1 // futex -*- C++ -*- 2 3 // Copyright (C) 2015-2020 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 #ifdef _GLIBCXX_HAS_GTHREADS 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 <ext/numeric_traits.h> 35 #include <debug/debug.h> 36 37 // Constants for the wait/wake futex syscall operations 38 const unsigned futex_wait_op = 0; 39 const unsigned futex_wake_op = 1; 40 41 namespace std _GLIBCXX_VISIBILITY(default) 42 { 43 _GLIBCXX_BEGIN_NAMESPACE_VERSION 44 45 using __gnu_cxx::__int_traits; 46 47 namespace 48 { 49 // Return the relative duration from (now_s + now_ns) to (abs_s + abs_ns) 50 // as a timespec. 51 struct timespec relative_timespec(chrono::seconds abs_s,chrono::nanoseconds abs_ns,time_t now_s,long now_ns)52 relative_timespec(chrono::seconds abs_s, chrono::nanoseconds abs_ns, 53 time_t now_s, long now_ns) 54 { 55 struct timespec rt; 56 57 // Did we already time out? 58 if (now_s > abs_s.count()) 59 { 60 rt.tv_sec = -1; 61 return rt; 62 } 63 64 const auto rel_s = abs_s.count() - now_s; 65 66 // Convert the absolute timeout to a relative timeout, without overflow. 67 if (rel_s > __int_traits<time_t>::__max) [[unlikely]] 68 { 69 rt.tv_sec = __int_traits<time_t>::__max; 70 rt.tv_nsec = 999999999; 71 } 72 else 73 { 74 rt.tv_sec = rel_s; 75 rt.tv_nsec = abs_ns.count() - now_ns; 76 if (rt.tv_nsec < 0) 77 { 78 rt.tv_nsec += 1000000000; 79 --rt.tv_sec; 80 } 81 } 82 83 return rt; 84 } 85 } // namespace 86 87 bool 88 __atomic_futex_unsigned_base:: _M_futex_wait_until(unsigned * __addr,unsigned __val,bool __has_timeout,chrono::seconds __s,chrono::nanoseconds __ns)89 _M_futex_wait_until(unsigned *__addr, unsigned __val, bool __has_timeout, 90 chrono::seconds __s, chrono::nanoseconds __ns) 91 { 92 if (!__has_timeout) 93 { 94 // Ignore whether we actually succeeded to block because at worst, 95 // we will fall back to spin-waiting. The only thing we could do 96 // here on errors is abort. 97 int ret __attribute__((unused)); 98 ret = syscall (SYS_futex, __addr, futex_wait_op, __val, nullptr); 99 __glibcxx_assert(ret == 0 || errno == EINTR || errno == EAGAIN); 100 return true; 101 } 102 else 103 { 104 struct timeval tv; 105 gettimeofday (&tv, NULL); 106 107 // Convert the absolute timeout value to a relative timeout 108 auto rt = relative_timespec(__s, __ns, tv.tv_sec, tv.tv_usec * 1000); 109 110 // Did we already time out? 111 if (rt.tv_sec < 0) 112 return false; 113 114 if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1) 115 { 116 __glibcxx_assert(errno == EINTR || errno == EAGAIN 117 || errno == ETIMEDOUT); 118 if (errno == ETIMEDOUT) 119 return false; 120 } 121 return true; 122 } 123 } 124 125 void _M_futex_notify_all(unsigned * __addr)126 __atomic_futex_unsigned_base::_M_futex_notify_all(unsigned* __addr) 127 { 128 // This syscall can fail for various reasons, including in situations 129 // in which there is no real error. Thus, we don't bother checking 130 // the error codes. See the futex documentation and glibc for background. 131 syscall (SYS_futex, __addr, futex_wake_op, INT_MAX); 132 } 133 134 _GLIBCXX_END_NAMESPACE_VERSION 135 } 136 #endif // defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1 137 #endif // _GLIBCXX_HAS_GTHREADS 138