JAVA-2027: When ensuring minimum connection pool size, open the connection in addition to creating it. Otherwise, there's little benefit of ensuring the minimum size.

Author: jyemin

driver-core/src/main/com/mongodb/connection/DefaultConnectionPool.java

@@ -284,13 +284,21 @@ public synchronized void run() {
                         if (LOGGER.isDebugEnabled()) {
                             LOGGER.debug(format("Pruning pooled connections to %s", serverId.getAddress()));
                         }
-                        pool.prune();
+                        try {
+                            pool.prune();
+                        } catch (Exception e) {
+                            LOGGER.warn("Exception thrown while pruning connection pool", e);
+                        }
                     }
                     if (shouldEnsureMinSize()) {
                         if (LOGGER.isDebugEnabled()) {
                             LOGGER.debug(format("Ensuring minimum pooled connections to %s", serverId.getAddress()));
                         }
-                        pool.ensureMinSize(settings.getMinSize());
+                        try {
+                            pool.ensureMinSize(settings.getMinSize(), true);
+                        } catch (Exception e) {
+                            LOGGER.warn("Exception thrown while ensuring minimum pool size", e);
+                        }
                     }
                 }
             };
@@ -472,9 +480,12 @@ public UsageTrackingInternalConnectionItemFactory(final InternalConnectionFactor
         }
 
         @Override
-        public UsageTrackingInternalConnection create() {
+        public UsageTrackingInternalConnection create(final boolean initialize) {
             UsageTrackingInternalConnection internalConnection =
             new UsageTrackingInternalConnection(internalConnectionFactory.create(serverId), generation.get());
+            if (initialize) {
+                internalConnection.open();
+            }
             connectionPoolListener.connectionAdded(new ConnectionEvent(getId(internalConnection)));
             return internalConnection;
         }

driver-core/src/main/com/mongodb/internal/connection/ConcurrentPool.java

@@ -45,7 +45,7 @@ public class ConcurrentPool<T> implements Pool<T> {
      * @param <T>
      */
     public interface ItemFactory<T> {
-        T create();
+        T create(final boolean initialize);
 
         void close(T t);
 
@@ -129,7 +129,7 @@ public T get(final long timeout, final TimeUnit timeUnit) {
 
         T t = available.pollLast();
         if (t == null) {
-            t = createNewAndReleasePermitIfFailure();
+            t = createNewAndReleasePermitIfFailure(false);
         }
 
         return t;
@@ -150,18 +150,18 @@ public void prune() {
         }
     }
 
-    public void ensureMinSize(final int minSize) {
+    public void ensureMinSize(final int minSize, final boolean initialize) {
         while (getCount() < minSize) {
             if (!acquirePermit(10, TimeUnit.MILLISECONDS)) {
                 break;
             }
-            release(createNewAndReleasePermitIfFailure());
+            release(createNewAndReleasePermitIfFailure(initialize));
         }
     }
 
-    private T createNewAndReleasePermitIfFailure() {
+    private T createNewAndReleasePermitIfFailure(final boolean initialize) {
         try {
-            T newMember = itemFactory.create();
+            T newMember = itemFactory.create(initialize);
             if (newMember == null) {
                 throw new MongoInternalException("The factory for the pool created a null item");
             }

driver-core/src/main/com/mongodb/internal/connection/PowerOfTwoBufferPool.java

@@ -53,7 +53,7 @@ public PowerOfTwoBufferPool(final int highestPowerOfTwo) {
             powerOfTwoToPoolMap.put(i, new ConcurrentPool<ByteBuffer>(Integer.MAX_VALUE,
                                                                          new ConcurrentPool.ItemFactory<ByteBuffer>() {
                                                                              @Override
-                                                                             public ByteBuffer create() {
+                                                                             public ByteBuffer create(final boolean initialize) {
                                                                                  return createNew(size);
                                                                              }