libstdc++-v3/src/c++11/futex.cc - gcc - Git at Google

 // futex -*- C++ -*-

 // Copyright (C) 2015-2021 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
 // terms of the GNU General Public License as published by the
 // Free Software Foundation; either version 3, or (at your option)
 // any later version.

 // This library is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 // GNU General Public License for more details.

 // Under Section 7 of GPL version 3, you are granted additional
 // permissions described in the GCC Runtime Library Exception, version
 // 3.1, as published by the Free Software Foundation.

 // You should have received a copy of the GNU General Public License and
 // a copy of the GCC Runtime Library Exception along with this program;
 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 // <http://www.gnu.org/licenses/>.

 #include <bits/atomic_futex.h>
 #ifdef _GLIBCXX_HAS_GTHREADS
 #if defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
 #include <chrono>
 #include <climits>
 #include <syscall.h>
 #include <unistd.h>
 #include <sys/time.h>
 #include <errno.h>
 #include <ext/numeric_traits.h>
 #include <debug/debug.h>

 #ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
 #include <unistd.h>
 #include <sys/syscall.h>
 #endif

 // Constants for the wait/wake futex syscall operations
 const unsigned futex_wait_op = 0;
 const unsigned futex_wait_bitset_op = 9;
 const unsigned futex_clock_monotonic_flag = 0;
 const unsigned futex_clock_realtime_flag = 256;
 const unsigned futex_bitset_match_any = ~0;
 const unsigned futex_wake_op = 1;

 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION

   using __gnu_cxx::__int_traits;

 namespace
 {
   std::atomic<bool> futex_clock_realtime_unavailable;
   std::atomic<bool> futex_clock_monotonic_unavailable;

 #if defined(SYS_futex_time64) && SYS_futex_time64 != SYS_futex
   // Userspace knows about the new time64 syscalls, so it's possible that
   // userspace has also updated timespec to use a 64-bit tv_sec.
   // The SYS_futex syscall still uses the old definition of timespec
   // where tv_sec is 32 bits, so define a type that matches that.
   struct syscall_timespec { long tv_sec; long tv_nsec; };
   using syscall_time_t = long;
 #else
   using syscall_timespec = ::timespec;
   using syscall_time_t = time_t;
 #endif

   // Return the relative duration from (now_s + now_ns) to (abs_s + abs_ns)
   // as a timespec suitable for syscalls.
   syscall_timespec
   relative_timespec(chrono::seconds abs_s, chrono::nanoseconds abs_ns,
 		    time_t now_s, long now_ns)
   {
     syscall_timespec rt;

     // Did we already time out?
     if (now_s > abs_s.count())
       {
 	rt.tv_sec = -1;
 	return rt;
       }

     const auto rel_s = abs_s.count() - now_s;

     // Convert the absolute timeout to a relative timeout, without overflow.
     if (rel_s > __int_traits<syscall_time_t>::__max) [[unlikely]]
       {
 	rt.tv_sec = __int_traits<syscall_time_t>::__max;
 	rt.tv_nsec = 999999999;
       }
     else
       {
 	rt.tv_sec = rel_s;
 	rt.tv_nsec = abs_ns.count() - now_ns;
 	if (rt.tv_nsec < 0)
 	  {
 	    rt.tv_nsec += 1000000000;
 	    --rt.tv_sec;
 	  }
       }

     return rt;
   }
 } // namespace

   bool
   __atomic_futex_unsigned_base::
   _M_futex_wait_until(unsigned *__addr, unsigned __val, bool __has_timeout,
 		      chrono::seconds __s, chrono::nanoseconds __ns)
   {
     if (!__has_timeout)
       {
 	// Ignore whether we actually succeeded to block because at worst,
 	// we will fall back to spin-waiting.  The only thing we could do
 	// here on errors is abort.
 	int ret __attribute__((unused));
 	ret = syscall (SYS_futex, __addr, futex_wait_op, __val, nullptr);
 	__glibcxx_assert(ret == 0 || errno == EINTR || errno == EAGAIN);
 	return true;
       }
     else
       {
 	if (!futex_clock_realtime_unavailable.load(std::memory_order_relaxed))
 	  {
 	    // futex sets errno=EINVAL for absolute timeouts before the epoch.
 	    if (__s.count() < 0)
 	      return false;

 	    syscall_timespec rt;
 	    if (__s.count() > __int_traits<syscall_time_t>::__max) [[unlikely]]
 	      rt.tv_sec = __int_traits<syscall_time_t>::__max;
 	    else
 	      rt.tv_sec = __s.count();
 	    rt.tv_nsec = __ns.count();

