     BSONObjBuilder& result) {
+    bool run(OperationContext* opCtx,
+             const std::string& dbname,
+             const BSONObj& cmdObj,
+             BSONObjBuilder& result) override {
         auto parsedRequest = uassertStatusOK(AddShardToZoneRequest::parseFromMongosCommand(cmdObj));
 
         BSONObjBuilder cmdBuilder;
diff --git a/src/mongo/s/commands/cluster_enable_sharding_cmd.cpp b/src/mongo/s/commands/cluster_enable_sharding_cmd.cpp
index 1869632ef68..ba7bd608612 100644
--- a/src/mongo/s/commands/cluster_enable_sharding_cmd.cpp
+++ b/src/mongo/s/commands/cluster_enable_sharding_cmd.cpp
@@ -30,17 +30,13 @@
 
 #include "mongo/platform/basic.h"
 
-#include "mongo/db/audit.h"
 #include "mongo/db/auth/action_set.h"
 #include "mongo/db/auth/action_type.h"
 #include "mongo/db/auth/authorization_manager.h"
 #include "mongo/db/auth/authorization_session.h"
-#include "mongo/db/client.h"
 #include "mongo/db/commands.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/client/shard_registry.h"
-#include "mongo/s/commands/cluster_commands_helpers.h"
 #include "mongo/s/grid.h"
 #include "mongo/util/log.h"
 #include "mongo/util/scopeguard.h"
@@ -56,11 +52,11 @@ public:
         return AllowedOnSecondary::kAlways;
     }
 
-    virtual bool adminOnly() const {
+    bool adminOnly() const override {
         return true;
     }
 
-    virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
+    bool supportsWriteConcern(const BSONObj& cmd) const override {
         return true;
     }
 
@@ -70,9 +66,9 @@ public:
                "  { enablesharding : \"<dbname>\" }\n";
     }
 
-    virtual Status checkAuthForCommand(Client* client,
-                                       const std::string& dbname,
-                                       const BSONObj& cmdObj) {
+    Status checkAuthForCommand(Client* client,
+                               const std::string& dbname,
+                               const BSONObj& cmdObj) override {
         if (!AuthorizationSession::get(client)->isAuthorizedForActionsOnResource(
                 ResourcePattern::forDatabaseName(parseNs(dbname, cmdObj)),
                 ActionType::enableSharding)) {
@@ -82,15 +78,15 @@ public:
         return Status::OK();
     }
 
-    virtual std::string parseNs(const std::string& dbname, const BSONObj& cmdObj) const {
+    std::string parseNs(const std::string& dbname_unused, const BSONObj& cmdObj) const override {
         return cmdObj.firstElement().str();
     }
 
-    virtual bool errmsgRun(OperationContext* opCtx,
-                           const std::string& dbname_unused,
-                           const BSONObj& cmdObj,
-                           std::string& errmsg,
-                           BSONObjBuilder& result) {
+    bool errmsgRun(OperationContext* opCtx,
+                   const std::string& dbname_unused,
+                   const BSONObj& cmdObj,
+                   std::string& errmsg,
+                   BSONObjBuilder& result) override {
         const std::string db = parseNs("", cmdObj);
 
         // Invalidate the routing table cache entry for this database so that we reload the
@@ -110,7 +106,7 @@ public:
         return true;
     }
 
-} clusterEnableShardingCmd;
+} enableShardingCmd;
 
 }  // namespace
 }  // namespace mongo
diff --git a/src/mongo/s/commands/cluster_list_databases_cmd.cpp b/src/mongo/s/commands/cluster_list_databases_cmd.cpp
index 064b89d3ca4..10d9c802a46 100644
--- a/src/mongo/s/commands/cluster_list_databases_cmd.cpp
+++ b/src/mongo/s/commands/cluster_list_databases_cmd.cpp
@@ -29,7 +29,6 @@
 #include "mongo/platform/basic.h"
 
 #include <map>
-#include <string>
 #include <vector>
 
 #include "mongo/bson/util/bson_extract.h"
@@ -37,35 +36,28 @@
 #include "mongo/client/remote_command_targeter.h"
 #include "mongo/db/auth/authorization_session.h"
 #include "mongo/db/commands.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/client/shard.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/commands/strategy.h"
 #include "mongo/s/grid.h"
 
 namespace mongo {
-
-using std::unique_ptr;
-using std::map;
-using std::string;
-using std::vector;
-
 namespace {
 
 class ListDatabasesCmd : public BasicCommand {
 public:
     ListDatabasesCmd() : BasicCommand("listDatabases", "listdatabases") {}
 
