On 05/06/20 17:29 -0700, Thomas Rodgers wrote:
Add support for -
atomic wait/notify_one/notify_all
counting_semaphore
binary_semaphore
latch
* include/Makefile.am (bits_headers): Add new header.
* include/Makefile.in: Regenerate.
* include/bits/atomic_base.h (__atomic_base<_Itp>::wait): Define.
(__atomic_base<_Itp>::notify_one): Likewise.
(__atomic_base<_Itp>::notify_all): Likewise.
(__atomic_base<_Ptp*>::wait): Likewise.
(__atomic_base<_Ptp*>::notify_one): Likewise.
(__atomic_base<_Ptp*>::notify_all): Likewise.
(__atomic_impl::wait): Likewise.
(__atomic_impl::notify_one): Likewise.
(__atomic_impl::notify_all): Likewise.
(__atomic_float<_Fp>::wait): Likewise.
(__atomic_float<_Fp>::notify_one): Likewise.
(__atomic_float<_Fp>::notify_all): Likewise.
(__atomic_ref<_Tp>::wait): Likewise.
(__atomic_ref<_Tp>::notify_one): Likewise.
(__atomic_ref<_Tp>::notify_all): Likewise.
(atomic_wait<_Tp>): Likewise.
(atomic_wait_explicit<_Tp>): Likewise.
(atomic_notify_one<_Tp>): Likewise.
(atomic_notify_all<_Tp>): Likewise.
* include/bits/atomic_wait.h: New file.
* include/bits/atomic_timed_wait.h: New file.
* include/bits/semaphore_base.h: New file.
* include/std/atomic (atomic<bool>::wait): Define.
(atomic<bool>::wait_one): Likewise.
(atomic<bool>::wait_all): Likewise.
(atomic<_Tp>::wait): Likewise.
(atomic<_Tp>::wait_one): Likewise.
(atomic<_Tp>::wait_all): Likewise.
(atomic<_Tp*>::wait): Likewise.
(atomic<_Tp*>::wait_one): Likewise.
(atomic<_Tp*>::wait_all): Likewise.
* include/std/latch: New file.
* include/std/semaphore: New file.
* include/std/version: Add __cpp_lib_semaphore and
__cpp_lib_latch defines.
* testsuite/29_atomic/atomic/wait_notify/atomic_refs.cc: New test.
* testsuite/29_atomic/atomic/wait_notify/bool.cc: Likewise.
* testsuite/29_atomic/atomic/wait_notify/integrals.cc: Likewise.
* testsuite/29_atomic/atomic/wait_notify/floats.cc: Likewise.
* testsuite/29_atomic/atomic/wait_notify/pointers.cc: Likewise.
* testsuite/29_atomic/atomic/wait_notify/generic.h: New File.
* testsuite/30_thread/semaphore/1.cc: New test.
* testsuite/30_thread/semaphore/2.cc: Likewise.
* testsuite/30_thread/semaphore/least_max_value_neg.cc: Likewise.
* testsuite/30_thread/semaphore/try_acquire.cc: Likewise.
* testsuite/30_thread/semaphore/try_acquire_for.cc: Likewise.
* testsuite/30_thread/semaphore/try_acquire_futex.cc: Likewise.
* testsuite/30_thread/semaphore/try_acquire_posix.cc: Likewise.
* testsuite/30_thread/semaphore/try_acquire_until.cc: Likewise.
* testsuite/30_thread/latch/1.cc: New test.
* testsuite/30_thread/latch/2.cc: New test.
* testsuite/30_thread/latch/3.cc: New test.
diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index 80aeb3f8959..b3ac1a3365f 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -52,6 +52,7 @@ std_headers = \
${std_srcdir}/iostream \
${std_srcdir}/istream \
${std_srcdir}/iterator \
+ ${std_srcdir}/latch\
Missing space before the backslash here.
${std_srcdir}/limits \
${std_srcdir}/list \
${std_srcdir}/locale \
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -823,6 +851,30 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
int(__m1), int(__m2));
}
+#if __cplusplus > 201703L
+ _GLIBCXX_ALWAYS_INLINE void
+ wait(__pointer_type __old, memory_order __m = memory_order_seq_cst)
noexcept
This line should be < 80 cols.
