commit 4b07d1c0ab807fd0fbedacde1e9fec99a7d75b6d
Author: Torvald Riegel <triegel@redhat.com>
Date: Sun Nov 16 12:07:22 2014 +0100
libstdc++: Optimize synchronization in std::future if futexes are available.
* src/c++11/futex.cc: New file.
* include/bits/atomic_futex.h: New file.
* include/std/future (__future_base::_State_baseV2): Use
atomic_futex_unsigned instead of mutex+condvar.
* src/c++11/futex.cc: Likewise.
* include/Makefile.am: Add atomic_futex.h.
* include/Makefile.in: Likewise.
* src/c++11/Makefile.am: Add futex.cc.
* src/c++11/Makefile.in: Likewise.
@@ -1759,6 +1759,11 @@ GLIBCXX_3.4.21 {
_ZNKSt8time_getI[cw]St19istreambuf_iteratorI[cw]St11char_traitsI[cw]EEE3getES3_S3_RSt8ios_baseRSt12_Ios_IostateP2tmPK[cw]SC_;
_ZNKSt8time_getI[cw]St19istreambuf_iteratorI[cw]St11char_traitsI[cw]EEE6do_getES3_S3_RSt8ios_baseRSt12_Ios_IostateP2tmcc;
+ extern "C++"
+ {
+ std::__atomic_futex_unsigned_base*;
+ };
+
} GLIBCXX_3.4.20;
@@ -83,6 +83,7 @@ bits_headers = \
${bits_srcdir}/allocated_ptr.h \
${bits_srcdir}/allocator.h \
${bits_srcdir}/atomic_base.h \
+ ${bits_srcdir}/atomic_futex.h \
${bits_srcdir}/basic_ios.h \
${bits_srcdir}/basic_ios.tcc \
${bits_srcdir}/basic_string.h \
@@ -351,6 +351,7 @@ bits_headers = \
${bits_srcdir}/allocated_ptr.h \
${bits_srcdir}/allocator.h \
${bits_srcdir}/atomic_base.h \
+ ${bits_srcdir}/atomic_futex.h \
${bits_srcdir}/basic_ios.h \
${bits_srcdir}/basic_ios.tcc \
${bits_srcdir}/basic_string.h \
new file mode 100644
@@ -0,0 +1,288 @@
+// -*- C++ -*- header.
+
+// Copyright (C) 2015 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/>.
+
+/** @file bits/atomic_futex.h
+ * This is an internal header file, included by other library headers.
+ * Do not attempt to use it directly.
+ */
+
+#ifndef _GLIBCXX_ATOMIC_FUTEX_H
+#define _GLIBCXX_ATOMIC_FUTEX_H 1
+
+#pragma GCC system_header
+
+#include <bits/c++config.h>
+#include <atomic>
+#include <chrono>
+#if !defined(_GLIBCXX_HAVE_LINUX_FUTEX)
+#include <mutex>
+#include <condition_variable>
+#endif
+
+#ifndef _GLIBCXX_ALWAYS_INLINE
+#define _GLIBCXX_ALWAYS_INLINE inline __attribute__((always_inline))
+#endif
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+#if defined(_GLIBCXX_HAVE_LINUX_FUTEX)
+ struct __atomic_futex_unsigned_base
+ {
+ // Returns false iff a timeout occurred.
+ bool
+ _M_futex_wait_until(unsigned *__addr, unsigned __val, bool __has_timeout,
+ chrono::seconds __s, chrono::nanoseconds __ns);
+
+ // This can be executed after the object has been destroyed.
+ static void _M_futex_notify_all(unsigned* __addr);
+ };
+
+ template <unsigned _Waiter_bit = 0x80000000>
+ struct __atomic_futex_unsigned : __atomic_futex_unsigned_base
+ {
+ typedef chrono::system_clock __clock_t;
+
+ // XXX We expect this to be lock-free, and having the payload at offset 0.
+#if ATOMIC_INT_LOCK_FREE < 2
+# error We require lock-free atomic operations on int
+#endif
+ atomic<unsigned> _M_data;
+
+ __atomic_futex_unsigned(unsigned __data) : _M_data(__data)
+ { }
+
+ _GLIBCXX_ALWAYS_INLINE unsigned
+ _M_load(memory_order __mo)
+ {
+ return _M_data.load(__mo) & ~_Waiter_bit;
+ }
+
+ private:
+
+ // If a timeout occurs, returns a current value after the timeout;
+ // otherwise, returns the operand's value if equal is true or a different
+ // value if equal is false.
