From d6a9d6adde4ee478b6b7664590ef2fe4e1410db8 Mon Sep 17 00:00:00 2001
From: Olivier Goffart <olivier.goffart@nokia.com>
Date: Wed, 2 Feb 2011 11:31:20 +0100
Subject: Fix QMutex can deadlock when calling tryLock

in the unix code, if the QMutexPrivate::wait() with a timeout
expires in the same moment that the mutex is released,  wakeup
would be set, but would be then ignored. (reset to false
quickly after)

If we waken up between the timeout and the re-aquisition of
the internal mutex, we consider that the mutex has been locked.

Reviewed-by: brad
Task-number: QTBUG-16115
(cherry picked from commit 7987d4cfd3ce86c20a55b5661a5221f12246b27e)
---
 src/corelib/thread/qmutex_unix.cpp |  5 ++++-
 tests/auto/qmutex/tst_qmutex.cpp   | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/src/corelib/thread/qmutex_unix.cpp b/src/corelib/thread/qmutex_unix.cpp
index b04fd67..4eb9750 100644
--- a/src/corelib/thread/qmutex_unix.cpp
+++ b/src/corelib/thread/qmutex_unix.cpp
@@ -94,8 +94,11 @@ bool QMutexPrivate::wait(int timeout)
             errorCode = pthread_cond_timedwait(&cond, &mutex, &ti);
         }
         if (errorCode) {
-            if (errorCode == ETIMEDOUT)
+            if (errorCode == ETIMEDOUT) {
+                if (wakeup)
+                    errorCode = 0;
                 break;
+            }
             report_error(errorCode, "QMutex::lock()", "cv wait");
         }
     }
diff --git a/tests/auto/qmutex/tst_qmutex.cpp b/tests/auto/qmutex/tst_qmutex.cpp
index a7c615a..68d3692 100644
--- a/tests/auto/qmutex/tst_qmutex.cpp
+++ b/tests/auto/qmutex/tst_qmutex.cpp
@@ -67,6 +67,7 @@ private slots:
     void lock_unlock_locked_tryLock();
     void stressTest();
     void tryLockRace();
+    void qtbug16115_trylock();
 };
 
 static const int iterations = 100;
@@ -464,5 +465,42 @@ void tst_QMutex::tryLockRace()
     TryLockRaceThread::mutex.unlock();
 }
 
+static volatile int qtbug16115_trylock_counter;
+
+void tst_QMutex::qtbug16115_trylock()
+{
+    //Used to deadlock on unix
+    struct TrylockThread : QThread {
+        TrylockThread(QMutex &mut) : mut(mut) {}
+        QMutex &mut;
+        void run() {
+            for (int i = 0; i < 1000000; ++i) {
+                if (mut.tryLock(0)) {
+                    Q_ASSERT((++qtbug16115_trylock_counter) == 1);
+                    Q_ASSERT((--qtbug16115_trylock_counter) == 0);
+                    mut.unlock();
+                }
+            }
+        }
+    };
+    QMutex mut;
+    TrylockThread t1(mut);
+    TrylockThread t2(mut);
+    TrylockThread t3(mut);
+    t1.start();
+    t2.start();
+    t3.start();
+
+    for (int i = 0; i < 1000000; ++i) {
+        mut.lock();
+        Q_ASSERT((++qtbug16115_trylock_counter) == 1);
+        Q_ASSERT((--qtbug16115_trylock_counter) == 0);
+        mut.unlock();
+    }
+    t1.wait();
+    t2.wait();
+    t3.wait();
+}
+
 QTEST_MAIN(tst_QMutex)
 #include "tst_qmutex.moc"
-- 
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