+ {
@@ -911,6 +963,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
int(__success), int(__failure));
}
+#if __cplusplus > 201703L
+ template<typename _Tp>
+ _GLIBCXX_ALWAYS_INLINE void
+ wait(const _Tp* __ptr, _Val<_Tp> __old, memory_order __m =
memory_order_seq_cst) noexcept
And this one.
@@ -1164,6 +1242,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__cmpexch_failure_order(__order));
}
+ _GLIBCXX_ALWAYS_INLINE void
+ wait(_Fp __old, memory_order __m = memory_order_seq_cst) const noexcept
+ { __atomic_impl::wait(&_M_fp, __old, __m); }
+
+ // TODO add const volatile overload
+
+ _GLIBCXX_ALWAYS_INLINE void
+ notify_one() const noexcept
+ { __atomic_impl::notify_one(&_M_fp); }
+
+ // TODO add const volatile overload
+
+ _GLIBCXX_ALWAYS_INLINE void
+ notify_all() const noexcept
+ { __atomic_impl::notify_all(&_M_fp); }
+
+ // TODO add const volatile overload
Please add a newline after this comment.
value_type
fetch_add(value_type __i,
memory_order __m = memory_order_seq_cst) noexcept
@@ -1301,6 +1396,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__cmpexch_failure_order(__order));
}
+ _GLIBCXX_ALWAYS_INLINE void
+ wait(_Tp __old, memory_order __m = memory_order_seq_cst) const noexcept
+ { __atomic_impl::wait(_M_ptr, __old, __m); }
+
+ // TODO add const volatile overload
+
+ _GLIBCXX_ALWAYS_INLINE void
+ notify_one() const noexcept
+ { __atomic_impl::notify_one(_M_ptr); }
+
+ // TODO add const volatile overload
+
+ _GLIBCXX_ALWAYS_INLINE void
+ notify_all() const noexcept
+ { __atomic_impl::notify_all(_M_ptr); }
+
The TODO comment seems to be missing here, and after some notify_all
cases below. Please either add one after every non-volatile function
that's missing a volatile overload, or just put one "TODO volatile
overloads of wait and notify_{one,all}" comment in each class.
diff --git a/libstdc++-v3/include/bits/atomic_timed_wait.h
b/libstdc++-v3/include/bits/atomic_timed_wait.h
new file mode 100644
index 00000000000..adef80aca61
--- /dev/null
+++ b/libstdc++-v3/include/bits/atomic_timed_wait.h
@@ -0,0 +1,282 @@
+// -*- C++ -*- header.
+
+// Copyright (C) 2020 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_timed_wait.h
+ * This is an internal header file, included by other library headers.
+ * Do not attempt to use it directly. @headername{atomic}
+ */
+
+#ifndef _GLIBCXX_ATOMIC_TIMED_WAIT_H
+#define _GLIBCXX_ATOMIC_TIMED_WAIT_H 1
+
+#pragma GCC system_header
+
+#include <bits/c++config.h>
+#include <bits/functional_hash.h>
+#include <bits/atomic_wait.h>
+
+#include <chrono>
+
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+#include <sys/time.h>
+#endif
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+ _GLIBCXX_BEGIN_NAMESPACE_VERSION
No indentation for these BEGIN/END macros.
+
+ enum class __atomic_wait_status { __no_timeout, __timeout };
It seems a shame to have yet another status macro when we already have
cv_status and future_status which define enumerators with the same
names, but I suppose it's a bit confusing to reuse them. Maybe you
could just do:
using __atomic_wait_status = cv_status;
and then refer to __atomic_wait_status::no_timeout and
__atomic_wait_status::timeout, what do you think?
Even if it's a new distinct enum type, you could use no_timeout and
timeout as the enumerator names, because those are reserved names
anyway.
+ namespace __detail
+ {
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+ enum
I think unnamed enum types in headers cause problems for modules.
