Move the futex implementation to a header

So I can use it in QSemaphore and provide a Windows implementation.

Change-Id: I6e9274c1e7444ad48c81fffd14dbc0a8e2201302
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/thread/qfutex_p.h

@@ -0,0 +1,128 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 Intel Corporation.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QFUTEX_P_H
+#define QFUTEX_P_H
+
+#include <qglobal.h>
+
+QT_BEGIN_NAMESPACE
+
+namespace QtDummyFutex {
+    Q_DECL_CONSTEXPR inline bool futexAvailable() { return false; }
+    template <typename Atomic>
+    inline bool futexWait(Atomic &, typename Atomic::Type, int = 0)
+    { Q_UNREACHABLE(); return false; }
+    template <typename Atomic> inline void futexWakeOne(Atomic &)
+    { Q_UNREACHABLE(); }
+    template <typename Atomic> inline void futexWakeAll(Atomic &)
+    { Q_UNREACHABLE(); }
+}
+
+QT_END_NAMESPACE
+
+#if defined(Q_OS_LINUX) && !defined(QT_LINUXBASE)
+// use Linux mutexes everywhere except for LSB builds
+#  include <sys/syscall.h>
+#  include <errno.h>
+#  include <limits.h>
+#  include <unistd.h>
+#  include <asm/unistd.h>
+#  include <linux/futex.h>
+#  define QT_ALWAYS_USE_FUTEX
+
+// if not defined in linux/futex.h
+#  define FUTEX_PRIVATE_FLAG        128         // added in v2.6.22
+
+QT_BEGIN_NAMESPACE
+namespace QtLinuxFutex {
+    constexpr inline bool futexAvailable() { return true; }
+    inline int _q_futex(int *addr, int op, int val, const struct timespec *timeout) Q_DECL_NOTHROW
+    {
+        int *addr2 = 0;
+        int val2 = 0;
+
+        // we use __NR_futex because some libcs (like Android's bionic) don't
+        // provide SYS_futex etc.
+        return syscall(__NR_futex, addr, op | FUTEX_PRIVATE_FLAG, val, timeout, addr2, val2);
+    }
+    template <typename T> int *addr(T *ptr)
+    {
+        int *int_addr = reinterpret_cast<int *>(ptr);
+#if Q_BYTE_ORDER == Q_BIG_ENDIAN
+        if (sizeof(T) > sizeof(int))
+            int_addr++; //We want a pointer to the least significant half
+#endif
+        return int_addr;
+    }
+
+    template <typename Atomic>
+    inline void futexWait(Atomic &futex, typename Atomic::Type expectedValue)
+    {
+        _q_futex(addr(&futex), FUTEX_WAIT, qintptr(expectedValue), nullptr);
+    }
+    template <typename Atomic>
+    inline bool futexWait(Atomic &futex, typename Atomic::Type expectedValue, qint64 nstimeout)
+    {
+        struct timespec ts;
+        ts.tv_sec = nstimeout / 1000 / 1000 / 1000;
+        ts.tv_nsec = nstimeout % (1000 * 1000 * 1000);
+        int r = _q_futex(addr(&futex), FUTEX_WAIT, qintptr(expectedValue), &ts);
+        return r == 0 || errno != ETIMEDOUT;
+    }
+    template <typename Atomic> inline void futexWakeOne(Atomic &futex)
+    {
+        _q_futex(addr(&futex), FUTEX_WAKE, 1, nullptr);
+    }
+    template <typename Atomic> inline void futexWakeAll(Atomic &futex)
+    {
+        _q_futex(addr(&futex), FUTEX_WAKE, INT_MAX, nullptr);
+    }
+}
+namespace QtFutex = QtLinuxFutex;
+QT_END_NAMESPACE
+
+#else
+
+QT_BEGIN_NAMESPACE
+namespace QtFutex = QtDummyFutex;
+QT_END_NAMESPACE
+#endif
+
+#endif // QFUTEX_P_H

src/corelib/thread/qmutex_linux.cpp

@@ -44,15 +44,9 @@
 #ifndef QT_NO_THREAD
 #include "qatomic.h"
 #include "qmutex_p.h"
-#include "qelapsedtimer.h"
+#include "qfutex_p.h"
 
-#include <linux/futex.h>
-#include <sys/syscall.h>
-#include <unistd.h>
-#include <errno.h>
-#include <asm/unistd.h>
-
-#ifndef QT_LINUX_FUTEX
+#ifndef QT_ALWAYS_USE_FUTEX
 # error "Qt build is broken: qmutex_linux.cpp is being built but futex support is not wanted"
 #endif
 