+ // The assumed value is the caller's assumption about the current value
+ // when making the call.
+ unsigned
+ _M_load_and_test_until(unsigned __assumed, unsigned __operand,
+ bool __equal, memory_order __mo, bool __has_timeout,
+ chrono::seconds __s, chrono::nanoseconds __ns)
+ {
+ for (;;)
+ {
+ // Don't bother checking the value again because we expect the caller to
+ // have done it recently.
+ // memory_order_relaxed is sufficient because we can rely on just the
+ // modification order (store_notify uses an atomic RMW operation too),
+ // and the futex syscalls synchronize between themselves.
+ _M_data.fetch_or(_Waiter_bit, memory_order_relaxed);
+ bool __ret;
+ __ret = _M_futex_wait_until((unsigned*)(void*)&_M_data,
+ __assumed | _Waiter_bit, __has_timeout, __s, __ns);
+ // Fetch the current value after waiting (clears _Waiter_bit).
+ __assumed = _M_load(__mo);
+ if (!__ret || ((__operand == __assumed) == __equal))
+ return __assumed;
+ // TODO adapt wait time
+ }
+ }
+
+ // Returns the operand's value if equal is true or a different value if
+ // equal is false.
+ // The assumed value is the caller's assumption about the current value
+ // when making the call.
+ unsigned
+ _M_load_and_test(unsigned __assumed, unsigned __operand,
+ bool __equal, memory_order __mo)
+ {
+ return _M_load_and_test_until(__assumed, __operand, __equal, __mo,
+ false, chrono::seconds(0), chrono::nanoseconds(0));
+ }
+
+ // If a timeout occurs, returns a current value after the timeout;
+ // otherwise, returns the operand's value if equal is true or a different
+ // value if equal is false.
+ // The assumed value is the caller's assumption about the current value
+ // when making the call.
+ template<typename _Dur>
+ unsigned
+ _M_load_and_test_until_impl(unsigned __assumed, unsigned __operand,
+ bool __equal, memory_order __mo,
+ const chrono::time_point<__clock_t, _Dur>& __atime)
+ {
+ auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
+ auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
+ // XXX correct?
+ return _M_load_and_test_until(__assumed, __operand, __equal, __mo,
+ true, __s.time_since_epoch(), __ns);
+ }
+
+ public:
+
+ _GLIBCXX_ALWAYS_INLINE unsigned
+ _M_load_when_not_equal(unsigned __val, memory_order __mo)
+ {
+ unsigned __i = _M_load(__mo);
+ if ((__i & ~_Waiter_bit) != __val) return;
+ // TODO Spin-wait first.
+ return _M_load_and_test(__i, __val, false, __mo);
+ }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ _M_load_when_equal(unsigned __val, memory_order __mo)
+ {
+ unsigned __i = _M_load(__mo);
+ if ((__i & ~_Waiter_bit) == __val)
+ return;
+ // TODO Spin-wait first.
+ _M_load_and_test(__i, __val, true, __mo);
+ }
+
+ // Returns false iff a timeout occurred.
+ template<typename _Rep, typename _Period>
+ _GLIBCXX_ALWAYS_INLINE bool
+ _M_load_when_equal_for(unsigned __val, memory_order __mo,
+ const chrono::duration<_Rep, _Period>& __rtime)
+ {
+ return _M_load_when_equal_until(__val, __mo, __clock_t::now() + __rtime);
+ }
+
+ // Returns false iff a timeout occurred.
+ template<typename _Clock, typename _Duration>
+ _GLIBCXX_ALWAYS_INLINE bool
+ _M_load_when_equal_until(unsigned __val, memory_order __mo,
+ const chrono::time_point<_Clock, _Duration>& __atime)
+ {
+ // DR 887 - Sync unknown clock to known clock.
+ const typename _Clock::time_point __c_entry = _Clock::now();
+ const __clock_t::time_point __s_entry = __clock_t::now();
+ const auto __delta = __atime - __c_entry;
+ const auto __s_atime = __s_entry + __delta;
+ return _M_load_when_equal_until(__val, __mo, __s_atime);
+ }
+
+ // Returns false iff a timeout occurred.