-    AllowedOnSecondary secondaryAllowed() const final {
+    AllowedOnSecondary secondaryAllowed() const override {
         return AllowedOnSecondary::kAlways;
     }
 
-    bool adminOnly() const final {
+    bool adminOnly() const override {
         return true;
     }
 
 
-    bool supportsWriteConcern(const BSONObj& cmd) const final {
+    bool supportsWriteConcern(const BSONObj& cmd) const override {
         return false;
     }
 
@@ -80,7 +72,7 @@ public:
      */
     Status checkAuthForCommand(Client* client,
                                const std::string& dbname,
-                               const BSONObj& cmdObj) final {
+                               const BSONObj& cmdObj) override {
         return Status::OK();
     }
 
@@ -88,13 +80,13 @@ public:
     bool run(OperationContext* opCtx,
              const std::string& dbname_unused,
              const BSONObj& cmdObj,
-             BSONObjBuilder& result) final {
+             BSONObjBuilder& result) override {
         const bool nameOnly = cmdObj["nameOnly"].trueValue();
 
-        map<string, long long> sizes;
-        map<string, unique_ptr<BSONObjBuilder>> dbShardInfo;
+        std::map<std::string, long long> sizes;
+        std::map<std::string, std::unique_ptr<BSONObjBuilder>> dbShardInfo;
 
-        vector<ShardId> shardIds;
+        std::vector<ShardId> shardIds;
         grid.shardRegistry()->getAllShardIds(&shardIds);
         shardIds.emplace_back(ShardRegistry::kConfigServerShardId);
 
@@ -120,7 +112,7 @@ public:
             while (j.more()) {
                 BSONObj dbObj = j.next().Obj();
 
-                const string name = dbObj["name"].String();
+                const auto name = dbObj["name"].String();
 
                 // If this is the admin db, only collect its stats from the config servers.
                 if (name == "admin" && !s->isConfig()) {
@@ -143,8 +135,8 @@ public:
                     sizeSumForDbAcrossShards += size;
                 }
 
-                unique_ptr<BSONObjBuilder>& bb = dbShardInfo[name];
-                if (!bb.get()) {
+                auto& bb = dbShardInfo[name];
+                if (!bb) {
                     bb.reset(new BSONObjBuilder());
                 }
 
@@ -163,15 +155,16 @@ public:
         // Now that we have aggregated results for all the shards, convert to a response,
         // and compute total sizes.
         long long totalSize = 0;
+
         {
             BSONArrayBuilder dbListBuilder(result.subarrayStart("databases"));
-            for (map<string, long long>::iterator i = sizes.begin(); i != sizes.end(); ++i) {
-                const string name = i->first;
+            for (const auto& sizeEntry : sizes) {
+                const auto& name = sizeEntry.first;
+                const long long size = sizeEntry.second;
 
-                if (name == "local") {
-                    // We don't return local, since all shards have their own independent local
+                // Skip the local database, since all shards have their own independent local
+                if (name == NamespaceString::kLocalDb)
                     continue;
-                }
 
                 if (checkAuth && as &&
                     !as->isAuthorizedForActionsOnResource(ResourcePattern::forDatabaseName(name),
@@ -180,8 +173,6 @@ public:
                     continue;
                 }
 
-                long long size = i->second;
-
                 BSONObjBuilder temp;
                 temp.append("name", name);
                 if (!nameOnly) {
@@ -208,7 +199,7 @@ public:
         return true;
     }
 
-} clusterCmdListDatabases;
+} listDatabasesCmd;
 
 }  // namespace
 }  // namespace mongo
diff --git a/src/mongo/s/commands/cluster_list_shards_cmd.cpp b/src/mongo/s/commands/cluster_list_shards_cmd.cpp
index 59ceb90f106..e3d65fabe99 100644
--- a/src/mongo/s/commands/cluster_list_shards_cmd.cpp
+++ b/src/mongo/s/commands/cluster_list_shards_cmd.cpp
@@ -28,10 +28,7 @@
 
