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eae801ba TR |
1 | // futex -*- C++ -*- |
2 | ||
8d9254fc | 3 | // Copyright (C) 2015-2020 Free Software Foundation, Inc. |
eae801ba TR |
4 | // |
5 | // This file is part of the GNU ISO C++ Library. This library is free | |
6 | // software; you can redistribute it and/or modify it under the | |
7 | // terms of the GNU General Public License as published by the | |
8 | // Free Software Foundation; either version 3, or (at your option) | |
9 | // any later version. | |
10 | ||
11 | // This library is distributed in the hope that it will be useful, | |
12 | // but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | // GNU General Public License for more details. | |
15 | ||
16 | // Under Section 7 of GPL version 3, you are granted additional | |
17 | // permissions described in the GCC Runtime Library Exception, version | |
18 | // 3.1, as published by the Free Software Foundation. | |
19 | ||
20 | // You should have received a copy of the GNU General Public License and | |
21 | // a copy of the GCC Runtime Library Exception along with this program; | |
22 | // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see | |
23 | // <http://www.gnu.org/licenses/>. | |
24 | ||
eae801ba | 25 | #include <bits/atomic_futex.h> |
8ba7f29e | 26 | #ifdef _GLIBCXX_HAS_GTHREADS |
1e3919ac | 27 | #if defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1 |
eae801ba TR |
28 | #include <chrono> |
29 | #include <climits> | |
30 | #include <syscall.h> | |
31 | #include <unistd.h> | |
32 | #include <sys/time.h> | |
33 | #include <errno.h> | |
34 | #include <debug/debug.h> | |
35 | ||
36 | // Constants for the wait/wake futex syscall operations | |
37 | const unsigned futex_wait_op = 0; | |
5bad23ce MC |
38 | const unsigned futex_wait_bitset_op = 9; |
39 | const unsigned futex_clock_realtime_flag = 256; | |
40 | const unsigned futex_bitset_match_any = ~0; | |
eae801ba TR |
41 | const unsigned futex_wake_op = 1; |
42 | ||
5bad23ce MC |
43 | namespace |
44 | { | |
45 | std::atomic<bool> futex_clock_realtime_unavailable; | |
46 | } | |
47 | ||
eae801ba TR |
48 | namespace std _GLIBCXX_VISIBILITY(default) |
49 | { | |
50 | _GLIBCXX_BEGIN_NAMESPACE_VERSION | |
51 | ||
52 | bool | |
53 | __atomic_futex_unsigned_base::_M_futex_wait_until(unsigned *__addr, | |
54 | unsigned __val, | |
55 | bool __has_timeout, chrono::seconds __s, chrono::nanoseconds __ns) | |
56 | { | |
57 | if (!__has_timeout) | |
58 | { | |
59 | // Ignore whether we actually succeeded to block because at worst, | |
60 | // we will fall back to spin-waiting. The only thing we could do | |
61 | // here on errors is abort. | |
62 | int ret __attribute__((unused)); | |
55089c2b | 63 | ret = syscall (SYS_futex, __addr, futex_wait_op, __val, nullptr); |
9fbd2e55 | 64 | __glibcxx_assert(ret == 0 || errno == EINTR || errno == EAGAIN); |
eae801ba TR |
65 | return true; |
66 | } | |
67 | else | |
68 | { | |
5bad23ce MC |
69 | if (!futex_clock_realtime_unavailable.load(std::memory_order_relaxed)) |
70 | { | |
71 | struct timespec rt; | |
72 | rt.tv_sec = __s.count(); | |
73 | rt.tv_nsec = __ns.count(); | |
74 | if (syscall (SYS_futex, __addr, | |
75 | futex_wait_bitset_op | futex_clock_realtime_flag, | |
76 | __val, &rt, nullptr, futex_bitset_match_any) == -1) | |
77 | { | |
78 | __glibcxx_assert(errno == EINTR || errno == EAGAIN | |
79 | || errno == ETIMEDOUT || errno == ENOSYS); | |
80 | if (errno == ETIMEDOUT) | |
81 | return false; | |
82 | if (errno == ENOSYS) | |
83 | { | |
84 | futex_clock_realtime_unavailable.store(true, | |
85 | std::memory_order_relaxed); | |
86 | // Fall through to legacy implementation if the system | |
87 | // call is unavailable. | |
88 | } | |
89 | else | |
90 | return true; | |
91 | } | |
92 | else | |
93 | return true; | |
94 | } | |
95 | ||
96 | // We only get to here if futex_clock_realtime_unavailable was | |
97 | // true or has just been set to true. | |
eae801ba TR |
98 | struct timeval tv; |
99 | gettimeofday (&tv, NULL); | |
100 | // Convert the absolute timeout value to a relative timeout | |
101 | struct timespec rt; | |
102 | rt.tv_sec = __s.count() - tv.tv_sec; | |
103 | rt.tv_nsec = __ns.count() - tv.tv_usec * 1000; | |
104 | if (rt.tv_nsec < 0) | |
105 | { | |
106 | rt.tv_nsec += 1000000000; | |
107 | --rt.tv_sec; | |
108 | } | |
109 | // Did we already time out? | |
110 | if (rt.tv_sec < 0) | |
111 | return false; | |
112 | ||
113 | if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1) | |
114 | { | |
9fbd2e55 JW |
115 | __glibcxx_assert(errno == EINTR || errno == EAGAIN |
116 | || errno == ETIMEDOUT); | |
eae801ba TR |
117 | if (errno == ETIMEDOUT) |
118 | return false; | |
119 | } | |
120 | return true; | |
121 | } | |
122 | } | |
123 | ||
124 | void | |
125 | __atomic_futex_unsigned_base::_M_futex_notify_all(unsigned* __addr) | |
126 | { | |
127 | // This syscall can fail for various reasons, including in situations | |
128 | // in which there is no real error. Thus, we don't bother checking | |
129 | // the error codes. See the futex documentation and glibc for background. | |
130 | syscall (SYS_futex, __addr, futex_wake_op, INT_MAX); | |
131 | } | |
132 | ||
8dcf3d3c | 133 | _GLIBCXX_END_NAMESPACE_VERSION |
eae801ba | 134 | } |
8ba7f29e JW |
135 | #endif // defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1 |
136 | #endif // _GLIBCXX_HAS_GTHREADS |