+ template<typename _Duration>
+ _GLIBCXX_ALWAYS_INLINE bool
+ _M_load_when_equal_until(unsigned __val, memory_order __mo,
+ const chrono::time_point<__clock_t, _Duration>& __atime)
+ {
+ unsigned __i = _M_load(__mo);
+ if ((__i & ~_Waiter_bit) == __val)
+ return true;
+ // TODO Spin-wait first. Ignore effect on timeout.
+ __i = _M_load_and_test_until_impl(__i, __val, true, __mo, __atime);
+ return (__i & ~_Waiter_bit) == __val;
+ }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ _M_store_notify_all(unsigned __val, memory_order __mo)
+ {
+ unsigned* __futex = (unsigned *)(void *)&_M_data;
+ if (_M_data.exchange(__val, __mo) & _Waiter_bit)
+ _M_futex_notify_all(__futex);
+ }
+
+ };
+
+#else
+
+ // If futexes are not available, use a mutex and a condvar to wait.
+ // Because we access the data only within critical sections, all accesses
+ // are sequentially consistent; thus, we satisfy any provided memory_order.
+ template <unsigned _Waiter_bit = 0x80000000>
+ struct __atomic_futex_unsigned
+ {
+ typedef chrono::system_clock __clock_t;
+
+ unsigned _M_data;
+ mutex _M_mutex;
+ condition_variable _M_condvar;
+
+ __atomic_futex_unsigned(unsigned __data) : _M_data(__data)
+ { }
+
+ _GLIBCXX_ALWAYS_INLINE unsigned
+ _M_load(memory_order __mo)
+ {
+ unique_lock<mutex> __lock(_M_mutex);
+ return _M_data;
+ }
+
+ _GLIBCXX_ALWAYS_INLINE unsigned
+ _M_load_when_not_equal(unsigned __val, memory_order __mo)
+ {
+ unique_lock<mutex> __lock(_M_mutex);
+ while (_M_data == __val)
+ _M_condvar.wait(__lock);
+ return _M_data;
+ }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ _M_load_when_equal(unsigned __val, memory_order __mo)
+ {
+ unique_lock<mutex> __lock(_M_mutex);
+ while (_M_data != __val)
+ _M_condvar.wait(__lock);
+ }
+
+ template<typename _Rep, typename _Period>
+ _GLIBCXX_ALWAYS_INLINE bool
+ _M_load_when_equal_for(unsigned __val, memory_order __mo,
+ const chrono::duration<_Rep, _Period>& __rtime)
+ {
+ unique_lock<mutex> __lock(_M_mutex);
+ return _M_condvar.wait_for(__lock, __rtime,
+ [&] { return _M_data == __val;});
+ }
+
+ template<typename _Clock, typename _Duration>
+ _GLIBCXX_ALWAYS_INLINE bool
+ _M_load_when_equal_until(unsigned __val, memory_order __mo,
+ const chrono::time_point<_Clock, _Duration>& __atime)
+ {
+ unique_lock<mutex> __lock(_M_mutex);
+ return _M_condvar.wait_until(__lock, __atime,
+ [&] { return _M_data == __val;});
+ }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ _M_store_notify_all(unsigned __val, memory_order __mo)
+ {
+ unique_lock<mutex> __lock(_M_mutex);
+ _M_data = __val;
+ _M_condvar.notify_all();
+ }
+
+ };
+
+#endif
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+
+#endif
@@ -41,6 +41,7 @@
#include <condition_variable>
#include <system_error>
#include <atomic>
+#include <bits/atomic_futex.h>
#include <bits/functexcept.h>
#include <bits/unique_ptr.h>
#include <bits/shared_ptr.h>
@@ -294,15 +295,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
typedef _Ptr<_Result_base> _Ptr_type;
+ enum _Status : unsigned {
+ __not_ready,
+ __ready
+ };
+
_Ptr_type _M_result;
- mutex _M_mutex;
- condition_variable _M_cond;
- atomic_flag _M_retrieved = ATOMIC_FLAG_INIT;
- bool _M_ready = false;
+ __atomic_futex_unsigned<> _M_status;
+ atomic_flag _M_retrieved = ATOMIC_FLAG_INIT;
once_flag _M_once;
public:
- _State_baseV2() noexcept = default;
+ _State_baseV2() noexcept : _M_result(), _M_status(_Status::__not_ready)
+ { }
_State_baseV2(const _State_baseV2&) = delete;
_State_baseV2& operator=(const _State_baseV2&) = delete;
virtual ~_State_baseV2() = default;
@@ -312,9 +317,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
// Run any deferred function or join any asynchronous thread:
_M_complete_async();
-
- unique_lock<mutex> __lock(_M_mutex);
- _M_cond.wait(__lock, [&] { return _M_ready; });
+ // Acquire MO makes sure this synchronizes with the thread that made
+ // the future ready.
