ConsumerImpl optimization - use atomic value for queueHasMessages.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk/qpid@778452 13f79535-47bb-0310-9956-ffa450edef68

2 files changed, 11 insertions, 19 deletions

diff --git a/cpp/src/qpid/broker/SemanticState.cpp b/cpp/src/qpid/broker/SemanticState.cpp
index 22908afd8e..8f918ff40f 100644
--- a/cpp/src/qpid/broker/SemanticState.cpp
+++ b/cpp/src/qpid/broker/SemanticState.cpp
@@ -257,7 +257,7 @@ SemanticState::ConsumerImpl::ConsumerImpl(SemanticState* _parent,
     msgCredit(0), 
     byteCredit(0),
     notifyEnabled(true),
-    queueHasMessages(true),
+    queueHasMessages(1),
     syncFrequency(_arguments.getAsInt("qpid.sync_frequency")),
     deliveryCount(0) {}
 
@@ -593,18 +593,11 @@ bool SemanticState::ConsumerImpl::hasOutput() {
 
 bool SemanticState::ConsumerImpl::doOutput()
 {
-    {
-        Mutex::ScopedLock l(lock);
-        if (!haveCredit() || !queueHasMessages) return false;
-        queueHasMessages = false;
-    }
-    bool moreMessages = queue->dispatch(shared_from_this());
-    {
-        Mutex::ScopedLock l(lock);
-        // queueHasMessages may have been set by a notify() during dispatch()
-        queueHasMessages = queueHasMessages || moreMessages;
-    }
-    return queueHasMessages;
+    if (!haveCredit() || !queueHasMessages.boolCompareAndSwap(1, 0))
+        return false;
+    if (queue->dispatch(shared_from_this()))
+        queueHasMessages.boolCompareAndSwap(0, 1);
+    return queueHasMessages.get();
 }
 
 void SemanticState::ConsumerImpl::enableNotify()
@@ -626,10 +619,8 @@ bool SemanticState::ConsumerImpl::isNotifyEnabled() const {
 
 void SemanticState::ConsumerImpl::notify()
 {
-    {
-        Mutex::ScopedLock l(lock);
-        queueHasMessages = true;
-    }
+    queueHasMessages.boolCompareAndSwap(0, 1);
+
     //TODO: alter this, don't want to hold locks across external
     //calls; for now its is required to protect the notify() from
     //having part of the object chain of the invocation being
diff --git a/cpp/src/qpid/broker/SemanticState.h b/cpp/src/qpid/broker/SemanticState.h
index 8237f22e3f..a69962c083 100644
--- a/cpp/src/qpid/broker/SemanticState.h
+++ b/cpp/src/qpid/broker/SemanticState.h
@@ -77,8 +77,9 @@ class SemanticState : public sys::OutputTask,
         uint32_t msgCredit;
         uint32_t byteCredit;
         bool notifyEnabled;
-        //        sys::AtomicValue<bool> queueHasMessages;
-        bool queueHasMessages;
+        // queueHasMessages is boolean but valgrind has trouble with
+        // AtomicValue<bool> so use an int with 1 or 0.
+        sys:: AtomicValue<int> queueHasMessages; 
         const int syncFrequency;
         int deliveryCount;