futex.cc revision 1.1.1.1 
1// futex -*- C++ -*-
2
3// Copyright (C) 2015 Free Software Foundation, Inc.
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
25#include <bits/atomic_futex.h>
26#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1)
27#if defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
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
37const unsigned futex_wait_op = 0;
38const unsigned futex_wake_op = 1;
39
40namespace std _GLIBCXX_VISIBILITY(default)
41{
42_GLIBCXX_BEGIN_NAMESPACE_VERSION
43
44  bool
45  __atomic_futex_unsigned_base::_M_futex_wait_until(unsigned *__addr,
46      unsigned __val,
47      bool __has_timeout, chrono::seconds __s, chrono::nanoseconds __ns)
48  {
49    if (!__has_timeout)
50      {
51	// Ignore whether we actually succeeded to block because at worst,
52	// we will fall back to spin-waiting.  The only thing we could do
53	// here on errors is abort.
54	int ret __attribute__((unused));
55	ret = syscall (SYS_futex, __addr, futex_wait_op, __val);
56	_GLIBCXX_DEBUG_ASSERT(ret == 0 || errno == EINTR || errno == EAGAIN);
57	return true;
58      }
59    else
60      {
61	struct timeval tv;
62	gettimeofday (&tv, NULL);
63	// Convert the absolute timeout value to a relative timeout
64	struct timespec rt;
65	rt.tv_sec = __s.count() - tv.tv_sec;
66	rt.tv_nsec = __ns.count() - tv.tv_usec * 1000;
67	if (rt.tv_nsec < 0)
68	  {
69	    rt.tv_nsec += 1000000000;
70	    --rt.tv_sec;
71	  }
72	// Did we already time out?
73	if (rt.tv_sec < 0)
74	  return false;
75
76	if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1)
77	  {
78	    _GLIBCXX_DEBUG_ASSERT(errno == EINTR || errno == EAGAIN
79				  || errno == ETIMEDOUT);
80	    if (errno == ETIMEDOUT)
81	      return false;
82	  }
83	return true;
84      }
85  }
86
87  void
88  __atomic_futex_unsigned_base::_M_futex_notify_all(unsigned* __addr)
89  {
90    // This syscall can fail for various reasons, including in situations
91    // in which there is no real error.  Thus, we don't bother checking
92    // the error codes.  See the futex documentation and glibc for background.
93    syscall (SYS_futex, __addr, futex_wake_op, INT_MAX);
94  }
95
96_GLIBCXX_END_NAMESPACE_VERSION
97}
98#endif
99#endif
100