From bb67941a1ba9c04a58bc4cb74cfd02ec9f315024 Mon Sep 17 00:00:00 2001
From: Cheahuychou Mao <cheahuychou.mao@mongodb.com>
Date: Wed, 25 Mar 2020 13:59:23 -0400
Subject: SERVER-47141 Make failpoint in NetworkInterfaceTL sort targets before
 constructing CommandState

---
 jstests/sharding/hedged_reads.js            | 17 ++++++------
 src/mongo/executor/network_interface_tl.cpp | 40 +++++++++++++----------------
 2 files changed, 27 insertions(+), 30 deletions(-)

diff --git a/jstests/sharding/hedged_reads.js b/jstests/sharding/hedged_reads.js
index 9cf05016615..288f0d4d60a 100644
--- a/jstests/sharding/hedged_reads.js
+++ b/jstests/sharding/hedged_reads.js
@@ -94,15 +94,15 @@ st.rs0.nodes.forEach(function(conn) {
 assert.commandWorked(
     st.s.adminCommand({setParameter: 1, logComponentVerbosity: {network: {verbosity: 2}}}));
 
-jsTest.log("Verify the initial request is canceled when the hedged request responds first");
+jsTest.log("Verify that the initial request is canceled when the hedged request responds first");
 try {
     // Make the initial request block.
-    setCommandDelay(sortedNodes[0], "find", kLargeTimeoutMS);
+    setCommandDelay(sortedNodes[0], "count", kLargeTimeoutMS);
 
     const comment = "test_kill_initial_request_" + ObjectId();
     assert.commandWorked(testDB.runCommand({
-        find: collName,
-        filter: {x: {$gte: 0}},
+        count: collName,
+        query: {x: {$gte: 0}},
         $readPreference: {mode: "nearest"},
         comment: comment
     }));
@@ -117,18 +117,19 @@ try {
     clearCommandDelay(sortedNodes[0]);
 }
 
-jsTest.log("Verify the additional request is canceled when the initial request responds first");
+jsTest.log(
+    "Verify that the additional request is canceled when the initial request responds first");
 try {
     // Make the additional/hedged request block, set a large maxTimeMSForHedgedReads to prevent
     // the remote host from killing the operation by itself.
     assert.commandWorked(
         st.s.adminCommand({setParameter: 1, maxTimeMSForHedgedReads: kLargeTimeoutMS}));
-    setCommandDelay(sortedNodes[1], "find", kLargeTimeoutMS);
+    setCommandDelay(sortedNodes[1], "count", kLargeTimeoutMS);
 
     const comment = "test_kill_additional_request_" + ObjectId();
     assert.commandWorked(testDB.runCommand({
-        find: collName,
-        filter: {x: {$gte: 0}},
+        count: collName,
+        query: {x: {$gte: 0}},
         $readPreference: {mode: "nearest"},
         comment: comment
     }));
diff --git a/src/mongo/executor/network_interface_tl.cpp b/src/mongo/executor/network_interface_tl.cpp
index fcae4dee869..3f2f6871c3d 100644
--- a/src/mongo/executor/network_interface_tl.cpp
+++ b/src/mongo/executor/network_interface_tl.cpp
@@ -419,6 +419,18 @@ Status NetworkInterfaceTL::startCommand(const TaskExecutor::CallbackHandle& cbHa
         request.metadata = newMetadata.obj();
     }
 
+    bool targetHostsInAlphabeticalOrder =
+        MONGO_unlikely(networkInterfaceSendRequestsToTargetHostsInAlphabeticalOrder.shouldFail());
+
+    if (targetHostsInAlphabeticalOrder) {
+        // Sort the target hosts by host names.
+        std::sort(request.target.begin(),
+                  request.target.end(),
+                  [](const HostAndPort& target1, const HostAndPort& target2) {
+                      return target1.toString() < target2.toString();
+                  });
+    }
+
     auto [cmdState, future] = CommandState::make(this, request, cbHandle);
     if (cmdState->requestOnAny.timeout != cmdState->requestOnAny.kNoTimeout) {
         cmdState->deadline = cmdState->stopwatch.start() + cmdState->requestOnAny.timeout;
@@ -487,37 +499,21 @@ Status NetworkInterfaceTL::startCommand(const TaskExecutor::CallbackHandle& cbHa
 
     RequestManager* rm = cmdState->requestManager.get();
 
-    if (MONGO_unlikely(networkInterfaceSendRequestsToTargetHostsInAlphabeticalOrder.shouldFail())) {
-        // Sort the target hosts by host names.
-        std::sort(request.target.begin(),
-                  request.target.end(),
-                  [](const HostAndPort& target1, const HostAndPort& target2) {
-                      return target1.toString() < target2.toString();
-                  });
-    }
-
     // Attempt to get a connection to every target host
     for (size_t idx = 0; idx < request.target.size() && !rm->usedAllConn(); ++idx) {
         auto connFuture = _pool->get(request.target[idx], request.sslMode, request.timeout);
 
-        if (connFuture.isReady()) {
+        // If connection future is ready or requests should be sent in order, send the request
+        // immediately.
+        if (connFuture.isReady() || targetHostsInAlphabeticalOrder) {
             rm->trySend(std::move(connFuture).getNoThrow(), idx);
             continue;
         }
 
-        if (MONGO_unlikely(
-                networkInterfaceSendRequestsToTargetHostsInAlphabeticalOrder.shouldFail())) {
-            // Wait for a connection so the requests are sent to target hosts in alphabetical order
-            // of host names.
-            auto swConn = std::move(connFuture).get();
+        // Otherwise, schedule the request.
+        std::move(connFuture).thenRunOn(_reactor).getAsync([requestStates, rm, idx](auto swConn) {
             rm->trySend(std::move(swConn), idx);
-        } else {
-            // For every connection future we didn't have immediately ready, schedule
-            std::move(connFuture)
-                .thenRunOn(_reactor)
-                .getAsync(
-                    [requestStates, rm, idx](auto swConn) { rm->trySend(std::move(swConn), idx); });
-        }
+        });
     }
 
     return Status::OK();
-- 
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