SERVER-23609 Introduce RAII class for retrieving sharding cache objects

Around the sharding code there are a lot of repeated code sequences, where
we first check for existence of the database, then get the chunk manager.
In an effort to reduce this code duplication and to eventually be able to
get rid of the shared pointer references, this change introduces RAII
objects similar to the ones we have in mongod.

1 files changed, 109 insertions, 0 deletions

diff --git a/src/mongo/s/sharding_raii.cpp b/src/mongo/s/sharding_raii.cpp
new file mode 100644
index 00000000000..caacb4de8a8
--- /dev/null
+++ b/src/mongo/s/sharding_raii.cpp
@@ -0,0 +1,109 @@
+/**
+ *    Copyright (C) 2016 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.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/s/sharding_raii.h"
+
+#include "mongo/base/status_with.h"
+#include "mongo/s/catalog/catalog_cache.h"
+#include "mongo/s/catalog/catalog_manager.h"
+#include "mongo/s/chunk_manager.h"
+#include "mongo/s/grid.h"
+
+namespace mongo {
+
+using std::shared_ptr;
+
+ScopedShardDatabase::ScopedShardDatabase(std::shared_ptr<DBConfig> db) : _db(db) {
+    invariant(_db);
+}
+
+ScopedShardDatabase::~ScopedShardDatabase() = default;
+
+StatusWith<ScopedShardDatabase> ScopedShardDatabase::getExisting(OperationContext* txn,
+                                                                 StringData dbName) {
+    auto dbStatus = Grid::get(txn)->catalogCache()->getDatabase(txn, dbName.toString());
+    if (!dbStatus.isOK()) {
+        return {dbStatus.getStatus().code(),
+                str::stream() << "Database " << dbName << " was not found due to "
+                              << dbStatus.getStatus().toString()};
+    }
+
+    return {ScopedShardDatabase(std::move(dbStatus.getValue()))};
+}
+
+StatusWith<ScopedShardDatabase> ScopedShardDatabase::getOrCreate(OperationContext* txn,
+                                                                 StringData dbName) {
+    auto dbStatus = getExisting(txn, dbName);
+    if (dbStatus.isOK()) {
+        return dbStatus;
+    }
+
+    if (dbStatus == ErrorCodes::NamespaceNotFound) {
+        auto statusCreateDb =
+            Grid::get(txn)->catalogManager(txn)->createDatabase(txn, dbName.toString());
+        if (statusCreateDb.isOK() || statusCreateDb == ErrorCodes::NamespaceExists) {
+            return getExisting(txn, dbName);
+        }
+
+        return statusCreateDb;
+    }
+
+    return dbStatus.getStatus();
+}
+
+ScopedChunkManager::ScopedChunkManager(ScopedShardDatabase db, std::shared_ptr<ChunkManager> cm)
+    : _db(std::move(db)), _cm(std::move(cm)) {}
+
+ScopedChunkManager::~ScopedChunkManager() = default;
+
+StatusWith<ScopedChunkManager> ScopedChunkManager::getExisting(OperationContext* txn,
+                                                               const NamespaceString& nss) {
+    auto scopedDbStatus = ScopedShardDatabase::getExisting(txn, nss.db());
+    if (!scopedDbStatus.isOK()) {
+        return scopedDbStatus.getStatus();
+    }
+
+    auto scopedDb = std::move(scopedDbStatus.getValue());
+
+    shared_ptr<ChunkManager> cm = scopedDb.db()->getChunkManagerIfExists(txn, nss.ns(), true);
+    if (!cm) {
+        return {ErrorCodes::NamespaceNotSharded,
+                str::stream() << "Collection " << nss.ns() << " does not exist or is not sharded."};
+    }
+
+    if (cm->getChunkMap().empty()) {
+        return {ErrorCodes::NamespaceNotSharded,
+                str::stream() << "Collection " << nss.ns() << " does not have any chunks."};
+    }
+
+    return {ScopedChunkManager(std::move(scopedDb), std::move(cm))};
+}
+
+}  // namespace mongo