@@ -63,6 +57,8 @@
 
 QT_BEGIN_NAMESPACE
 
+using namespace QtFutex;
+
 /*
  * QBasicMutex implementation on Linux with futexes
  *
@@ -107,20 +103,6 @@ QT_BEGIN_NAMESPACE
  * waiting in the past. We then set the mutex to 0x0 and perform a FUTEX_WAKE.
  */
 
-static inline int _q_futex(void *addr, int op, int val, const struct timespec *timeout) Q_DECL_NOTHROW
-{
-    volatile int *int_addr = reinterpret_cast<volatile int *>(addr);
-#if Q_BYTE_ORDER == Q_BIG_ENDIAN && QT_POINTER_SIZE == 8
-    int_addr++; //We want a pointer to the 32 least significant bit of QMutex::d
-#endif
-    int *addr2 = 0;
-    int val2 = 0;
-
-    // we use __NR_futex because some libcs (like Android's bionic) don't
-    // provide SYS_futex etc.
-    return syscall(__NR_futex, int_addr, op | FUTEX_PRIVATE_FLAG, val, timeout, addr2, val2);
-}
-
 static inline QMutexData *dummyFutexValue()
 {
     return reinterpret_cast<QMutexData *>(quintptr(3));
@@ -136,36 +118,38 @@ bool lockInternal_helper(QBasicAtomicPointer<QMutexData> &d_ptr, int timeout = -
     if (timeout == 0)
         return false;
 
-    struct timespec ts, *pts = 0;
-    if (IsTimed && timeout > 0) {
-        ts.tv_sec = timeout / 1000;
-        ts.tv_nsec = (timeout % 1000) * 1000 * 1000;
-    }
-
     // the mutex is locked already, set a bit indicating we're waiting
-    while (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) != 0) {
-        if (IsTimed && pts == &ts) {
-            // recalculate the timeout
-            qint64 xtimeout = qint64(timeout) * 1000 * 1000;
-            xtimeout -= elapsedTimer->nsecsElapsed();
-            if (xtimeout <= 0) {
-                // timer expired after we returned
-                return false;
-            }
-            ts.tv_sec = xtimeout / Q_INT64_C(1000) / 1000 / 1000;
-            ts.tv_nsec = xtimeout % (Q_INT64_C(1000) * 1000 * 1000);
-        }
-        if (IsTimed && timeout > 0)
-            pts = &ts;
+    if (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) == nullptr)
+        return true;
 
+    qint64 nstimeout = timeout * Q_INT64_C(1000) * 1000;
+    qint64 remainingTime = nstimeout;
+    forever {
         // successfully set the waiting bit, now sleep
-        int r = _q_futex(&d_ptr, FUTEX_WAIT, quintptr(dummyFutexValue()), pts);
-        if (IsTimed && r != 0 && errno == ETIMEDOUT)
-            return false;
+        if (IsTimed && nstimeout >= 0) {
+            bool r = futexWait(d_ptr, dummyFutexValue(), remainingTime);
+            if (!r)
+                return false;
 
-        // we got woken up, so try to acquire the mutex
-        // note we must set to dummyFutexValue because there could be other threads
-        // also waiting
+            // we got woken up, so try to acquire the mutex
+            // note we must set to dummyFutexValue because there could be other threads
+            // also waiting
+            if (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) == nullptr)
+                return true;
+
+            // recalculate the timeout
+            remainingTime = nstimeout - elapsedTimer->nsecsElapsed();
+            if (remainingTime <= 0)
+                return false;
+        } else {
+            futexWait(d_ptr, dummyFutexValue());
+
+            // we got woken up, so try to acquire the mutex
+            // note we must set to dummyFutexValue because there could be other threads
+            // also waiting
+            if (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) == nullptr)
+                return true;
+        }
     }
 
     Q_ASSERT(d_ptr.load());
@@ -195,10 +179,9 @@ void QBasicMutex::unlockInternal() Q_DECL_NOTHROW
     Q_ASSERT(!isRecursive());
 
     d_ptr.storeRelease(0);
-    _q_futex(&d_ptr, FUTEX_WAKE, 1, 0);
+    futexWakeOne(d_ptr);
 }
 
-
 QT_END_NAMESPACE
 
 #endif // QT_NO_THREAD

src/corelib/thread/thread.pri

@@ -22,6 +22,7 @@ HEADERS += thread/qmutex.h \
 # private headers
 HEADERS += thread/qmutex_p.h \
            thread/qmutexpool_p.h \
+           thread/qfutex_p.h \
            thread/qfutureinterface_p.h \
            thread/qfuturewatcher_p.h \
            thread/qorderedmutexlocker_p.h \