+ _M_status._M_load_when_equal(_Status::__ready, memory_order_acquire);
return *_M_result;
}
@@ -322,12 +327,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
future_status
wait_for(const chrono::duration<_Rep, _Period>& __rel)
{
- unique_lock<mutex> __lock(_M_mutex);
- if (_M_ready)
+ // First, check if the future has been made ready. Use acquire MO
+ // to synchronize with the thread that made it ready.
+ if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
return future_status::ready;
- if (_M_has_deferred())
+ if (_M_is_deferred_future())
return future_status::deferred;
- if (_M_cond.wait_for(__lock, __rel, [&] { return _M_ready; }))
+ if (_M_status._M_load_when_equal_for(_Status::__ready,
+ memory_order_acquire, __rel))
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2100. timed waiting functions must also join
@@ -349,12 +356,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
future_status
wait_until(const chrono::time_point<_Clock, _Duration>& __abs)
{
- unique_lock<mutex> __lock(_M_mutex);
- if (_M_ready)
+ // First, check if the future has been made ready. Use acquire MO
+ // to synchronize with the thread that made it ready.
+ if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
return future_status::ready;
- if (_M_has_deferred())
+ if (_M_is_deferred_future())
return future_status::deferred;
- if (_M_cond.wait_until(__lock, __abs, [&] { return _M_ready; }))
+ if (_M_status._M_load_when_equal_until(_Status::__ready,
+ memory_order_acquire, __abs))
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2100. timed waiting functions must also join
@@ -367,45 +376,37 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
// Provide a result to the shared state and make it ready.
- // Atomically performs:
- // if (!_M_ready) {
- // _M_result = __res();
- // _M_ready = true;
- // }
+ // Calls at most once: _M_result = __res();
void
_M_set_result(function<_Ptr_type()> __res, bool __ignore_failure = false)
{
- unique_lock<mutex> __lock(_M_mutex, defer_lock);
+ bool __did_set = false;
// all calls to this function are serialized,
// side-effects of invoking __res only happen once
call_once(_M_once, &_State_baseV2::_M_do_set, this,
- std::__addressof(__res), std::__addressof(__lock));
- if (__lock.owns_lock())
- {
- _M_ready = true;
- _M_cond.notify_all();
- }
+ std::__addressof(__res), std::__addressof(__did_set));
+ if (__did_set)
+ // Use release MO to synchronize with observers of the ready state.
+ _M_status._M_store_notify_all(_Status::__ready,
+ memory_order_release);
else if (!__ignore_failure)
__throw_future_error(int(future_errc::promise_already_satisfied));
}
// Provide a result to the shared state but delay making it ready
// until the calling thread exits.
- // Atomically performs:
- // if (!_M_ready) {
- // _M_result = __res();
- // }
+ // Calls at most once: _M_result = __res();
void
_M_set_delayed_result(function<_Ptr_type()> __res,
weak_ptr<_State_baseV2> __self)
{
+ bool __did_set = false;
unique_ptr<_Make_ready> __mr{new _Make_ready};
- unique_lock<mutex> __lock(_M_mutex, defer_lock);
// all calls to this function are serialized,
// side-effects of invoking __res only happen once
call_once(_M_once, &_State_baseV2::_M_do_set, this,
- std::__addressof(__res), std::__addressof(__lock));
- if (!__lock.owns_lock())
+ std::__addressof(__res), std::__addressof(__did_set));
+ if (!__did_set)
__throw_future_error(int(future_errc::promise_already_satisfied));
__mr->_M_shared_state = std::move(__self);
__mr->_M_set();
@@ -424,12 +425,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// provider is abandoning this shared state, so noone can be
// trying to make the shared state ready at the same time, and
// we can access _M_result directly instead of through call_once.
- {
- lock_guard<mutex> __lock(_M_mutex);
- _M_result.swap(__res);
- _M_ready = true;
- }
- _M_cond.notify_all();
+ _M_result.swap(__res);
+ // Use release MO to synchronize with observers of the ready state.
