Change Async buffer returning logic to only watch reads when necessary

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@810591 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 21 insertions, 3 deletions

diff --git a/qpid/cpp/src/qpid/sys/posix/AsynchIO.cpp b/qpid/cpp/src/qpid/sys/posix/AsynchIO.cpp
index 5d1ac6d034..e702a6d76d 100644
--- a/qpid/cpp/src/qpid/sys/posix/AsynchIO.cpp
+++ b/qpid/cpp/src/qpid/sys/posix/AsynchIO.cpp
@@ -305,6 +305,13 @@ private:
      * thread processing this handle.
      */
     volatile bool writePending;
+    /**
+     * This records whether we've been reading is flow controlled:
+     * it's safe as a simple boolean as the only way to be stopped
+     * is in calls only allowed in the callback context, the only calls
+     * checking it are also in calls only allowed in callback context.
+     */
+    volatile bool readingStopped;
 };
 
 AsynchIO::AsynchIO(const Socket& s,
@@ -323,7 +330,8 @@ AsynchIO::AsynchIO(const Socket& s,
     idleCallback(iCb),
     socket(s),
     queuedClose(false),
-    writePending(false) {
+    writePending(false),
+    readingStopped(false) {
 
     s.setNonblocking();
 }
@@ -351,8 +359,11 @@ void AsynchIO::queueReadBuffer(BufferBase* buff) {
     assert(buff);
     buff->dataStart = 0;
     buff->dataCount = 0;
+
+    bool queueWasEmpty = bufferQueue.empty();
     bufferQueue.push_back(buff);
-    DispatchHandle::rewatchRead();
+    if (queueWasEmpty && !readingStopped)
+        DispatchHandle::rewatchRead();
 }
 
 void AsynchIO::unread(BufferBase* buff) {
@@ -361,8 +372,11 @@ void AsynchIO::unread(BufferBase* buff) {
         memmove(buff->bytes, buff->bytes+buff->dataStart, buff->dataCount);
         buff->dataStart = 0;
     }
+
+    bool queueWasEmpty = bufferQueue.empty();
     bufferQueue.push_front(buff);
-    DispatchHandle::rewatchRead();
+    if (queueWasEmpty && !readingStopped)
+        DispatchHandle::rewatchRead();
 }
 
 void AsynchIO::queueWrite(BufferBase* buff) {
@@ -378,6 +392,7 @@ void AsynchIO::queueWrite(BufferBase* buff) {
     DispatchHandle::rewatchWrite();
 }
 
+// This can happen outside the callback context
 void AsynchIO::notifyPendingWrite() {
     writePending = true;
     DispatchHandle::rewatchWrite();
@@ -392,11 +407,14 @@ bool AsynchIO::writeQueueEmpty() {
     return writeQueue.empty();
 }
 
+// This can happen outside the callback context
 void AsynchIO::startReading() {
+    readingStopped = false;
     DispatchHandle::rewatchRead();
 }
 
 void AsynchIO::stopReading() {
+    readingStopped = true;
     DispatchHandle::unwatchRead();
 }