From ed5d40386e04fd75ea8051102abcb3a1f1f53ddd Mon Sep 17 00:00:00 2001
From: Alan Conway <aconway@apache.org>
Date: Thu, 7 Aug 2008 13:45:24 +0000
Subject: Patch from Gordon Sim to fix issues with hasOutput implementation.

git-svn-id: https://svn.apache.org/repos/asf/incubator/qpid/trunk/qpid@683617 13f79535-47bb-0310-9956-ffa450edef68
---
 cpp/src/qpid/broker/Queue.cpp         | 25 +++++++++++++++++++++++--
 cpp/src/qpid/broker/Queue.h           | 12 ++++++++----
 cpp/src/qpid/broker/SemanticState.cpp |  3 +--
 3 files changed, 32 insertions(+), 8 deletions(-)

(limited to 'cpp/src')

diff --git a/cpp/src/qpid/broker/Queue.cpp b/cpp/src/qpid/broker/Queue.cpp
index 3b447e97f2..acab1e06f1 100644
--- a/cpp/src/qpid/broker/Queue.cpp
+++ b/cpp/src/qpid/broker/Queue.cpp
@@ -212,9 +212,30 @@ bool Queue::getNextMessage(QueuedMessage& m, Consumer& c)
     }
 }
 
-bool Queue::empty() const {
+bool Queue::checkForMessages(Consumer& c)
+{
     Mutex::ScopedLock locker(messageLock);
-    return messages.empty();
+    if (messages.empty()) {
+        //no message available, register consumer for notification
+        //when this changes
+        addListener(c);
+        return false;
+    } else {
+        QueuedMessage msg = messages.front();
+        if (store && !msg.payload->isEnqueueComplete()) {
+            //though a message is on the queue, it has not yet been
+            //enqueued and so is not available for consumption yet,
+            //register consumer for notification when this changes
+            addListener(c);
+            return false;            
+        } else {
+            //check that consumer has sufficient credit for the
+            //message (if it does not, no need to register it for
+            //notification as the consumer itself will handle the
+            //credit allocation required to change this condition).
+            return c.accept(msg.payload);
+        }
+    }
 }
 
 bool Queue::consumeNextMessage(QueuedMessage& m, Consumer& c)
diff --git a/cpp/src/qpid/broker/Queue.h b/cpp/src/qpid/broker/Queue.h
index e35b3ef7ee..347fc5cf9d 100644
--- a/cpp/src/qpid/broker/Queue.h
+++ b/cpp/src/qpid/broker/Queue.h
@@ -107,6 +107,7 @@ namespace qpid {
 
             void notify();
             void removeListener(Consumer&);
+            void addListener(Consumer&);
 
             bool isExcluded(boost::intrusive_ptr<Message>& msg);
 
@@ -114,8 +115,6 @@ namespace qpid {
             void popAndDequeue();
 
         public:
-            // FIXME aconway 2008-08-06: was private, verify if needed public.
-            void addListener(Consumer&);
 
             virtual void notifyDurableIOComplete();
             typedef boost::shared_ptr<Queue> shared_ptr;
@@ -128,9 +127,14 @@ namespace qpid {
                   management::Manageable* parent = 0);
             ~Queue();
 
-            bool empty() const;
-            
             bool dispatch(Consumer&);
+            /**
+             * Check whether there would be a message available for
+             * dispatch to this consumer. If not, the consumer will be
+             * notified of events that may have changed this
+             * situation.
+             */
+            bool checkForMessages(Consumer&);
 
             void create(const qpid::framing::FieldTable& settings);
             void configure(const qpid::framing::FieldTable& settings);
diff --git a/cpp/src/qpid/broker/SemanticState.cpp b/cpp/src/qpid/broker/SemanticState.cpp
index bf034a0559..4d5c4e7537 100644
--- a/cpp/src/qpid/broker/SemanticState.cpp
+++ b/cpp/src/qpid/broker/SemanticState.cpp
@@ -591,8 +591,7 @@ void SemanticState::reject(DeliveryId first, DeliveryId last)
 }
 
 bool SemanticState::ConsumerImpl::hasOutput() {
-    queue->addListener(*this);
-    return !queue->empty();
+    return queue->checkForMessages(*this);
 }
 
 bool SemanticState::ConsumerImpl::doOutput()
-- 
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