+ _M_status._M_store_notify_all(_Status::__ready,
+ memory_order_release);
}
}
@@ -523,18 +522,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
private:
// The function invoked with std::call_once(_M_once, ...).
void
- _M_do_set(function<_Ptr_type()>* __f, unique_lock<mutex>* __lock)
+ _M_do_set(function<_Ptr_type()>* __f, bool* __did_set)
{
- _Ptr_type __res = (*__f)(); // do not hold lock while running setter
- __lock->lock();
- _M_result.swap(__res);
+ _Ptr_type __res = (*__f)();
+ // Notify the caller that we did try to set; if we do not throw an
+ // exception, the caller will be aware that it did set (e.g., see
+ // _M_set_result).
+ *__did_set = true;
+ _M_result.swap(__res); // nothrow
}
// Wait for completion of async function.
virtual void _M_complete_async() { }
// Return true if state corresponds to a deferred function.
- virtual bool _M_has_deferred() const { return false; }
+ virtual bool _M_is_deferred_future() const { return false; }
struct _Make_ready final : __at_thread_exit_elt
{
@@ -1606,7 +1608,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Caller should check whether the state is ready first, because this
// function will return true even after the deferred function has run.
- virtual bool _M_has_deferred() const { return true; }
+ virtual bool _M_is_deferred_future() const { return true; }
};
// Common functionality hoisted out of the _Async_state_impl template.
@@ -59,6 +59,7 @@ sources = \
debug.cc \
functexcept.cc \
functional.cc \
+ futex.cc \
future.cc \
hash_c++0x.cc \
hashtable_c++0x.cc \
@@ -73,7 +73,7 @@ libc__11convenience_la_LIBADD =
@ENABLE_DUAL_ABI_TRUE@ cxx11-shim_facets.lo cxx11-stdexcept.lo
am__objects_2 = ctype_configure_char.lo ctype_members.lo
am__objects_3 = chrono.lo condition_variable.lo cow-stdexcept.lo \
- ctype.lo debug.lo functexcept.lo functional.lo future.lo \
+ ctype.lo debug.lo functexcept.lo functional.lo futex.lo future.lo \
hash_c++0x.lo hashtable_c++0x.lo ios.lo limits.lo mutex.lo \
placeholders.lo random.lo regex.lo shared_ptr.lo \
snprintf_lite.lo system_error.lo thread.lo $(am__objects_1) \
@@ -350,6 +350,7 @@ sources = \
debug.cc \
functexcept.cc \
functional.cc \
+ futex.cc \
future.cc \
hash_c++0x.cc \
hashtable_c++0x.cc \
new file mode 100644
@@ -0,0 +1,97 @@
+// futex -*- C++ -*-
+
+// Copyright (C) 2015 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/c++config.h>
+#if defined(_GLIBCXX_HAVE_LINUX_FUTEX)
+#include <bits/atomic_futex.h>
+#include <chrono>
+#include <climits>
+#include <syscall.h>
+#include <unistd.h>
+#include <sys/time.h>
+#include <errno.h>
+#include <debug/debug.h>
+
+// Constants for the wait/wake futex syscall operations
+const unsigned futex_wait_op = 0;
+const unsigned futex_wake_op = 1;
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+ 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);
+ _GLIBCXX_DEBUG_ASSERT(ret == 0 || errno == EINTR || errno == EAGAIN);
+ return true;
+ }
+ else
+ {
+ struct timeval tv;
+ gettimeofday (&tv, NULL);
+ // Convert the absolute timeout value to a relative timeout
+ struct timespec rt;
+ rt.tv_sec = __s.count() - tv.tv_sec;
+ rt.tv_nsec = __ns.count() - tv.tv_usec * 1000;
+ if (rt.tv_nsec < 0)
+ {
+ rt.tv_nsec += 1000000000;
+ --rt.tv_sec;
+ }
+ // Did we already time out?
+ if (rt.tv_sec < 0)
+ return false;
+
+ if (syscall (SYS_futex, __addr, futex_wait_op, __val, &rt) == -1)
+ {
+ _GLIBCXX_DEBUG_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);
+ }
+
+}
+#endif
@@ -89,11 +89,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
unique_ptr<_Make_ready> mr{static_cast<_Make_ready*>(p)};
if (auto state = mr->_M_shared_state.lock())
{
- {
- lock_guard<mutex> __lock{state->_M_mutex};
- state->_M_ready = true;
- }
- state->_M_cond.notify_all();
+ // Use release MO to synchronize with observers of the ready state.
+ state->_M_status._M_store_notify_all(_Status::__ready,
+ memory_order_release);
}
}