summaryrefslogtreecommitdiffstats
path: root/src/corelib/thread/qmutex_linux.cpp
blob: 1bb5e77e7794ea63b974f4980b8e81993a320ba5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
/****************************************************************************
**
** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** GNU Lesser General Public License Usage
** This file may be used under the terms of the GNU Lesser General Public
** License version 2.1 as published by the Free Software Foundation and
** appearing in the file LICENSE.LGPL included in the packaging of this
** file. Please review the following information to ensure the GNU Lesser
** General Public License version 2.1 requirements will be met:
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU General
** Public License version 3.0 as published by the Free Software Foundation
** and appearing in the file LICENSE.GPL included in the packaging of this
** file. Please review the following information to ensure the GNU General
** Public License version 3.0 requirements will be met:
** http://www.gnu.org/copyleft/gpl.html.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms and
** conditions contained in a signed written agreement between you and Nokia.
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include "qplatformdefs.h"
#include "qmutex.h"

#ifndef QT_NO_THREAD
#include "qatomic.h"
#include "qmutex_p.h"
#include "qelapsedtimer.h"

#include <linux/futex.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <errno.h>

#ifndef QT_LINUX_FUTEX
# error "Qt build is broken: qmutex_linux.cpp is being built but futex support is not wanted"
#endif

QT_BEGIN_NAMESPACE

static inline int futexFlags()
{
    int value = 0;
#if defined(FUTEX_PRIVATE_FLAG)
    // check if the kernel supports extra futex flags
    // FUTEX_PRIVATE_FLAG appeared in v2.6.22
    static QBasicAtomicInt futexFlagSupport = Q_BASIC_ATOMIC_INITIALIZER(-1);

    value = futexFlagSupport.load();
    if (value == -1) {
        // try an operation that has no side-effects: wake up 42 threads
        // futex will return -1 (errno==ENOSYS) if the flag isn't supported
        // there should be no other error conditions
        value = syscall(SYS_futex, &futexFlagSupport,
                        FUTEX_WAKE | FUTEX_PRIVATE_FLAG,
                        42, 0, 0, 0);
        if (value != -1) {
            value = FUTEX_PRIVATE_FLAG;
            futexFlagSupport.store(value);
            return value;
        }
        value = 0;
        futexFlagSupport.store(value);
    }
#endif
    return value;
}

static inline int _q_futex(void *addr, int op, int val, const struct timespec *timeout)
{
    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;

    return syscall(SYS_futex, int_addr, op | futexFlags(), val, timeout, addr2, val2);
}

static inline QMutexData *dummyFutexValue()
{
    return reinterpret_cast<QMutexData *>(quintptr(3));
}

bool QBasicMutex::lockInternal(int timeout)
{
    QElapsedTimer elapsedTimer;
    if (timeout >= 1)
        elapsedTimer.start();

    while (!fastTryLock()) {
        QMutexData *d = d_ptr.load();
        if (!d) // if d is 0, the mutex is unlocked
            continue;

        if (quintptr(d) <= 0x3) { //d == dummyLocked() || d == dummyFutexValue()
            if (timeout == 0)
                return false;
            while (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) != 0) {
                struct timespec ts, *pts = 0;
                if (timeout >= 1) {
                    // recalculate the timeout
                    qint64 xtimeout = 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);
                    pts = &ts;
                }
                int r = _q_futex(&d_ptr, FUTEX_WAIT, quintptr(dummyFutexValue()), pts);
                if (r != 0 && errno == ETIMEDOUT)
                    return false;
            }
            return true;
        }
        Q_ASSERT(d->recursive);
        return static_cast<QRecursiveMutexPrivate *>(d)->lock(timeout);
    }
    Q_ASSERT(d_ptr.load());
    return true;
}

void QBasicMutex::unlockInternal()
{
    QMutexData *d = d_ptr.load();
    Q_ASSERT(d); //we must be locked
    Q_ASSERT(d != dummyLocked()); // testAndSetRelease(dummyLocked(), 0) failed

    if (d == dummyFutexValue()) {
        d_ptr.fetchAndStoreRelease(0);
        _q_futex(&d_ptr, FUTEX_WAKE, 1, 0);
        return;
    }

    Q_ASSERT(d->recursive);
    static_cast<QRecursiveMutexPrivate *>(d)->unlock();
}


QT_END_NAMESPACE

#endif // QT_NO_THREAD