151154a21d
We have a comment saying to replace the simple binary_semaphore type with std::binary_semaphore, which has been done. However, that isn't defined on all targets. So keep the simple one here that just implements the parts of the API needed by <stop_token>, and remove the comment suggesting it should be replaced. libstdc++-v3/ChangeLog: * include/std/stop_token: Remove TODO comment.
652 lines
16 KiB
C++
652 lines
16 KiB
C++
// <stop_token> -*- C++ -*-
|
|
|
|
// Copyright (C) 2019-2021 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/>.
|
|
|
|
/** @file include/stop_token
|
|
* This is a Standard C++ Library header.
|
|
*/
|
|
|
|
#ifndef _GLIBCXX_STOP_TOKEN
|
|
#define _GLIBCXX_STOP_TOKEN
|
|
|
|
#if __cplusplus > 201703L
|
|
|
|
#include <atomic>
|
|
#include <bits/std_thread.h>
|
|
|
|
#include <semaphore>
|
|
|
|
#define __cpp_lib_jthread 201911L
|
|
|
|
namespace std _GLIBCXX_VISIBILITY(default)
|
|
{
|
|
_GLIBCXX_BEGIN_NAMESPACE_VERSION
|
|
|
|
/// Tag type indicating a stop_source should have no shared-stop-state.
|
|
struct nostopstate_t { explicit nostopstate_t() = default; };
|
|
inline constexpr nostopstate_t nostopstate{};
|
|
|
|
class stop_source;
|
|
|
|
/// Allow testing whether a stop request has been made on a `stop_source`.
|
|
class stop_token
|
|
{
|
|
public:
|
|
stop_token() noexcept = default;
|
|
|
|
stop_token(const stop_token&) noexcept = default;
|
|
stop_token(stop_token&&) noexcept = default;
|
|
|
|
~stop_token() = default;
|
|
|
|
stop_token&
|
|
operator=(const stop_token&) noexcept = default;
|
|
|
|
stop_token&
|
|
operator=(stop_token&&) noexcept = default;
|
|
|
|
[[nodiscard]]
|
|
bool
|
|
stop_possible() const noexcept
|
|
{
|
|
return static_cast<bool>(_M_state) && _M_state->_M_stop_possible();
|
|
}
|
|
|
|
[[nodiscard]]
|
|
bool
|
|
stop_requested() const noexcept
|
|
{
|
|
return static_cast<bool>(_M_state) && _M_state->_M_stop_requested();
|
|
}
|
|
|
|
void
|
|
swap(stop_token& __rhs) noexcept
|
|
{ _M_state.swap(__rhs._M_state); }
|
|
|
|
[[nodiscard]]
|
|
friend bool
|
|
operator==(const stop_token& __a, const stop_token& __b)
|
|
{ return __a._M_state == __b._M_state; }
|
|
|
|
friend void
|
|
swap(stop_token& __lhs, stop_token& __rhs) noexcept
|
|
{ __lhs.swap(__rhs); }
|
|
|
|
private:
|
|
friend class stop_source;
|
|
template<typename _Callback>
|
|
friend class stop_callback;
|
|
|
|
static void
|
|
_S_yield() noexcept
|
|
{
|
|
#if defined __i386__ || defined __x86_64__
|
|
__builtin_ia32_pause();
|
|
#endif
|
|
this_thread::yield();
|
|
}
|
|
|
|
#ifndef __cpp_lib_semaphore
|
|
struct binary_semaphore
|
|
{
|
|
explicit binary_semaphore(int __d) : _M_counter(__d > 0) { }
|
|
|
|
void release() { _M_counter.fetch_add(1, memory_order::release); }
|
|
|
|
void acquire()
|
|
{
|
|
int __old = 1;
|
|
while (!_M_counter.compare_exchange_weak(__old, 0,
|
|
memory_order::acquire,
|
|
memory_order::relaxed))
|
|
{
|
|
__old = 1;
|
|
_S_yield();
|
|
}
|
|
}
|
|
|
|
atomic<int> _M_counter;
|
|
};
|
|
#endif
|
|
|
|
struct _Stop_cb
|
|
{
|
|
using __cb_type = void(_Stop_cb*) noexcept;
|
|
__cb_type* _M_callback;
|
|
_Stop_cb* _M_prev = nullptr;
|
|
_Stop_cb* _M_next = nullptr;
|
|
bool* _M_destroyed = nullptr;
|
|
binary_semaphore _M_done{0};
|
|
|
|
[[__gnu__::__nonnull__]]
|
|
explicit
|
|
_Stop_cb(__cb_type* __cb)
|
|
: _M_callback(__cb)
|
|
{ }
|
|
|
|
void _M_run() noexcept { _M_callback(this); }
|
|
};
|
|
|
|
struct _Stop_state_t
|
|
{
|
|
using value_type = uint32_t;
|
|
static constexpr value_type _S_stop_requested_bit = 1;
|
|
static constexpr value_type _S_locked_bit = 2;
|
|
static constexpr value_type _S_ssrc_counter_inc = 4;
|
|
|
|
std::atomic<value_type> _M_owners{1};
|
|
std::atomic<value_type> _M_value{_S_ssrc_counter_inc};
|
|
_Stop_cb* _M_head = nullptr;
|
|
std::thread::id _M_requester;
|
|
|
|
_Stop_state_t() = default;
|
|
|
|
bool
|
|
_M_stop_possible() noexcept
|
|
{
|
|
// true if a stop request has already been made or there are still
|
|
// stop_source objects that would allow one to be made.