 	    if (syscall (SYS_futex, __addr,
 			 futex_wait_bitset_op | futex_clock_realtime_flag,
 			 __val, &rt, nullptr, futex_bitset_match_any) == -1)
 	      {
 		__glibcxx_assert(errno == EINTR || errno == EAGAIN
 				|| errno == ETIMEDOUT || errno == ENOSYS);
 		if (errno == ETIMEDOUT)
 		  return false;
 		if (errno == ENOSYS)
 		  {
 		    futex_clock_realtime_unavailable.store(true,
 						    std::memory_order_relaxed);
 		    // Fall through to legacy implementation if the system
 		    // call is unavailable.
 		  }
 		else
 		  return true;
 	      }
 	    else
 	      return true;
 	  }

 	// We only get to here if futex_clock_realtime_unavailable was
 	// true or has just been set to true.
 	struct timeval tv;
 	gettimeofday (&tv, NULL);

 	// Convert the absolute timeout value to a relative timeout
 	auto rt = relative_timespec(__s, __ns, tv.tv_sec, tv.tv_usec * 1000);

 	// Did we already time out?
 	if (rt.tv_sec < 0)
 	  return false;

 	if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1)
 	  {
 	    __glibcxx_assert(errno == EINTR || errno == EAGAIN
 			     || errno == ETIMEDOUT);
 	    if (errno == ETIMEDOUT)
 	      return false;
 	  }
 	return true;
       }
   }

   bool
   __atomic_futex_unsigned_base::
   _M_futex_wait_until_steady(unsigned *__addr, unsigned __val,
 			     bool __has_timeout,
 			     chrono::seconds __s, chrono::nanoseconds __ns)
   {
     if (!__has_timeout)
       {
 	// Ignore whether we actually succeeded to block because at worst,
 	// we will fall back to spin-waiting.  The only thing we could do
 	// here on errors is abort.
 	int ret __attribute__((unused));
 	ret = syscall (SYS_futex, __addr, futex_wait_op, __val, nullptr);
 	__glibcxx_assert(ret == 0 || errno == EINTR || errno == EAGAIN);
 	return true;
       }
     else
       {
 	if (!futex_clock_monotonic_unavailable.load(std::memory_order_relaxed))
 	  {
 	    // futex sets errno=EINVAL for absolute timeouts before the epoch.
 	    if (__s.count() < 0) [[unlikely]]
 	      return false;

 	    syscall_timespec rt;
 	    if (__s.count() > __int_traits<syscall_time_t>::__max) [[unlikely]]
 	      rt.tv_sec = __int_traits<syscall_time_t>::__max;
 	    else
 	      rt.tv_sec = __s.count();
 	    rt.tv_nsec = __ns.count();

 	    if (syscall (SYS_futex, __addr,
 			 futex_wait_bitset_op | futex_clock_monotonic_flag,
 			 __val, &rt, nullptr, futex_bitset_match_any) == -1)
 	      {
 		__glibcxx_assert(errno == EINTR || errno == EAGAIN
 				 || errno == ETIMEDOUT || errno == ENOSYS);
 		if (errno == ETIMEDOUT)
 		  return false;
 		else if (errno == ENOSYS)
 		  {
 		    futex_clock_monotonic_unavailable.store(true,
 						    std::memory_order_relaxed);
 		    // Fall through to legacy implementation if the system
 		    // call is unavailable.
 		  }
 		else
 		  return true;
 	      }
 	  }

 	// We only get to here if futex_clock_monotonic_unavailable was
 	// true or has just been set to true.
 	struct timespec ts;
 #ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
 	syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &ts);
 #else
 	clock_gettime(CLOCK_MONOTONIC, &ts);
 #endif

 	// Convert the absolute timeout value to a relative timeout
 	auto rt = relative_timespec(__s, __ns, ts.tv_sec, ts.tv_nsec);

 	// Did we already time out?
 	if (rt.tv_sec < 0)
 	  return false;

 	if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1)
 	  {
 	    __glibcxx_assert(errno == EINTR || errno == EAGAIN
 			     || errno == ETIMEDOUT);
 	    if (errno == ETIMEDOUT)
 	      return false;
 	  }
 	return true;
       }
   }

   void
   __atomic_futex_unsigned_base::_M_futex_notify_all(unsigned* __addr)
   {
     // This syscall can fail for various reasons, including in situations
     // in which there is no real error.  Thus, we don't bother checking
     // the error codes.  See the futex documentation and glibc for background.
     syscall (SYS_futex, __addr, futex_wake_op, INT_MAX);
   }

 _GLIBCXX_END_NAMESPACE_VERSION
 }
 #endif // defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
 #endif // _GLIBCXX_HAS_GTHREADS
	// futex -- C++ --

	// Copyright (C) 2015-2021 Free Software Foundation, Inc.
	//
	// This file is part of the GNU ISO C++ Library. This library is free
	// software; you can redistribute it and/or modify it under the
	// terms of the GNU General Public License as published by the
	// Free Software Foundation; either version 3, or (at your option)
	// any later version.

