qmutex_unix: use a semaphore when available

It makes tst_QMutex::contendedQMutex with no msleep 8 times faster

Change-Id: Ic300e7618b4467e4e08b30f0213bd23c06d4d90a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/thread/qmutex_p.h

@@ -55,11 +55,14 @@
 
 #if defined(Q_OS_MAC)
 # include <mach/semaphore.h>
-#endif
+#elif defined(Q_OS_LINUX) && !defined(QT_LINUXBASE)
-
-#if defined(Q_OS_LINUX) && !defined(QT_LINUXBASE)
 // use Linux mutexes everywhere except for LSB builds
 #  define QT_LINUX_FUTEX
+#elif defined(Q_OS_UNIX)
+# if _POSIX_VERSION-0 >= 200112L || _XOPEN_VERSION-0 >= 600
+#  include <semaphore.h>
+#  define QT_UNIX_SEMAPHORE
+# endif
 #endif
 
 struct timespec;
@@ -120,6 +123,8 @@ public:
     //platform specific stuff
 #if defined(Q_OS_MAC)
     semaphore_t mach_semaphore;
+#elif defined(QT_UNIX_SEMAPHORE)
+    sem_t semaphore;
 #elif defined(Q_OS_UNIX)
     bool wakeup;
     pthread_mutex_t mutex;

src/corelib/thread/qmutex_unix.cpp

@@ -1,6 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2015 The Qt Company Ltd.
+** Copyright (C) 2015 Olivier Goffart <ogoffart@woboq.com>
 ** Contact: http://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -42,6 +43,7 @@
 #include <errno.h>
 #include <sys/time.h>
 #include <time.h>
+#include "private/qcore_unix_p.h"
 
 #if defined(Q_OS_VXWORKS) && defined(wakeup)
 #undef wakeup
@@ -55,6 +57,51 @@ static void report_error(int code, const char *where, const char *what)
         qWarning("%s: %s failure: %s", where, what, qPrintable(qt_error_string(code)));
 }
 
+#ifdef QT_UNIX_SEMAPHORE
+
+QMutexPrivate::QMutexPrivate()
+{
+    report_error(sem_init(&semaphore, 0, 0), "QMutex", "sem_init");
+}
+
+QMutexPrivate::~QMutexPrivate()
+{
+
+    report_error(sem_destroy(&semaphore), "QMutex", "sem_destroy");
+}
+
+bool QMutexPrivate::wait(int timeout)
+{
+    int errorCode;
+    if (timeout < 0) {
+        do {
+            errorCode = sem_wait(&semaphore);
+        } while (errorCode && errno == EINTR);
+        report_error(errorCode, "QMutex::lock()", "sem_wait");
+    } else {
+        timespec ts;
+        report_error(clock_gettime(CLOCK_REALTIME, &ts), "QMutex::lock()", "clock_gettime");
+        ts.tv_sec += timeout / 1000;
+        ts.tv_nsec += timeout % 1000 * Q_UINT64_C(1000) * 1000;
+        normalizedTimespec(ts);
+        do {
+            errorCode = sem_timedwait(&semaphore, &ts);
+        } while (errorCode && errno == EINTR);
+
+        if (errorCode && errno == ETIMEDOUT)
+            return false;
+        report_error(errorCode, "QMutex::lock()", "sem_timedwait");
+    }
+    return true;
+}
+
+void QMutexPrivate::wakeUp() Q_DECL_NOTHROW
+{
+    report_error(sem_post(&semaphore), "QMutex::unlock", "sem_post");
+}
+
+#else // QT_UNIX_SEMAPHORE
+
 QMutexPrivate::QMutexPrivate()
     : wakeup(false)
 {
@@ -103,6 +150,7 @@ void QMutexPrivate::wakeUp() Q_DECL_NOTHROW
     report_error(pthread_mutex_unlock(&mutex), "QMutex::unlock", "mutex unlock");
 }
 
+#endif
 
 QT_END_NAMESPACE