Revert "Fixing the race condition in event dispatcher implementation on"

This reverts commit 5f21450a61ba2459e6dc5b08b236b15a067bf81f.

It's the wrong fix for the problem. The socket operations in the
select thread are not supposed to be thread safe. It is thread safe
between the select thread and the caller thread, but not if there are
more than one caller thread. Ensuring complete thread safety would
probably require fixes in other areas as well.

The correct fix is for the client to ensure that calls to the socket
registering functions are either serialized or contained within one
thread.

Task:     QT-3358
RevBy:    Aleksandar Sasha Babic

2 files changed, 10 insertions, 56 deletions

diff --git a/src/corelib/kernel/qeventdispatcher_symbian.cpp b/src/corelib/kernel/qeventdispatcher_symbian.cpp
index d00a623..826caf2 100644
--- a/src/corelib/kernel/qeventdispatcher_symbian.cpp
+++ b/src/corelib/kernel/qeventdispatcher_symbian.cpp
@@ -100,40 +100,25 @@ static inline int qt_socket_select(int nfds, fd_set *readfds, fd_set *writefds,
 class QSelectMutexGrabber
 {
 public:
-    QSelectMutexGrabber(int fd, QMutex *threadMutex, QMutex *selectCallMutex)
-        : m_threadMutex(threadMutex), m_selectCallMutex(selectCallMutex), bHasThreadLock(false)
+    QSelectMutexGrabber(int fd, QMutex *mutex)
+        : m_mutex(mutex)
     {
-        // see if selectThread is waiting m_waitCond
-        // if yes ... dont write to pipe
-        if (m_threadMutex->tryLock()) {
-            bHasThreadLock = true;
+        if (m_mutex->tryLock())
             return;
-        }
-
-        // still check that SelectThread
-        // is in select call
-        if (m_selectCallMutex->tryLock()) {
-            m_selectCallMutex->unlock();
-            return;
-        }
 
         char dummy = 0;
         qt_pipe_write(fd, &dummy, 1);
 
-        m_threadMutex->lock();
-        bHasThreadLock = true;
+        m_mutex->lock();
     }
 
     ~QSelectMutexGrabber()
     {
-        if(bHasThreadLock)
-            m_threadMutex->unlock();
+        m_mutex->unlock();
     }
 
 private:
-    QMutex *m_threadMutex;
-    QMutex *m_selectCallMutex;
-    bool bHasThreadLock;
+    QMutex *m_mutex;
 };
 
 /*
@@ -415,12 +400,7 @@ void QSelectThread::run()
 
         int ret;
         int savedSelectErrno;
-        {
-            // helps fighting the race condition between
-            // selctthread and new socket requests (cancel, restart ...)
-            QMutexLocker locker(&m_selectCallMutex);
-            ret = qt_socket_select(maxfd, &readfds, &writefds, &exceptionfds, 0);
-        }
+        ret = qt_socket_select(maxfd, &readfds, &writefds, &exceptionfds, 0);
         savedSelectErrno = errno;
 
         char buffer;
@@ -515,9 +495,7 @@ void QSelectThread::requestSocketEvents ( QSocketNotifier *notifier, TRequestSta
         start();
     }
 
-    QMutexLocker locker(&m_grabberMutex);
-
-    QSelectMutexGrabber lock(m_pipeEnds[1], &m_mutex, &m_selectCallMutex);
+    QSelectMutexGrabber lock(m_pipeEnds[1], &m_mutex);
 
     Q_ASSERT(!m_AOStatuses.contains(notifier));
 
@@ -528,9 +506,7 @@ void QSelectThread::requestSocketEvents ( QSocketNotifier *notifier, TRequestSta
 
 void QSelectThread::cancelSocketEvents ( QSocketNotifier *notifier )
 {
-    QMutexLocker locker(&m_grabberMutex);
-
-    QSelectMutexGrabber lock(m_pipeEnds[1], &m_mutex, &m_selectCallMutex);
+    QSelectMutexGrabber lock(m_pipeEnds[1], &m_mutex);
 
     m_AOStatuses.remove(notifier);
 
@@ -539,9 +515,7 @@ void QSelectThread::cancelSocketEvents ( QSocketNotifier *notifier )
 
 void QSelectThread::restart()
 {
-    QMutexLocker locker(&m_grabberMutex);
-
-    QSelectMutexGrabber lock(m_pipeEnds[1], &m_mutex, &m_selectCallMutex);
+    QSelectMutexGrabber lock(m_pipeEnds[1], &m_mutex);
 
     m_waitCond.wakeAll();
 }
diff --git a/src/corelib/kernel/qeventdispatcher_symbian_p.h b/src/corelib/kernel/qeventdispatcher_symbian_p.h
index 7021314..8a9c9a0 100644
--- a/src/corelib/kernel/qeventdispatcher_symbian_p.h
+++ b/src/corelib/kernel/qeventdispatcher_symbian_p.h
@@ -211,26 +211,6 @@ private:
     QMutex m_mutex;
     QWaitCondition m_waitCond;
     bool m_quit;
-
-    // to protect when several
-    // requests like:
-    // requestSocketEvents
-    // cancelSocketEvents
-    // kick in the same time
-    // all will fight for m_mutex
-    //
-    // TODO: fix more elegantely
-    //
-    QMutex m_grabberMutex;
-
-    // this one will tell
-    // if selectthread is
-    // really in select call
-    // and will prevent
-    // writing to pipe that
-    // causes later in locking
-    // of the thread in waitcond
-    QMutex m_selectCallMutex;
 };
 
 class Q_CORE_EXPORT CQtActiveScheduler : public CActiveScheduler