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39
40#ifndef QFUTEX_P_H
41#define QFUTEX_P_H
42
43//
44// W A R N I N G
45// -------------
46//
47// This file is not part of the Qt API. It exists purely as an
48// implementation detail. This header file may change from version to
49// version without notice, or even be removed.
50//
51// We mean it.
52//
53
54#include <qglobal.h>
55
56QT_BEGIN_NAMESPACE
57
58namespace QtDummyFutex {
59 constexpr inline bool futexAvailable() { return false; }
60 template <typename Atomic>
61 inline bool futexWait(Atomic &, typename Atomic::Type, int = 0)
62 { Q_UNREACHABLE(); return false; }
63 template <typename Atomic> inline void futexWakeOne(Atomic &)
64 { Q_UNREACHABLE(); }
65 template <typename Atomic> inline void futexWakeAll(Atomic &)
66 { Q_UNREACHABLE(); }
67}
68
69QT_END_NAMESPACE
70
71#if defined(Q_OS_LINUX) && !defined(QT_LINUXBASE)
72// use Linux mutexes everywhere except for LSB builds
73# include <sys/syscall.h>
74# include <errno.h>
75# include <limits.h>
76# include <unistd.h>
77# include <asm/unistd.h>
78# include <linux/futex.h>
79# define QT_ALWAYS_USE_FUTEX
80
81// if not defined in linux/futex.h
82# define FUTEX_PRIVATE_FLAG 128 // added in v2.6.22
83
84# if (__has_feature(thread_sanitizer) || defined(__SANITIZE_THREAD__)) && __has_include(<sanitizer/tsan_interface.h>)
85# include <sanitizer/tsan_interface.h>
86inline void _q_tsan_acquire(void *addr, void *addr2)
87{
88 __tsan_acquire(addr);
89 if (addr2)
90 __tsan_acquire(addr2);
91}
92inline void _q_tsan_release(void *addr, void *addr2)
93{
94 if (addr2)
95 __tsan_release(addr2);
96 __tsan_release(addr);
97}
98# else
99inline void _q_tsan_acquire(void *, void *) {}
100inline void _q_tsan_release(void *, void *) {}
101# endif // __has_feature(thread_sanitizer) || defined(__SANITIZE_THREAD__)
102
103QT_BEGIN_NAMESPACE
104namespace QtLinuxFutex {
105 constexpr inline bool futexAvailable() { return true; }
106 inline int _q_futex(int *addr, int op, int val, quintptr val2 = 0,
107 int *addr2 = nullptr, int val3 = 0) noexcept
108 {
109 // A futex call ensures total ordering on the futex words
110 // (in either success or failure of the call). Instruct TSAN accordingly,
111 // as TSAN does not understand the futex(2) syscall.
112 _q_tsan_release(addr, addr2);
113
114 // we use __NR_futex because some libcs (like Android's bionic) don't
115 // provide SYS_futex etc.
116 int result = syscall(__NR_futex, addr, op | FUTEX_PRIVATE_FLAG, val, val2, addr2, val3);
117
118 _q_tsan_acquire(addr, addr2);
119
120 return result;
121 }
122 template <typename T> int *addr(T *ptr)
123 {
124 int *int_addr = reinterpret_cast<int *>(ptr);
125#if Q_BYTE_ORDER == Q_BIG_ENDIAN
126 if (sizeof(T) > sizeof(int))
127 int_addr++; //We want a pointer to the least significant half
128#endif
129 return int_addr;
130 }
131
132 template <typename Atomic>
133 inline void futexWait(Atomic &futex, typename Atomic::Type expectedValue)
134 {
135 _q_futex(addr(&futex), FUTEX_WAIT, qintptr(expectedValue));
136 }
137 template <typename Atomic>
138 inline bool futexWait(Atomic &futex, typename Atomic::Type expectedValue, qint64 nstimeout)
139 {
140 struct timespec ts;
141 ts.tv_sec = nstimeout / 1000 / 1000 / 1000;
142 ts.tv_nsec = nstimeout % (1000 * 1000 * 1000);
143 int r = _q_futex(addr(&futex), FUTEX_WAIT, qintptr(expectedValue), quintptr(&ts));
144 return r == 0 || errno != ETIMEDOUT;
145 }
146 template <typename Atomic> inline void futexWakeOne(Atomic &futex)
147 {
148 _q_futex(addr(&futex), FUTEX_WAKE, 1);
149 }
150 template <typename Atomic> inline void futexWakeAll(Atomic &futex)
151 {
152 _q_futex(addr(&futex), FUTEX_WAKE, INT_MAX);
153 }
154 template <typename Atomic> inline
155 void futexWakeOp(Atomic &futex1, int wake1, int wake2, Atomic &futex2, quint32 op)
156 {
157 _q_futex(addr(&futex1), FUTEX_WAKE_OP, wake1, wake2, addr(&futex2), op);
158 }
159}
160namespace QtFutex = QtLinuxFutex;
161QT_END_NAMESPACE
162
163#else
164
165QT_BEGIN_NAMESPACE
166namespace QtFutex = QtDummyFutex;
167QT_END_NAMESPACE
168#endif
169
170#endif // QFUTEX_P_H
171