Make counting of active streams more robust

Author: markt-asf

java/org/apache/coyote/http2/Http2AsyncUpgradeHandler.java

@@ -157,7 +157,7 @@ void sendStreamReset(StreamStateMachine state, StreamException se) throws IOExce
                 boolean active = state.isActive();
                 state.sendReset();
                 if (active) {
-                    decrementActiveRemoteStreamCount();
+                    decrementActiveRemoteStreamCount(getStream(se.getStreamId()));
                 }
             }
 

java/org/apache/coyote/http2/Http2UpgradeHandler.java

@@ -290,8 +290,8 @@ protected void processStreamOnContainerThread(Stream stream) {
     }
 
 
-    protected void decrementActiveRemoteStreamCount() {
-        setConnectionTimeoutForStreamCount(activeRemoteStreamCount.decrementAndGet());
+    protected void decrementActiveRemoteStreamCount(Stream stream) {
+        setConnectionTimeoutForStreamCount(stream.decrementAndGetActiveRemoteStreamCount());
     }
 
 
@@ -598,7 +598,7 @@ void sendStreamReset(StreamStateMachine state, StreamException se) throws IOExce
                 boolean active = state.isActive();
                 state.sendReset();
                 if (active) {
-                    decrementActiveRemoteStreamCount();
+                    decrementActiveRemoteStreamCount(getStream(se.getStreamId()));
                 }
             }
             socketWrapper.write(true, rstFrame, 0, rstFrame.length);
@@ -825,7 +825,7 @@ void writeBody(Stream stream, ByteBuffer data, int len, boolean finished) throws
     protected void sentEndOfStream(Stream stream) {
         stream.sentEndOfStream();
         if (!stream.isActive()) {
-            decrementActiveRemoteStreamCount();
+            decrementActiveRemoteStreamCount(stream);
         }
     }
 
@@ -1208,7 +1208,7 @@ private int allocate(AbstractStream stream, int allocation) {
     }
 
 
-    private Stream getStream(int streamId) {
+    Stream getStream(int streamId) {
         Integer key = Integer.valueOf(streamId);
         AbstractStream result = streams.get(key);
         if (result instanceof Stream) {
@@ -1536,6 +1536,7 @@ public HeaderEmitter headersStart(int streamId, boolean headersEndStream) throws
             Stream stream = getStream(streamId, false);
             if (stream == null) {
                 stream = createRemoteStream(streamId);
+                activeRemoteStreamCount.incrementAndGet();
             }
             if (streamId < maxActiveRemoteStreamId) {
                 throw new ConnectionException(sm.getString("upgradeHandler.stream.old", Integer.valueOf(streamId),
@@ -1597,9 +1598,8 @@ public void headersEnd(int streamId, boolean endOfStream) throws Http2Exception
             Stream stream = (Stream) abstractNonZeroStream;
             if (stream.isActive()) {
                 if (stream.receivedEndOfHeaders()) {
-
-                    if (localSettings.getMaxConcurrentStreams() < activeRemoteStreamCount.incrementAndGet()) {
-                        decrementActiveRemoteStreamCount();
+                    if (localSettings.getMaxConcurrentStreams() < activeRemoteStreamCount.get()) {
+                        decrementActiveRemoteStreamCount(stream);
                         // Ignoring maxConcurrentStreams increases the overhead count
                         increaseOverheadCount(FrameType.HEADERS);
                         throw new StreamException(
@@ -1643,7 +1643,7 @@ public void receivedEndOfStream(int streamId) throws ConnectionException {
     private void receivedEndOfStream(Stream stream) throws ConnectionException {
         stream.receivedEndOfStream();
         if (!stream.isActive()) {
-            decrementActiveRemoteStreamCount();
+            decrementActiveRemoteStreamCount(stream);
         }
     }
 
@@ -1669,7 +1669,7 @@ public void reset(int streamId, long errorCode) throws Http2Exception {
             boolean active = stream.isActive();
             stream.receiveReset(errorCode);
             if (active) {
-                decrementActiveRemoteStreamCount();
+                decrementActiveRemoteStreamCount(stream);
             }
         }
     }

java/org/apache/coyote/http2/Stream.java

@@ -25,6 +25,7 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.Supplier;
@@ -88,6 +89,7 @@ class Stream extends AbstractNonZeroStream implements HeaderEmitter {
     private final StreamInputBuffer inputBuffer;
     private final StreamOutputBuffer streamOutputBuffer = new StreamOutputBuffer();
     private final Http2OutputBuffer http2OutputBuffer = new Http2OutputBuffer(coyoteResponse, streamOutputBuffer);
+    private final AtomicBoolean removedFromActiveCount = new AtomicBoolean(false);
 
     // State machine would be too much overhead
     private int headerState = HEADER_STATE_START;
@@ -838,6 +840,20 @@ public void setIncremental(boolean incremental) {
     }
 
 
+    int decrementAndGetActiveRemoteStreamCount() {
+        /*
+         * Protect against mis-counting of active streams. This method should only be called once per stream but since
+         * the count of active streams is used to enforce the maximum concurrent streams limit, make sure each stream is
+         * only removed from the active count exactly once.
+         */
+        if (removedFromActiveCount.compareAndSet(false, true)) {
+            return handler.activeRemoteStreamCount.decrementAndGet();
+        } else {
+            return handler.activeRemoteStreamCount.get();
+        }
+    }
+
+
     class StreamOutputBuffer implements HttpOutputBuffer, WriteBuffer.Sink {
 
         private final Lock writeLock = new ReentrantLock();

webapps/docs/changelog.xml

@@ -161,6 +161,10 @@
         <code>Connector</code> element, similar to the <code>Executor</code>
         element, for consistency. (remm)
       </update>
+      <fix>
+        Make counting of active HTTP/2 streams per connection more robust.
+        (markt)
+      </fix>
     </changelog>
   </subsection>
   <subsection name="Jasper">