 #include "mongo/platform/basic.h"
 
-#include <vector>
-
 #include "mongo/db/commands.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_shard.h"
 #include "mongo/s/grid.h"
 
@@ -83,7 +80,7 @@ public:
         return true;
     }
 
-} listShards;
+} listShardsCmd;
 
 }  // namespace
 }  // namespace mongo
diff --git a/src/mongo/s/commands/cluster_user_management_commands.cpp b/src/mongo/s/commands/cluster_user_management_commands.cpp
index 1bbe5984ca8..aa048b3b575 100644
--- a/src/mongo/s/commands/cluster_user_management_commands.cpp
+++ b/src/mongo/s/commands/cluster_user_management_commands.cpp
@@ -30,8 +30,6 @@
 
 #include "mongo/platform/basic.h"
 
-#include "mongo/db/commands/user_management_commands.h"
-
 #include "mongo/base/status.h"
 #include "mongo/bson/mutable/document.h"
 #include "mongo/client/dbclientinterface.h"
@@ -40,9 +38,9 @@
 #include "mongo/db/auth/authorization_manager_global.h"
 #include "mongo/db/auth/user_management_commands_parser.h"
 #include "mongo/db/commands.h"
+#include "mongo/db/commands/user_management_commands.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/rpc/write_concern_error_detail.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_shard.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/commands/cluster_commands_helpers.h"
diff --git a/src/mongo/s/commands/cluster_write.cpp b/src/mongo/s/commands/cluster_write.cpp
index 012ec0b17d8..517f71606d3 100644
--- a/src/mongo/s/commands/cluster_write.cpp
+++ b/src/mongo/s/commands/cluster_write.cpp
@@ -39,7 +39,6 @@
 #include "mongo/db/lasterror.h"
 #include "mongo/db/write_concern_options.h"
 #include "mongo/s/balancer_configuration.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_collection.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/client/shard_registry.h"
diff --git a/src/mongo/s/commands/commands_public.cpp b/src/mongo/s/commands/commands_public.cpp
index 1ce1611ff25..32ce21b65ea 100644
--- a/src/mongo/s/commands/commands_public.cpp
+++ b/src/mongo/s/commands/commands_public.cpp
@@ -53,7 +53,6 @@
 #include "mongo/executor/task_executor_pool.h"
 #include "mongo/rpc/get_status_from_command_result.h"
 #include "mongo/s/async_requests_sender.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/client/shard_connection.h"
 #include "mongo/s/client/shard_registry.h"
diff --git a/src/mongo/s/grid.cpp b/src/mongo/s/grid.cpp
index b96f4986197..e27d34f3891 100644
--- a/src/mongo/s/grid.cpp
+++ b/src/mongo/s/grid.cpp
@@ -37,12 +37,9 @@
 #include "mongo/executor/task_executor.h"
 #include "mongo/executor/task_executor_pool.h"
 #include "mongo/s/balancer_configuration.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/client/shard_factory.h"
-#include "mongo/s/client/shard_registry.h"
 #include "mongo/s/query/cluster_cursor_manager.h"
-#include "mongo/stdx/memory.h"
 #include "mongo/util/log.h"
 
 namespace mongo {
diff --git a/src/mongo/s/grid.h b/src/mongo/s/grid.h
index 1a14ad361e5..ba47fa07c4e 100644
--- a/src/mongo/s/grid.h
+++ b/src/mongo/s/grid.h
@@ -29,6 +29,8 @@
 #pragma once
 
 #include "mongo/db/repl/optime.h"
+#include "mongo/s/catalog/sharding_catalog_client.h"
+#include "mongo/s/client/shard_registry.h"
 #include "mongo/stdx/functional.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/stdx/mutex.h"
@@ -37,11 +39,9 @@ namespace mongo {
 
 class BalancerConfiguration;
 class CatalogCache;
-class ShardingCatalogClient;
 class ClusterCursorManager;
 class OperationContext;
 class ServiceContext;
-class ShardRegistry;
 
 namespace executor {
 struct ConnectionPoolStats;
diff --git a/src/mongo/s/server.cpp b/src/mongo/s/server.cpp
index c0d99811094..2a38a9a136e 100644
--- a/src/mongo/s/server.cpp
+++ b/src/mongo/s/server.cpp
@@ -70,7 +70,6 @@
 #include "mongo/platform/process_id.h"
 #include "mongo/rpc/metadata/egress_metadata_hook_list.h"
 #include "mongo/s/balancer_configuration.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog_cache.h"
 #include "mongo/s/client/shard_connection.h"
 #include "mongo/s/client/shard_factory.h"
@@ -133,10 +132,13 @@ boost::optional<ShardingUptimeReporter> shardingUptimeReporter;
 static constexpr auto kRetryInterval = Seconds{1};
 