+ {
+ __futex_wait_bitset_private = __futex_wait_bitset | __futex_private_flag,
+ __futex_wake_bitset_private = __futex_wake_bitset | __futex_private_flag,
+ __futex_bitset_match_any = 0xffffffff
+ };
+
+ using __platform_wait_clock_t = chrono::steady_clock;
+
+ template<typename _Duration>
+ __atomic_wait_status
+ __platform_wait_until_impl(__platform_wait_t* __addr, __platform_wait_t
__val,
+ const chrono::time_point<__platform_wait_clock_t,
_Duration>& __atime) noexcept
+ {
+ auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
+ auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
+
+ struct timespec __rt =
+ {
+ static_cast<std::time_t>(__s.time_since_epoch().count()),
+ static_cast<long>(__ns.count())
+ };
+
+ auto __e = syscall (SYS_futex, __addr, __futex_wait_bitset_private, __val,
&__rt,
+ nullptr, __futex_bitset_match_any);
+ if (__e && !(errno == EINTR || errno == EAGAIN || errno == ETIMEDOUT))
+ std::terminate();
+ return (__platform_wait_clock_t::now() < __atime)
+ ? __atomic_wait_status::__no_timeout :
__atomic_wait_status::__timeout;
+ }
+
+ template<typename _Clock, typename _Duration>
+ __atomic_wait_status
+ __platform_wait_until(__platform_wait_t* __addr, __platform_wait_t __val,
+ const chrono::time_point<_Clock, _Duration>&
__atime)
+ {
+ if constexpr (std::is_same_v<__platform_wait_clock_t, _Clock>)
+ {
+ return __platform_wait_until_impl(__addr, __val, __atime);
Since this is calling a free function with arguments of
program-defined types (the clock and duration), it needs to be
qualified (whereas the is_same_v above doesn't need to be qualified,
although that's harmless).
+ }
+ else
+ {
+ const typename _Clock::time_point __c_entry = _Clock::now();
+ const __platform_wait_clock_t::time_point __s_entry =
+ __platform_wait_clock_t::now();
+ const auto __delta = __atime - __c_entry;
+ const auto __s_atime = __s_entry + __delta;
+ if (__platform_wait_until_impl(__addr, __val, __s_atime) ==
__atomic_wait_status::__no_timeout)
+ return __atomic_wait_status::__no_timeout;
+
+ // We got a timeout when measured against __clock_t but
+ // we need to check against the caller-supplied clock
+ // to tell whether we should return a timeout.
+ if (_Clock::now() < __atime)
+ return __atomic_wait_status::__no_timeout;
+ return __atomic_wait_status::__timeout;
+ }
+ }
+#endif
+
+#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
+ template<typename _Duration>
+ __atomic_wait_status
+ __cond_wait_until_impl(__gthread_cond_t* __cv,
+ unique_lock<mutex>& __lock,
+ const chrono::time_point<chrono::steady_clock, _Duration>& __atime)
+ {
+ auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
+ auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
+
+ __gthread_time_t __ts =
+ {
+ static_cast<std::time_t>(__s.time_since_epoch().count()),
+ static_cast<long>(__ns.count())
+ };
+
+ pthread_cond_clockwait(__cv, __lock.mutex()->native_handle(),
+ CLOCK_MONOTONIC,
+ &__ts);
+ return (chrono::steady_clock::now() < __atime)
+ ? __atomic_wait_status::__no_timeout :
__atomic_wait_status::__timeout;
+ }
+#endif
+
+ template<typename _Duration>
+ __atomic_wait_status
+ __cond_wait_until_impl(__gthread_cond_t* __cv,
+ unique_lock<std::mutex>& __lock,
+ const chrono::time_point<chrono::system_clock, _Duration>& __atime)
+ {
+ auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
+ auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
+
+ __gthread_time_t __ts =
+ {
+ static_cast<std::time_t>(__s.time_since_epoch().count()),
+ static_cast<long>(__ns.count())
+ };
+
+ __gthread_cond_timedwait(__cv, __lock.mutex()->native_handle(),
+ &__ts);
+ return (chrono::system_clock::now() < __atime)
+ ? __atomic_wait_status::__no_timeout
+ : __atomic_wait_status::__timeout;
+ }
+
+ // return true if timeout
+ template<typename _Clock, typename _Duration>
+ __atomic_wait_status
+ __cond_wait_until(__gthread_cond_t* __cv,
+ unique_lock<std::mutex>& __lock,
+ const chrono::time_point<_Clock, _Duration>& __atime)
+ {
+#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
+ using __clock_t = chrono::steady_clock;
+#else
+ using __clock_t = chrono::system_clock;
+#endif
+ 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;
+ if (__cond_wait_until_impl(__cv, __lock, __s_atime))
__cond_wait_until_impl should be qualified.
+ return __atomic_wait_status::__no_timeout;
+ // We got a timeout when measured against __clock_t but
+ // we need to check against the caller-supplied clock
+ // to tell whether we should return a timeout.
