From cc781622299a4de5af2fdde6bfc1e2eb42e1623a Mon Sep 17 00:00:00 2001
From: Alan Conway <aconway@apache.org>
Date: Thu, 11 Dec 2008 20:33:26 +0000
Subject: sys/PollableQueue: dispatch in batches, allow put-back.

git-svn-id: https://svn.apache.org/repos/asf/incubator/qpid/trunk/qpid@725802 13f79535-47bb-0310-9956-ffa450edef68
---
 cpp/src/qpid/sys/PollableQueue.h | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

(limited to 'cpp/src/qpid/sys')

diff --git a/cpp/src/qpid/sys/PollableQueue.h b/cpp/src/qpid/sys/PollableQueue.h
index 953d198fb0..7f11cc35a9 100644
--- a/cpp/src/qpid/sys/PollableQueue.h
+++ b/cpp/src/qpid/sys/PollableQueue.h
@@ -44,13 +44,13 @@ class Poller;
 template <class T>
 class PollableQueue {
   public:
+    typedef std::deque<T> Queue;
+
     /**
-     * Callback to process an item from the queue.
-     *
-     * @return If true the item is removed from the queue else it
-     * remains on the queue and the queue is stopped.
+     * Callback to process a batch of items from the queue.
+     * @param values to process, any items remaining after call are put back on the queue.
      */
-    typedef boost::function<bool (const T&)> Callback;
+    typedef boost::function<void (Queue& values)> Callback;
 
     /** When the queue is selected by the poller, values are passed to callback cb. */
     PollableQueue(const Callback& cb, const boost::shared_ptr<sys::Poller>& poller);
@@ -73,7 +73,6 @@ class PollableQueue {
     bool empty() { ScopedLock l(lock); return queue.empty(); }
     
   private:
-    typedef std::deque<T> Queue;
     typedef sys::Monitor::ScopedLock ScopedLock;
     typedef sys::Monitor::ScopedUnlock ScopedUnlock;
 
@@ -84,7 +83,7 @@ class PollableQueue {
     boost::shared_ptr<sys::Poller> poller;
     PollableCondition condition;
     DispatchHandle handle;
-    Queue queue;
+    Queue queue, batch;
     Thread dispatcher;
     bool stopped;
 };
@@ -117,21 +116,19 @@ template <class T> void PollableQueue<T>::push(const T& t) {
 }
 
 template <class T> void PollableQueue<T>::dispatch(sys::DispatchHandle& h) {
-    ScopedLock l(lock);     // Prevent concurrent push
-    assert(dispatcher.id() == 0 || dispatcher.id() == Thread::current().id());
+    ScopedLock l(lock);
+    assert(dispatcher.id() == 0);
     dispatcher = Thread::current();
     while (!stopped && !queue.empty()) {
-        T value = queue.front();
-        queue.pop_front();
-        bool ok = false;
-        {   // unlock to allow concurrent push or call to stop() in callback.
-            ScopedUnlock u(lock);
-            // FIXME aconway 2008-12-02: not exception safe if callback throws.
-            ok = callback(value);
+        assert(batch.empty());
+        batch.swap(queue);
+        {
+            ScopedUnlock u(lock);   // Allow concurrent push to queue.
+            callback(batch);
         }
-        if (!ok) { // callback cannot process value,  put it back.
-            queue.push_front(value);
-            stopped=true;
+        if (!batch.empty()) {
+            queue.insert(queue.begin(), batch.begin(), batch.end()); // put back unprocessed items.
+            batch.clear();
         }
     }
     dispatcher = Thread();
-- 
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