 Status waitForSigningKeys(OperationContext* opCtx) {
+    auto const shardRegistry = Grid::get(opCtx)->shardRegistry();
+
     while (true) {
-        // this should be true when shard registry is up
-        invariant(grid.shardRegistry()->isUp());
-        auto configCS = grid.shardRegistry()->getConfigServerConnectionString();
+        // This should be true when shard registry is up
+        invariant(shardRegistry->isUp());
+
+        auto configCS = shardRegistry->getConfigServerConnectionString();
         auto rsm = ReplicaSetMonitor::get(configCS.getSetName());
         // mongod will set minWireVersion == maxWireVersion for isMaster requests from
         // internalClient.
diff --git a/src/mongo/s/sharding_initialization.cpp b/src/mongo/s/sharding_initialization.cpp
index 3dd9b60f8ce..1bb4215fa2c 100644
--- a/src/mongo/s/sharding_initialization.cpp
+++ b/src/mongo/s/sharding_initialization.cpp
@@ -42,7 +42,6 @@
 #include "mongo/db/logical_clock.h"
 #include "mongo/db/logical_time_validator.h"
 #include "mongo/db/repl/replication_coordinator.h"
-#include "mongo/db/s/sharding_task_executor.h"
 #include "mongo/db/server_options.h"
 #include "mongo/db/server_parameters.h"
 #include "mongo/db/service_context.h"
@@ -66,6 +65,7 @@
 #include "mongo/s/cluster_identity_loader.h"
 #include "mongo/s/grid.h"
 #include "mongo/s/query/cluster_cursor_manager.h"
+#include "mongo/s/sharding_task_executor.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/exit.h"
 #include "mongo/util/log.h"
@@ -278,7 +278,7 @@ Status waitForShardRegistryReload(OperationContext* opCtx) {
         try {
             uassertStatusOK(ClusterIdentityLoader::get(opCtx)->loadClusterId(
                 opCtx, repl::ReadConcernLevel::kMajorityReadConcern));
-            if (grid.shardRegistry()->isUp()) {
+            if (Grid::get(opCtx)->shardRegistry()->isUp()) {
                 return Status::OK();
             }
             sleepFor(kRetryInterval);
diff --git a/src/mongo/s/sharding_mongod_test_fixture.h b/src/mongo/s/sharding_mongod_test_fixture.h
index 6ac9a636326..aca1a3f22c0 100644
--- a/src/mongo/s/sharding_mongod_test_fixture.h
+++ b/src/mongo/s/sharding_mongod_test_fixture.h
@@ -33,29 +33,19 @@
 #include "mongo/db/service_context.h"
 #include "mongo/db/service_context_d_test_fixture.h"
 #include "mongo/executor/network_test_env.h"
+#include "mongo/s/grid.h"
 #include "mongo/unittest/unittest.h"
 
 namespace mongo {
 
-class BalancerConfiguration;
-class CatalogCache;
 class CatalogCacheLoader;
 class ConnectionString;
-class ClusterCursorManager;
 class DistLockCatalog;
 class DistLockManager;
 class NamespaceString;
 class RemoteCommandTargeterFactoryMock;
-class ShardingCatalogClient;
 class ShardRegistry;
 