|
|
return _M_value.load(memory_order::acquire) & ~_S_locked_bit;
|
|
}
|
|
|
|
bool
|
|
_M_stop_requested() noexcept
|
|
{
|
|
return _M_value.load(memory_order::acquire) & _S_stop_requested_bit;
|
|
}
|
|
|
|
void
|
|
_M_add_owner() noexcept
|
|
{
|
|
_M_owners.fetch_add(1, memory_order::relaxed);
|
|
}
|
|
|
|
void
|
|
_M_release_ownership() noexcept
|
|
{
|
|
if (_M_owners.fetch_sub(1, memory_order::acq_rel) == 1)
|
|
delete this;
|
|
}
|
|
|
|
void
|
|
_M_add_ssrc() noexcept
|
|
{
|
|
_M_value.fetch_add(_S_ssrc_counter_inc, memory_order::relaxed);
|
|
}
|
|
|
|
void
|
|
_M_sub_ssrc() noexcept
|
|
{
|
|
_M_value.fetch_sub(_S_ssrc_counter_inc, memory_order::release);
|
|
}
|
|
|
|
// Obtain lock.
|
|
void
|
|
_M_lock() noexcept
|
|
{
|
|
// Can use relaxed loads to get the current value.
|
|
// The successful call to _M_try_lock is an acquire operation.
|
|
auto __old = _M_value.load(memory_order::relaxed);
|
|
while (!_M_try_lock(__old, memory_order::relaxed))
|
|
{ }
|
|
}
|
|
|
|
// Precondition: calling thread holds the lock.
|
|
void
|
|
_M_unlock() noexcept
|
|
{
|
|
_M_value.fetch_sub(_S_locked_bit, memory_order::release);
|
|
}
|
|
|
|
bool
|
|
_M_request_stop() noexcept
|
|
{
|
|
// obtain lock and set stop_requested bit
|
|
auto __old = _M_value.load(memory_order::acquire);
|
|
do
|
|
{
|
|
if (__old & _S_stop_requested_bit) // stop request already made
|
|
return false;
|
|
}
|
|
while (!_M_try_lock_and_stop(__old));
|
|
|
|
_M_requester = this_thread::get_id();
|
|
|
|
while (_M_head)
|
|
{
|
|
bool __last_cb;
|
|
_Stop_cb* __cb = _M_head;
|
|
_M_head = _M_head->_M_next;
|
|
if (_M_head)
|
|
{
|
|
_M_head->_M_prev = nullptr;
|
|
__last_cb = false;
|
|
}
|
|
else
|
|
__last_cb = true;
|
|
|
|
// Allow other callbacks to be unregistered while __cb runs.
|
|
_M_unlock();
|
|
|
|
bool __destroyed = false;
|
|
__cb->_M_destroyed = &__destroyed;
|
|
|
|
// run callback
|
|
__cb->_M_run();
|
|
|
|
if (!__destroyed)
|
|
{
|
|
__cb->_M_destroyed = nullptr;
|
|
|
|
// synchronize with destructor of stop_callback that owns *__cb
|
|
if (!__gnu_cxx::__is_single_threaded())
|
|
__cb->_M_done.release();
|
|
}
|
|
|
|
// Avoid relocking if we already know there are no more callbacks.
