Merge pull request #1333 from baranowb/UNDERTOW-2072

[UNDERTOW-2072] DefaultByteBufferPool.getBuffer() may return null

Author: fl4via

core/src/main/java/io/undertow/server/DefaultByteBufferPool.java

@@ -139,6 +139,7 @@ public PooledByteBuffer allocate() {
             buffer = queue.poll();
             if (buffer != null) {
                 currentQueueLengthUpdater.decrementAndGet(this);
+                //buffer.clear();
             }
         }
         if (buffer == null) {
@@ -259,20 +260,23 @@ private static class DefaultPooledBuffer implements PooledByteBuffer {
 
         @Override
         public ByteBuffer getBuffer() {
-            if(referenceCount == 0) {
+            final ByteBuffer tmp = this.buffer;
+            //UNDERTOW-2072
+            if (referenceCount == 0 || tmp == null) {
                 throw UndertowMessages.MESSAGES.bufferAlreadyFreed();
             }
-            return buffer;
+            return tmp;
         }
 
         @Override
         public void close() {
-            if(referenceCountUpdater.compareAndSet(this, 1, 0)) {
-                if(leakDetector != null) {
+            final ByteBuffer tmp = this.buffer;
+            if (referenceCountUpdater.compareAndSet(this, 1, 0)) {
+                this.buffer = null;
+                if (leakDetector != null) {
                     leakDetector.closed = true;
                 }
-                pool.freeInternal(buffer);
-                this.buffer = null;
+                pool.freeInternal(tmp);
             }
         }