-namespace executor {
-class NetworkInterfaceMock;
-class NetworkTestEnv;
-class TaskExecutor;
-class TaskExecutorPool;
-}  // namespace executor
-
 namespace repl {
 class ReplicationCoordinatorMock;
 class ReplSettings;
diff --git a/src/mongo/s/sharding_task_executor.cpp b/src/mongo/s/sharding_task_executor.cpp
new file mode 100644
index 00000000000..45c3407c6d1
--- /dev/null
+++ b/src/mongo/s/sharding_task_executor.cpp
@@ -0,0 +1,207 @@
+/**
+ *    Copyright (C) 2017 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#define MONGO_LOG_DEFAULT_COMPONENT mongo::logger::LogComponent::kSharding
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/s/sharding_task_executor.h"
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/status_with.h"
+#include "mongo/bson/timestamp.h"
+#include "mongo/db/logical_time.h"
+#include "mongo/db/operation_time_tracker.h"
+#include "mongo/executor/thread_pool_task_executor.h"
+#include "mongo/rpc/get_status_from_command_result.h"
+#include "mongo/rpc/metadata/sharding_metadata.h"
+#include "mongo/s/client/shard_registry.h"
+#include "mongo/s/cluster_last_error_info.h"
+#include "mongo/s/grid.h"
+#include "mongo/util/log.h"
+#include "mongo/util/scopeguard.h"
+
+namespace mongo {
+namespace executor {
+
+namespace {
+const std::string kOperationTimeField = "operationTime";
+}
+
+ShardingTaskExecutor::ShardingTaskExecutor(std::unique_ptr<ThreadPoolTaskExecutor> executor)
+    : _executor(std::move(executor)) {}
+
+void ShardingTaskExecutor::startup() {
+    _executor->startup();
+}
+
+void ShardingTaskExecutor::shutdown() {
+    _executor->shutdown();
+}
+
+void ShardingTaskExecutor::join() {
+    _executor->join();
+}
+
+void ShardingTaskExecutor::appendDiagnosticBSON(mongo::BSONObjBuilder* builder) const {
+    _executor->appendDiagnosticBSON(builder);
+}
+
+Date_t ShardingTaskExecutor::now() {
+    return _executor->now();
+}
+
+StatusWith<TaskExecutor::EventHandle> ShardingTaskExecutor::makeEvent() {
+    return _executor->makeEvent();
+}
+
+void ShardingTaskExecutor::signalEvent(const EventHandle& event) {
+    return _executor->signalEvent(event);
+}
+
+StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::onEvent(const EventHandle& event,
+                                                                       const CallbackFn& work) {
+    return _executor->onEvent(event, work);
+}
+
+void ShardingTaskExecutor::waitForEvent(const EventHandle& event) {
+    _executor->waitForEvent(event);
+}
+
+StatusWith<stdx::cv_status> ShardingTaskExecutor::waitForEvent(OperationContext* opCtx,
+                                                               const EventHandle& event,
+                                                               Date_t deadline) {
+    return _executor->waitForEvent(opCtx, event, deadline);
+}
+
+StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::scheduleWork(
+    const CallbackFn& work) {
+    return _executor->scheduleWork(work);
+}
+
+StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::scheduleWorkAt(
+    Date_t when, const CallbackFn& work) {
+    return _executor->scheduleWorkAt(when, work);
+}
+
+StatusWith<TaskExecutor::CallbackHandle> ShardingTaskExecutor::scheduleRemoteCommand(
+    const RemoteCommandRequest& request, const RemoteCommandCallbackFn& cb) {
+
+    // schedule the user's callback if there is not opCtx
+    if (!request.opCtx) {
+        return _executor->scheduleRemoteCommand(request, cb);
+    }
+
+    boost::optional<RemoteCommandRequest> newRequest;
+
+    if (request.opCtx->getLogicalSessionId() && !request.cmdObj.hasField("lsid")) {
+        newRequest.emplace(request);
+        BSONObjBuilder bob(std::move(newRequest->cmdObj));
+        {
+            BSONObjBuilder subbob(bob.subobjStart("lsid"));
+            request.opCtx->getLogicalSessionId()->serialize(&subbob);
+        }
+
+        newRequest->cmdObj = bob.obj();
+    }
+
+    std::shared_ptr<OperationTimeTracker> timeTracker = OperationTimeTracker::get(request.opCtx);
+
+    auto clusterGLE = ClusterLastErrorInfo::get(request.opCtx->getClient());
