From 1c3da8681b394ce3b14fb44e27cb682c045d5f92 Mon Sep 17 00:00:00 2001
From: Arnaud Giersch <arnaud.giersch@iut-bm.univ-fcomte.fr>
Date: Mon, 23 May 2011 14:57:56 +0200
Subject: [PATCH 1/1] Use a lock-free synchronized queue for the message queue.

---
 messages.cpp | 39 ++++++++++++++++++++++-----------------
 messages.h   |  3 ++-
 2 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/messages.cpp b/messages.cpp
index f5df396..025871a 100644
--- a/messages.cpp
+++ b/messages.cpp
@@ -28,41 +28,46 @@ double message::get_size() const
 
 void message_queue::push(m_task_t task)
 {
-    mutex.acquire();
-    queue.push(task);
-    cond.signal();
-    mutex.release();
+    if (queue.push(task)) {
+         // list was empty, the push must be signaled
+        mutex.acquire();
+        cond.signal();
+        mutex.release();
+    }
 }
 
 bool message_queue::pop(message*& msg, m_host_t& from, double timeout)
 {
-    if (timeout != 0) {
-        volatile double deadline =
-            timeout > 0 ? MSG_get_clock() + timeout : 0.0;
+    m_task_t task;
+    if (!queue.try_pop(task)) {
+        if (timeout == 0.0)
+            return false;
+
         mutex.acquire();
-        while (queue.empty() && (!deadline || deadline > MSG_get_clock())) {
+        if (!queue.try_pop(task)) {
             xbt_ex_t e;
             XBT_DEBUG("waiting for a message to come");
             TRY {
-                if (deadline)
-                    cond.timedwait(mutex, deadline - MSG_get_clock());
+                if (timeout > 0)
+                    cond.timedwait(mutex, timeout);
                 else
                     cond.wait(mutex);
             }
+            TRY_CLEANUP {
+                mutex.release();
+            }
             CATCH (e) {
                 if (e.category != timeout_error)
                     RETHROW;
                 xbt_ex_free(e);
+                return false;   // got a timeout
             }
+            bool pop_was_successful = queue.try_pop(task);
+            xbt_assert(pop_was_successful);
+        } else {
+            mutex.release();
         }
-        mutex.release();
     }
-
-    if (queue.empty())
-        return false;
-
-    m_task_t task = queue.front();
-    queue.pop();
     msg = static_cast<message*>(MSG_task_get_data(task));
     from = MSG_task_get_source(task);
     MSG_task_destroy(task);
diff --git a/messages.h b/messages.h
index 605b3be..8de464a 100644
--- a/messages.h
+++ b/messages.h
@@ -5,6 +5,7 @@
 #include <string>
 #include <msg/msg.h>
 #include "synchro.h"
+#include "sync_queue.h"
 
 class message {
 public:
@@ -39,7 +40,7 @@ public:
 private:
     mutex_t mutex;
     condition_t cond;
-    std::queue<m_task_t> queue;
+    sync_queue<m_task_t> queue;
 };
 
 #endif // !MESSAGES_H
-- 
2.39.5