+ if (_Clock::now() < __atime)
+ return __atomic_wait_status::__no_timeout;
+ return __atomic_wait_status::__timeout;
+ }
+
+ struct __timed_waiters : __waiters
+ {
+ template<typename _Clock, typename _Duration>
+ __atomic_wait_status
+ _M_do_wait_until(__platform_wait_t __version,
+ const chrono::time_point<_Clock, _Duration>& __atime)
+ {
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+ return __platform_wait_until(&_M_ver, __version, __atime);
+#else
+ __platform_wait_t __cur = 0;
+ __waiters::__lock_t __l(_M_mtx);
+ while (__cur <= __version)
+ {
+ if (__cond_wait_until(&_M_cv, __l, __atime) ==
__atomic_wait_status::__timeout)
Qualify.
+ return __atomic_wait_status::__timeout;
+
+ __platform_wait_t __last = __cur;
+ __atomic_load(&_M_ver, &__cur, __ATOMIC_ACQUIRE);
+ if (__cur < __last)
+ break; // break the loop if version overflows
+ }
+ return __atomic_wait_status::__no_timeout;
+#endif
+ }
+
+ static __timed_waiters&
+ _S_timed_for(void* __t)
+ {
+ static_assert(sizeof(__timed_waiters) == sizeof(__waiters));
+ return (__timed_waiters&) __waiters::_S_for(__t);
I'd be more comfortable with a static_cast here.
+ }
+ };
+ } // namespace __detail
+
+ template<typename _Tp, typename _Pred,
+ typename _Clock, typename _Duration>
+ bool
+ __atomic_wait_until(const _Tp* __addr, _Tp __old, _Pred __pred,
+ const chrono::time_point<_Clock, _Duration>& __atime)
noexcept
+ {
+ using namespace __detail;
+
+ if (std::__atomic_spin(__pred))
+ return true;
+
+ auto& __w = __timed_waiters::_S_timed_for((void*)__addr);
+ auto __version = __w._M_enter_wait();
+ do
+ {
+ __atomic_wait_status __res;
+ if constexpr (__platform_wait_uses_type<_Tp>)
+ {
+ __res = __platform_wait_until((__platform_wait_t*)(void*) __addr,
+ __old,
+ __atime);
+ }
+ else
+ {
+ __res = __w._M_do_wait_until(__version, __atime);
+ }
+ if (__res == __atomic_wait_status::__timeout)
+ return false;
+ }
+ while (!__pred() && __atime < _Clock::now());
+ __w._M_leave_wait();
+
+ // if timed out, return false
+ return (_Clock::now() < __atime);
+ }
+
+ template<typename _Tp, typename _Pred,
+ typename _Rep, typename _Period>
+ bool
+ __atomic_wait_for(const _Tp* __addr, _Tp __old, _Pred __pred,
+ const chrono::duration<_Rep, _Period>& __rtime) noexcept
+ {
+ using namespace __detail;
+
+ if (std::__atomic_spin(__pred))
+ return true;
+
+ if (!__rtime.count())
+ return false; // no rtime supplied, and spin did not acquire
+
+ using __dur = chrono::steady_clock::duration;
+ auto __reltime = chrono::duration_cast<__dur>(__rtime);
+ if (__reltime < __rtime)
+ ++__reltime;
+
+
+ return __atomic_wait_until(__addr, __old, std::move(__pred),
+ chrono::steady_clock::now() + __reltime);
+ }
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+#endif
diff --git a/libstdc++-v3/include/bits/atomic_wait.h
b/libstdc++-v3/include/bits/atomic_wait.h
new file mode 100644
index 00000000000..92c1e2526ed
--- /dev/null
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -0,0 +1,291 @@
+// -*- C++ -*- header.
+
+// Copyright (C) 2020 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_wait.h
+ * This is an internal header file, included by other library headers.