|
|
if (__last_cb)
|
|
return true;
|
|
|
|
_M_lock();
|
|
}
|
|
|
|
_M_unlock();
|
|
return true;
|
|
}
|
|
|
|
[[__gnu__::__nonnull__]]
|
|
bool
|
|
_M_register_callback(_Stop_cb* __cb) noexcept
|
|
{
|
|
auto __old = _M_value.load(memory_order::acquire);
|
|
do
|
|
{
|
|
if (__old & _S_stop_requested_bit) // stop request already made
|
|
{
|
|
__cb->_M_run(); // run synchronously
|
|
return false;
|
|
}
|
|
|
|
if (__old < _S_ssrc_counter_inc) // no stop_source owns *this
|
|
// No need to register callback if no stop request can be made.
|
|
// Returning false also means the stop_callback does not share
|
|
// ownership of this state, but that's not observable.
|
|
return false;
|
|
}
|
|
while (!_M_try_lock(__old));
|
|
|
|
__cb->_M_next = _M_head;
|
|
if (_M_head)
|
|
{
|
|
_M_head->_M_prev = __cb;
|
|
}
|
|
_M_head = __cb;
|
|
_M_unlock();
|
|
return true;
|
|
}
|
|
|
|
// Called by ~stop_callback just before destroying *__cb.
|
|
[[__gnu__::__nonnull__]]
|
|
void
|
|
_M_remove_callback(_Stop_cb* __cb)
|
|
{
|
|
_M_lock();
|
|
|
|
if (__cb == _M_head)
|
|
{
|
|
_M_head = _M_head->_M_next;
|
|
if (_M_head)
|
|
_M_head->_M_prev = nullptr;
|
|
_M_unlock();
|
|
return;
|
|
}
|
|
else if (__cb->_M_prev)
|
|
{
|
|
__cb->_M_prev->_M_next = __cb->_M_next;
|
|
if (__cb->_M_next)
|
|
__cb->_M_next->_M_prev = __cb->_M_prev;
|
|
_M_unlock();
|
|
return;
|
|
}
|
|
|
|
_M_unlock();
|
|
|
|
// Callback is not in the list, so must have been removed by a call to
|
|
// _M_request_stop.
|
|
|
|
// Despite appearances there is no data race on _M_requester. The only
|
|
// write to it happens before the callback is removed from the list,
|
|
// and removing it from the list happens before this read.
|
|
if (!(_M_requester == this_thread::get_id()))
|
|
{
|
|
// Synchronize with completion of callback.
|
|
__cb->_M_done.acquire();
|
|
// Safe for ~stop_callback to destroy *__cb now.
|
|
return;
|
|
}
|
|
|
|
if (__cb->_M_destroyed)
|
|
*__cb->_M_destroyed = true;
|
|
}
|
|
|
|
// Try to obtain the lock.
|
|
// Returns true if the lock is acquired (with memory order acquire).
|
|
// Otherwise, sets __curval = _M_value.load(__failure) and returns false.
|
|
// Might fail spuriously, so must be called in a loop.
|
|
bool
|
|
_M_try_lock(value_type& __curval,
|
|
memory_order __failure = memory_order::acquire) noexcept
|
|
{
|
|
return _M_do_try_lock(__curval, 0, memory_order::acquire, __failure);
|
|
}
|
|
|
|
// Try to obtain the lock to make a stop request.
|
|
// Returns true if the lock is acquired and the _S_stop_requested_bit is
|
|
// set (with memory order acq_rel so that other threads see the request).
|
|
// Otherwise, sets __curval = _M_value.load(memory_order::acquire) and
|
|
// returns false.
|
|
// Might fail spuriously, so must be called in a loop.