	// This library is distributed in the hope that it will be useful,
	// but WITHOUT ANY WARRANTY; without even the implied warranty of
	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	// GNU General Public License for more details.

	// Under Section 7 of GPL version 3, you are granted additional
	// permissions described in the GCC Runtime Library Exception, version
	// 3.1, as published by the Free Software Foundation.

	// You should have received a copy of the GNU General Public License and
	// a copy of the GCC Runtime Library Exception along with this program;
	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
	// <http://www.gnu.org/licenses/>.

	#include <bits/atomic_futex.h>
	#ifdef _GLIBCXX_HAS_GTHREADS
	#if defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
	#include <chrono>
	#include <climits>
	#include <syscall.h>
	#include <unistd.h>
	#include <sys/time.h>
	#include <errno.h>
	#include <ext/numeric_traits.h>
	#include <debug/debug.h>

	#ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
	#include <unistd.h>
	#include <sys/syscall.h>
	#endif

	// Constants for the wait/wake futex syscall operations
	const unsigned futex_wait_op = 0;
	const unsigned futex_wait_bitset_op = 9;
	const unsigned futex_clock_monotonic_flag = 0;
	const unsigned futex_clock_realtime_flag = 256;
	const unsigned futex_bitset_match_any = ~0;
	const unsigned futex_wake_op = 1;

	namespace std _GLIBCXX_VISIBILITY(default)
	{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION

	using __gnu_cxx::__int_traits;

	namespace
	{
	std::atomic<bool> futex_clock_realtime_unavailable;
	std::atomic<bool> futex_clock_monotonic_unavailable;

	#if defined(SYS_futex_time64) && SYS_futex_time64 != SYS_futex
	// Userspace knows about the new time64 syscalls, so it's possible that
	// userspace has also updated timespec to use a 64-bit tv_sec.
	// The SYS_futex syscall still uses the old definition of timespec
	// where tv_sec is 32 bits, so define a type that matches that.
	struct syscall_timespec { long tv_sec; long tv_nsec; };
	using syscall_time_t = long;
	#else
	using syscall_timespec = ::timespec;
	using syscall_time_t = time_t;
	#endif

	// Return the relative duration from (now_s + now_ns) to (abs_s + abs_ns)
	// as a timespec suitable for syscalls.
	syscall_timespec
	relative_timespec(chrono::seconds abs_s, chrono::nanoseconds abs_ns,
	time_t now_s, long now_ns)
	{
	syscall_timespec rt;

	// Did we already time out?
	if (now_s > abs_s.count())
	{
	rt.tv_sec = -1;
	return rt;
	}

	const auto rel_s = abs_s.count() - now_s;

	// Convert the absolute timeout to a relative timeout, without overflow.
	if (rel_s > __int_traits<syscall_time_t>::__max) [[unlikely]]
	{
	rt.tv_sec = __int_traits<syscall_time_t>::__max;
	rt.tv_nsec = 999999999;
	}
	else
	{
	rt.tv_sec = rel_s;
	rt.tv_nsec = abs_ns.count() - now_ns;
	if (rt.tv_nsec < 0)
	{
	rt.tv_nsec += 1000000000;
	--rt.tv_sec;
	}
	}

	return rt;
	}
	} // namespace

	bool
	__atomic_futex_unsigned_base::
	_M_futex_wait_until(unsigned *__addr, unsigned __val, bool __has_timeout,
	chrono::seconds __s, chrono::nanoseconds __ns)
	{
	if (!__has_timeout)
	{
	// Ignore whether we actually succeeded to block because at worst,
	// we will fall back to spin-waiting. The only thing we could do
	// here on errors is abort.
	int ret __attribute__((unused));
	ret = syscall (SYS_futex, __addr, futex_wait_op, __val, nullptr);
	__glibcxx_assert(ret == 0 \|\| errno == EINTR \|\| errno == EAGAIN);
	return true;
	}
	else
	{
	if (!futex_clock_realtime_unavailable.load(std::memory_order_relaxed))
	{
	// futex sets errno=EINVAL for absolute timeouts before the epoch.
	if (__s.count() < 0)
	return false;