+ * Do not attempt to use it directly. @headername{atomic}
+ */
+
+#ifndef _GLIBCXX_ATOMIC_WAIT_H
+#define _GLIBCXX_ATOMIC_WAIT_H 1
+
+#pragma GCC system_header
+
+#include <bits/c++config.h>
+#include <bits/functional_hash.h>
+#include <bits/gthr.h>
+#include <bits/std_mutex.h>
+#include <bits/unique_lock.h>
+#include <ext/numeric_traits.h>
+
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+#include <climits>
+#include <unistd.h>
+#include <syscall.h>
+#endif
+
+#define _GLIBCXX_SPIN_COUNT_1 16
+#define _GLIBCXX_SPIN_COUNT_2 12
+
Yuck, do these have to be macros?
+// TODO get this from Autoconf
+#define _GLIBCXX_HAVE_LINUX_FUTEX_PRIVATE 1
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+ namespace __detail
+ {
+ using __platform_wait_t = int;
+
+ inline constexpr
+ auto __platform_wait_max_value =
+ __gnu_cxx::__numeric_traits<__platform_wait_t>::__max;
You can usee the new __gnu_cxx::__int_traits alias here, since you
know __platform_wait_t is an integer, not a floating-point type. That
alias just saves instantiating __numeric_traits to figure out whether
to use __numeric_traits_integer or __numeric_traits_floating.
+
+ template<typename _Tp>
+ inline constexpr bool __platform_wait_uses_type
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+ = is_same_v<remove_cv_t<_Tp>, __platform_wait_t>;
+#else
+ = false;
+#endif
+
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+ enum
See earlier comment about unnamed enum types.
+ {
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX_PRIVATE
+ __futex_private_flag = 128,
+#else
+ __futex_private_flag = 0,
+#endif
+ __futex_wait = 0,
+ __futex_wake = 1,
+ __futex_wait_bitset = 9,
+ __futex_wake_bitset = 10,
+ __futex_wait_private = __futex_wait | __futex_private_flag,
+ __futex_wake_private = __futex_wake | __futex_private_flag
+ };
+
+ void
+ __platform_wait(__platform_wait_t* __addr, __platform_wait_t __val)
noexcept
+ {
+ auto __e = syscall (SYS_futex, __addr, __futex_wait_private, __val,
nullptr);
+ if (__e && !(errno == EINTR || errno == EAGAIN))
+ std::terminate();
+ }
+
+ void
+ __platform_notify(__platform_wait_t* __addr, bool __all) noexcept
+ {
+ syscall (SYS_futex, __addr, __futex_wake_private, __all ? INT_MAX : 1);
+ }
+#endif
+
+ struct __waiters
+ {
+ __platform_wait_t alignas(64) _M_ver = 0;
+ __platform_wait_t alignas(64) _M_wait = 0;
+
+#ifndef _GLIBCXX_HAVE_LINUX_FUTEX
+ using __lock_t = std::unique_lock<std::mutex>;
+ mutable __lock_t::mutex_type _M_mtx;
+
+# ifdef __GTHREAD_COND_INIT
+ mutable __gthread_cond_t _M_cv = __GTHREAD_COND_INIT;
Not being able to use std::condition_variable here makes me sad.