+
+    auto shardingCb = [timeTracker, clusterGLE, cb](
+        const TaskExecutor::RemoteCommandCallbackArgs& args) {
+        ON_BLOCK_EXIT([&cb, &args]() { cb(args); });
+
+        // Update replica set monitor info.
+        auto shard = grid.shardRegistry()->getShardForHostNoReload(args.request.target);
+        if (!shard) {
+            LOG(1) << "Could not find shard containing host: " << args.request.target.toString();
+        }
+
+        if (!args.response.isOK()) {
+            if (shard) {
+                shard->updateReplSetMonitor(args.request.target, args.response.status);
+            }
+            LOG(1) << "Error processing the remote request, not updating operationTime or gLE";
+            return;
+        }
+
+        if (shard) {
+            shard->updateReplSetMonitor(args.request.target,
+                                        getStatusFromCommandResult(args.response.data));
+        }
+
+        // Update the logical clock.
+        invariant(timeTracker);
+        auto operationTime = args.response.data[kOperationTimeField];
+        if (!operationTime.eoo()) {
+            invariant(operationTime.type() == BSONType::bsonTimestamp);
+            timeTracker->updateOperationTime(LogicalTime(operationTime.timestamp()));
+        }
+
+        // Update getLastError info for the client if we're tracking it.
+        if (clusterGLE) {
+            auto swShardingMetadata =
+                rpc::ShardingMetadata::readFromMetadata(args.response.metadata);
+            if (swShardingMetadata.isOK()) {
+                auto shardingMetadata = std::move(swShardingMetadata.getValue());
+
+                auto shardConn = ConnectionString::parse(args.request.target.toString());
+                if (!shardConn.isOK()) {
+                    severe() << "got bad host string in saveGLEStats: " << args.request.target;
+                }
+
+                clusterGLE->addHostOpTime(shardConn.getValue(),
+                                          HostOpTime(shardingMetadata.getLastOpTime(),
+                                                     shardingMetadata.getLastElectionId()));
+            } else if (swShardingMetadata.getStatus() != ErrorCodes::NoSuchKey) {
+                warning() << "Got invalid sharding metadata "
+                          << redact(swShardingMetadata.getStatus()) << " metadata object was '"
+                          << redact(args.response.metadata) << "'";
+            }
+        }
+    };
+
+    return _executor->scheduleRemoteCommand(newRequest ? *newRequest : request, shardingCb);
+}
+
+void ShardingTaskExecutor::cancel(const CallbackHandle& cbHandle) {
+    _executor->cancel(cbHandle);
+}
+
+void ShardingTaskExecutor::wait(const CallbackHandle& cbHandle) {
+    _executor->wait(cbHandle);
+}
+
+void ShardingTaskExecutor::appendConnectionStats(ConnectionPoolStats* stats) const {
+    _executor->appendConnectionStats(stats);
+}
+
+}  // namespace executor
+}  // namespace mongo
diff --git a/src/mongo/s/sharding_task_executor.h b/src/mongo/s/sharding_task_executor.h
new file mode 100644
index 00000000000..4c2571c684a
--- /dev/null
+++ b/src/mongo/s/sharding_task_executor.h
@@ -0,0 +1,82 @@
+/**
+ *    Copyright (C) 2017 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <memory>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/status_with.h"
+#include "mongo/executor/task_executor.h"
+#include "mongo/stdx/condition_variable.h"
+#include "mongo/stdx/list.h"
+#include "mongo/stdx/mutex.h"
+
+namespace mongo {
+namespace executor {
+
+struct ConnectionPoolStats;
+class ThreadPoolTaskExecutor;
+
+/**
+ * Implementation of a TaskExecutor that uses ThreadPoolTaskExecutor to submit tasks and allows to
+ * override methods if needed.
+ */
+class ShardingTaskExecutor final : public TaskExecutor {
+    MONGO_DISALLOW_COPYING(ShardingTaskExecutor);
+
+public:
+    ShardingTaskExecutor(std::unique_ptr<ThreadPoolTaskExecutor> executor);
+
+    void startup() override;
+    void shutdown() override;
+    void join() override;
