libstdc++-v3/src/c++11/futex.cc

   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 #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 <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_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_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 // defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
  99 #endif // _GLIBCXX_HAS_GTHREADS