Fix CSHARP-454. RequestStart and RequestDone now hold the lock for less time to avoid deadlock.

Author: Robert Stam

Driver/Core/MongoServer.cs

@@ -993,23 +993,30 @@ public virtual void Reconnect()
         /// </summary>
         public virtual void RequestDone()
         {
+            int threadId = Thread.CurrentThread.ManagedThreadId;
+            MongoConnection connectionToRelease = null;
+
             lock (_serverLock)
             {
-                int threadId = Thread.CurrentThread.ManagedThreadId;
                 Request request;
                 if (_requests.TryGetValue(threadId, out request))
                 {
                     if (--request.NestingLevel == 0)
                     {
                         _requests.Remove(threadId);
-                        ReleaseConnection(request.Connection);
+                        connectionToRelease = request.Connection;
                     }
                 }
                 else
                 {
                     throw new InvalidOperationException("Thread is not in a request (did you call RequestStart?).");
                 }
             }
+
+            if (connectionToRelease != null)
+            {
+                connectionToRelease.ServerInstance.ReleaseConnection(connectionToRelease);
+            }
         }
 
         /// <summary>
@@ -1034,9 +1041,10 @@ public virtual IDisposable RequestStart(MongoDatabase initialDatabase)
         /// <returns>A helper object that implements IDisposable and calls <see cref="RequestDone"/> from the Dispose method.</returns>
         public virtual IDisposable RequestStart(MongoDatabase initialDatabase, bool slaveOk)
         {
+            int threadId = Thread.CurrentThread.ManagedThreadId;
+
             lock (_serverLock)
             {
-                int threadId = Thread.CurrentThread.ManagedThreadId;
                 Request request;
                 if (_requests.TryGetValue(threadId, out request))
                 {
@@ -1045,15 +1053,18 @@ public virtual IDisposable RequestStart(MongoDatabase initialDatabase, bool slav
                         throw new InvalidOperationException("A nested call to RequestStart with slaveOk false is not allowed when the original call to RequestStart was made with slaveOk true.");
                     }
                     request.NestingLevel++;
-                }
-                else
-                {
-                    var serverInstance = ChooseServerInstance(slaveOk);
-                    var connection = serverInstance.AcquireConnection(initialDatabase);
-                    request = new Request(connection, slaveOk);
-                    _requests.Add(threadId, request);
+                    return new RequestStartResult(this);
                 }
 
+            }
+
+            var serverInstance = ChooseServerInstance(slaveOk);
+            var connection = serverInstance.AcquireConnection(initialDatabase);
+
+            lock (_serverLock)
+            {
+                var request = new Request(connection, slaveOk);
+                _requests.Add(threadId, request);
                 return new RequestStartResult(this);
             }
         }
@@ -1068,9 +1079,10 @@ public virtual IDisposable RequestStart(MongoDatabase initialDatabase, bool slav
         /// <returns>A helper object that implements IDisposable and calls <see cref="RequestDone"/> from the Dispose method.</returns>
         public virtual IDisposable RequestStart(MongoDatabase initialDatabase, MongoServerInstance serverInstance)
         {
+            int threadId = Thread.CurrentThread.ManagedThreadId;
+
             lock (_serverLock)
             {
-                int threadId = Thread.CurrentThread.ManagedThreadId;
                 Request request;
                 if (_requests.TryGetValue(threadId, out request))
                 {
@@ -1079,15 +1091,17 @@ public virtual IDisposable RequestStart(MongoDatabase initialDatabase, MongoServ
                         throw new InvalidOperationException("The server instance passed to a nested call to RequestStart does not match the server instance of the current Request.");
                     }
                     request.NestingLevel++;
+                    return new RequestStartResult(this);
                 }
-                else
-                {
-                    var connection = serverInstance.AcquireConnection(initialDatabase);
-                    var slaveOk = serverInstance.IsSecondary;
-                    request = new Request(connection, slaveOk);
-                    _requests.Add(threadId, request);
-                }
+            }
 
+            var connection = serverInstance.AcquireConnection(initialDatabase);
+            var slaveOk = serverInstance.IsSecondary;
+
+            lock (_serverLock)
+            {
+                var request = new Request(connection, slaveOk);
+                _requests.Add(threadId, request);
                 return new RequestStartResult(this);
             }
         }