+    void appendDiagnosticBSON(BSONObjBuilder* builder) const override;
+    Date_t now() override;
+    StatusWith<EventHandle> makeEvent() override;
+    void signalEvent(const EventHandle& event) override;
+    StatusWith<CallbackHandle> onEvent(const EventHandle& event, const CallbackFn& work) override;
+    void waitForEvent(const EventHandle& event) override;
+    StatusWith<stdx::cv_status> waitForEvent(OperationContext* opCtx,
+                                             const EventHandle& event,
+                                             Date_t deadline) override;
+    StatusWith<CallbackHandle> scheduleWork(const CallbackFn& work) override;
+    StatusWith<CallbackHandle> scheduleWorkAt(Date_t when, const CallbackFn& work) override;
+    StatusWith<CallbackHandle> scheduleRemoteCommand(const RemoteCommandRequest& request,
+                                                     const RemoteCommandCallbackFn& cb) override;
+    void cancel(const CallbackHandle& cbHandle) override;
+    void wait(const CallbackHandle& cbHandle) override;
+
+    void appendConnectionStats(ConnectionPoolStats* stats) const override;
+
+private:
+    std::unique_ptr<ThreadPoolTaskExecutor> _executor;
+};
+
+}  // namespace executor
+}  // namespace mongo
diff --git a/src/mongo/s/sharding_test_fixture.cpp b/src/mongo/s/sharding_test_fixture.cpp
index 235054b36c1..b33a434c637 100644
--- a/src/mongo/s/sharding_test_fixture.cpp
+++ b/src/mongo/s/sharding_test_fixture.cpp
@@ -44,7 +44,6 @@
 #include "mongo/db/query/collation/collator_factory_mock.h"
 #include "mongo/db/query/query_request.h"
 #include "mongo/db/repl/read_concern_args.h"
-#include "mongo/db/s/sharding_task_executor.h"
 #include "mongo/db/service_context_noop.h"
 #include "mongo/executor/network_interface_mock.h"
 #include "mongo/executor/task_executor_pool.h"
@@ -66,6 +65,7 @@
 #include "mongo/s/query/cluster_cursor_manager.h"
 #include "mongo/s/request_types/set_shard_version_request.h"
 #include "mongo/s/sharding_egress_metadata_hook_for_mongos.h"
+#include "mongo/s/sharding_task_executor.h"
 #include "mongo/s/write_ops/batched_command_response.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/transport/mock_session.h"
diff --git a/src/mongo/s/sharding_uptime_reporter.cpp b/src/mongo/s/sharding_uptime_reporter.cpp
index 0b4a1ff9e5e..3fa5a96fc27 100644
--- a/src/mongo/s/sharding_uptime_reporter.cpp
+++ b/src/mongo/s/sharding_uptime_reporter.cpp
@@ -35,7 +35,6 @@
 #include "mongo/db/client.h"
 #include "mongo/db/server_options.h"
 #include "mongo/s/balancer_configuration.h"
-#include "mongo/s/catalog/sharding_catalog_client.h"
 #include "mongo/s/catalog/type_mongos.h"
 #include "mongo/s/grid.h"
 #include "mongo/util/concurrency/idle_thread_block.h"
diff --git a/src/mongo/transport/service_state_machine_test.cpp b/src/mongo/transport/service_state_machine_test.cpp
index 1a065e24e38..d74fcbcdfc7 100644
--- a/src/mongo/transport/service_state_machine_test.cpp
+++ b/src/mongo/transport/service_state_machine_test.cpp
@@ -33,6 +33,7 @@
 #include "mongo/base/checked_cast.h"
 #include "mongo/bson/bsonobj.h"
 #include "mongo/bson/bsonobjbuilder.h"
+#include "mongo/db/client.h"
 #include "mongo/db/dbmessage.h"
 #include "mongo/db/service_context_noop.h"
 #include "mongo/stdx/memory.h"
@@ -52,7 +53,8 @@
 
 namespace mongo {
 namespace {
-inline std::string stateToString(ServiceStateMachine::State state) {
+
+std::string stateToString(ServiceStateMachine::State state) {
     std::string ret = str::stream() << state;
     return ret;
 }
diff --git a/src/mongo/util/signal_handlers.cpp b/src/mongo/util/signal_handlers.cpp
index ed84a273b91..26eee867369 100644
--- a/src/mongo/util/signal_handlers.cpp
+++ b/src/mongo/util/signal_handlers.cpp
@@ -41,6 +41,7 @@
 
 #include "mongo/db/log_process_details.h"
 #include "mongo/db/server_options.h"
+#include "mongo/db/service_context.h"
 #include "mongo/platform/process_id.h"
 #include "mongo/stdx/thread.h"
 #include "mongo/util/assert_util.h"
-- 
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