	syscall_timespec rt;
	if (__s.count() > __int_traits<syscall_time_t>::__max) [[unlikely]]
	rt.tv_sec = __int_traits<syscall_time_t>::__max;
	else
	rt.tv_sec = __s.count();
	rt.tv_nsec = __ns.count();

	if (syscall (SYS_futex, __addr,
	futex_wait_bitset_op \| futex_clock_realtime_flag,
	__val, &rt, nullptr, futex_bitset_match_any) == -1)
	{
	__glibcxx_assert(errno == EINTR \|\| errno == EAGAIN
	\|\| errno == ETIMEDOUT \|\| errno == ENOSYS);
	if (errno == ETIMEDOUT)
	return false;
	if (errno == ENOSYS)
	{
	futex_clock_realtime_unavailable.store(true,
	std::memory_order_relaxed);
	// Fall through to legacy implementation if the system
	// call is unavailable.
	}
	else
	return true;
	}
	else
	return true;
	}

	// We only get to here if futex_clock_realtime_unavailable was
	// true or has just been set to true.
	struct timeval tv;
	gettimeofday (&tv, NULL);

	// Convert the absolute timeout value to a relative timeout
	auto rt = relative_timespec(__s, __ns, tv.tv_sec, tv.tv_usec * 1000);

	// Did we already time out?
	if (rt.tv_sec < 0)
	return false;

	if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1)
	{
	__glibcxx_assert(errno == EINTR \|\| errno == EAGAIN
	\|\| errno == ETIMEDOUT);
	if (errno == ETIMEDOUT)
	return false;
	}
	return true;
	}
	}

	bool
	__atomic_futex_unsigned_base::
	_M_futex_wait_until_steady(unsigned *__addr, unsigned __val,
	bool __has_timeout,
	chrono::seconds __s, chrono::nanoseconds __ns)
	{
	if (!__has_timeout)
	{
	// Ignore whether we actually succeeded to block because at worst,
	// we will fall back to spin-waiting. The only thing we could do
	// here on errors is abort.
	int ret __attribute__((unused));
	ret = syscall (SYS_futex, __addr, futex_wait_op, __val, nullptr);
	__glibcxx_assert(ret == 0 \|\| errno == EINTR \|\| errno == EAGAIN);
	return true;
	}
	else
	{
	if (!futex_clock_monotonic_unavailable.load(std::memory_order_relaxed))
	{
	// futex sets errno=EINVAL for absolute timeouts before the epoch.
	if (__s.count() < 0) [[unlikely]]
	return false;

	syscall_timespec rt;
	if (__s.count() > __int_traits<syscall_time_t>::__max) [[unlikely]]
	rt.tv_sec = __int_traits<syscall_time_t>::__max;
	else
	rt.tv_sec = __s.count();
	rt.tv_nsec = __ns.count();

	if (syscall (SYS_futex, __addr,
	futex_wait_bitset_op \| futex_clock_monotonic_flag,
	__val, &rt, nullptr, futex_bitset_match_any) == -1)
	{
	__glibcxx_assert(errno == EINTR \|\| errno == EAGAIN
	\|\| errno == ETIMEDOUT \|\| errno == ENOSYS);
	if (errno == ETIMEDOUT)
	return false;
	else if (errno == ENOSYS)
	{
	futex_clock_monotonic_unavailable.store(true,
	std::memory_order_relaxed);
	// Fall through to legacy implementation if the system
	// call is unavailable.
	}
	else
	return true;
	}
	}

	// We only get to here if futex_clock_monotonic_unavailable was
	// true or has just been set to true.
	struct timespec ts;
	#ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
	syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &ts);
	#else
	clock_gettime(CLOCK_MONOTONIC, &ts);
	#endif

	// Convert the absolute timeout value to a relative timeout
	auto rt = relative_timespec(__s, __ns, ts.tv_sec, ts.tv_nsec);

	// Did we already time out?
	if (rt.tv_sec < 0)
	return false;

	if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1)
	{
	__glibcxx_assert(errno == EINTR \|\| errno == EAGAIN
	\|\| errno == ETIMEDOUT);
	if (errno == ETIMEDOUT)
	return false;
	}
	return true;
	}
	}

	void
	__atomic_futex_unsigned_base::_M_futex_notify_all(unsigned* __addr)
	{
	// This syscall can fail for various reasons, including in situations
	// in which there is no real error. Thus, we don't bother checking
	// the error codes. See the futex documentation and glibc for background.
	syscall (SYS_futex, __addr, futex_wake_op, INT_MAX);
	}

	_GLIBCXX_END_NAMESPACE_VERSION
	}
	#endif // defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
	#endif // _GLIBCXX_HAS_GTHREADS