+ __waiters() noexcept = default;
+# else
+ mutable __gthread_cond_t _M_cv;
+ __waiters() noexcept
+ {
+ __GTHREAD_COND_INIT_FUNCTION(&_M_cond);
+ }
+# endif
+#endif
+
+ __platform_wait_t
+ _M_enter_wait() noexcept
+ {
+ __platform_wait_t __res;
+ __atomic_load(&_M_ver, &__res, __ATOMIC_ACQUIRE);
+ __atomic_fetch_add(&_M_wait, 1, __ATOMIC_ACQ_REL);
+ return __res;
+ }
+
+ void
+ _M_leave_wait() noexcept
+ {
+ __atomic_fetch_sub(&_M_wait, 1, __ATOMIC_ACQ_REL);
+ }
+
+ void
+ _M_do_wait(__platform_wait_t __version) noexcept
+ {
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+ __platform_wait(&_M_ver, __version);
+#else
+ __platform_wait_t __cur = 0;
+ while (__cur <= __version)
+ {
+ __waiters::__lock_t __l(_M_mtx);
+ auto __e = __gthread_cond_wait(&_M_cv,
__l.mutex()->native_handle());
+ if (__e)
+ std::terminate();
+ __platform_wait_t __last = __cur;
+ __atomic_load(&_M_ver, &__cur, __ATOMIC_ACQUIRE);
+ if (__cur < __last)
+ break; // break the loop if version overflows
+ }
+#endif
+ }
+
+ __platform_wait_t
+ _M_waiting() const noexcept
+ {
+ __platform_wait_t __res;
+ __atomic_load(&_M_wait, &__res, __ATOMIC_ACQUIRE);
+ return __res;
+ }
+
+ void
+ _M_notify(bool __all) noexcept
+ {
+ __atomic_fetch_add(&_M_ver, 1, __ATOMIC_ACQ_REL);
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+ __platform_notify(&_M_ver, __all);
+#else
+ auto __e = __gthread_cond_broadcast(&_M_cv);
+ if (__e)
+ __throw_system_error(__e);
+#endif
+ }
+
+ static __waiters&
+ _S_for(void* __t)
+ {
+ const unsigned char __mask = 0xf;
+ static __waiters __w[__mask + 1];
+
+ auto __key = _Hash_impl::hash(__t) & __mask;
+ return __w[__key];
+ }
+ };
+
+ struct __waiter
+ {
+ __waiters& _M_w;
+ __platform_wait_t _M_version;
+
+ template<typename _Tp>
+ __waiter(const _Tp* __addr) noexcept
+ : _M_w(__waiters::_S_for((void*) __addr))
+ , _M_version(_M_w._M_enter_wait())
+ { }
+
+ ~__waiter()
+ { _M_w._M_leave_wait(); }
+
+ void _M_do_wait() noexcept
+ { _M_w._M_do_wait(_M_version); }
+ };
+
+ void
+ __thread_relax() noexcept
+ {
+#if defined __i386__ || defined __x86_64__
+ __builtin_ia32_pause();
+#elif defined _GLIBCXX_USE_SCHED_YIELD
+ __gthread_yield();
+#endif
Should this and the identical code in <stop_token> be consolidated
somewhere?
+ }
+
+ void
+ __thread_yield() noexcept
+ {
+#if defined _GLIBCXX_USE_SCHED_YIELD
+ __gthread_yield();
+#endif
+ }
+
+ } // namespace __detail
+
+ template<typename _Pred>
+ bool
+ __atomic_spin(_Pred __pred) noexcept
+ {
+ for (auto __i = 0; __i < _GLIBCXX_SPIN_COUNT_1; ++__i)
+ {
+ if (__pred())
+ return true;
+
+ if (__i < _GLIBCXX_SPIN_COUNT_2)
+ __detail::__thread_relax();
+ else
+ __detail::__thread_yield();
+ }
+ return false;
+ }
+
+ template<typename _Tp, typename _Pred>
+ void
+ __atomic_wait(const _Tp* __addr, _Tp __old, _Pred __pred) noexcept
+ {
+ using namespace __detail;
+ if (__atomic_spin(__pred))
+ return;
+
+ __waiter __w(__addr);
+ while (!__pred())
+ {
+ if constexpr (__platform_wait_uses_type<_Tp>)
+ {
+ __platform_wait((__platform_wait_t*)(void*) __addr, __old);
This has an implicit conversion from _To to __platform_wait_t, is that
safe? Can we make it explicit with a static_cast?
+ }
+ else
+ {
+ // TODO support timed backoff when this can be moved into the lib
+ __w._M_do_wait();
+ }
+ }
+ }
+
+ template<typename _Tp>
+ void
+ __atomic_notify(const _Tp* __addr, bool __all) noexcept
+ {
+ using namespace __detail;
+ auto& __w = __waiters::_S_for((void*)__addr);
+ if (!__w._M_waiting())
+ return;
+
+ if constexpr (__platform_wait_uses_type<_Tp>)
+ {
+ __platform_notify((__platform_wait_t*)(void*) __addr, __all);
+ }
+ else
+ {
+ __w._M_notify(__all);
+ }
+ }
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+#endif
diff --git a/libstdc++-v3/include/bits/semaphore_base.h
b/libstdc++-v3/include/bits/semaphore_base.h
new file mode 100644
index 00000000000..f0c4235d91c
--- /dev/null
+++ b/libstdc++-v3/include/bits/semaphore_base.h
I'll continue reviewing from here ASAP ...
