1 // futex -*- C++ -*- 2 3 // Copyright (C) 2015-2018 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 37 const unsigned futex_wait_op = 0; 38 const unsigned futex_wake_op = 1; 39 40 namespace 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, nullptr); 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