|
|
bool
|
|
_M_try_lock_and_stop(value_type& __curval) noexcept
|
|
{
|
|
return _M_do_try_lock(__curval, _S_stop_requested_bit,
|
|
memory_order::acq_rel, memory_order::acquire);
|
|
}
|
|
|
|
bool
|
|
_M_do_try_lock(value_type& __curval, value_type __newbits,
|
|
memory_order __success, memory_order __failure) noexcept
|
|
{
|
|
if (__curval & _S_locked_bit)
|
|
{
|
|
_S_yield();
|
|
__curval = _M_value.load(__failure);
|
|
return false;
|
|
}
|
|
__newbits |= _S_locked_bit;
|
|
return _M_value.compare_exchange_weak(__curval, __curval | __newbits,
|
|
__success, __failure);
|
|
}
|
|
};
|
|
|
|
struct _Stop_state_ref
|
|
{
|
|
_Stop_state_ref() = default;
|
|
|
|
explicit
|
|
_Stop_state_ref(const stop_source&)
|
|
: _M_ptr(new _Stop_state_t())
|
|
{ }
|
|
|
|
_Stop_state_ref(const _Stop_state_ref& __other) noexcept
|
|
: _M_ptr(__other._M_ptr)
|
|
{
|
|
if (_M_ptr)
|
|
_M_ptr->_M_add_owner();
|
|
}
|
|
|
|
_Stop_state_ref(_Stop_state_ref&& __other) noexcept
|
|
: _M_ptr(__other._M_ptr)
|
|
{
|
|
__other._M_ptr = nullptr;
|
|
}
|
|
|
|
_Stop_state_ref&
|
|
operator=(const _Stop_state_ref& __other) noexcept
|
|
{
|
|
if (auto __ptr = __other._M_ptr; __ptr != _M_ptr)
|
|
{
|
|
if (__ptr)
|
|
__ptr->_M_add_owner();
|
|
if (_M_ptr)
|
|
_M_ptr->_M_release_ownership();
|
|
_M_ptr = __ptr;
|
|
}
|
|
return *this;
|
|
}
|
|
|
|
_Stop_state_ref&
|
|
operator=(_Stop_state_ref&& __other) noexcept
|
|
{
|
|
_Stop_state_ref(std::move(__other)).swap(*this);
|
|
return *this;
|
|
}
|
|
|
|
~_Stop_state_ref()
|
|
{
|
|
if (_M_ptr)
|
|
_M_ptr->_M_release_ownership();
|
|
}
|
|
|
|
void
|
|
swap(_Stop_state_ref& __other) noexcept
|
|
{ std::swap(_M_ptr, __other._M_ptr); }
|
|
|
|
explicit operator bool() const noexcept { return _M_ptr != nullptr; }
|
|
|
|
_Stop_state_t* operator->() const noexcept { return _M_ptr; }
|
|
|
|
#if __cpp_impl_three_way_comparison >= 201907L
|
|
friend bool
|
|
operator==(const _Stop_state_ref&, const _Stop_state_ref&) = default;
|
|
#else
|
|
friend bool
|
|
operator==(const _Stop_state_ref& __lhs, const _Stop_state_ref& __rhs)
|
|
noexcept
|
|
{ return __lhs._M_ptr == __rhs._M_ptr; }
|
|
|
|
friend bool
|
|
operator!=(const _Stop_state_ref& __lhs, const _Stop_state_ref& __rhs)
|
|
noexcept
|
|
{ return __lhs._M_ptr != __rhs._M_ptr; }
|
|
#endif
|
|
|
|
private:
|
|
_Stop_state_t* _M_ptr = nullptr;
|
|
};
|
|
|
|
_Stop_state_ref _M_state;
|
|
|
|
explicit
|
|
stop_token(const _Stop_state_ref& __state) noexcept
|
|
: _M_state{__state}
|
|
{ }
|
|
};
|
|
|
|
/// A type that allows a stop request to be made.
|
|
class stop_source
|
|
{
|
|
public:
|
|
stop_source() : _M_state(*this)
|
|
{ }
|
|
|
|
explicit stop_source(std::nostopstate_t) noexcept
|
|
{ }
|
|
|
|
stop_source(const stop_source& __other) noexcept
|
|
: _M_state(__other._M_state)
|
|
{
|
|
if (_M_state)
|
|
_M_state->_M_add_ssrc();
|
|
}
|
|
|
|
stop_source(stop_source&&) noexcept = default;
|
|
|
|
stop_source&
|
|
operator=(const stop_source& __other) noexcept
|
|
{
|
|
if (_M_state != __other._M_state)
|
|
{
|
|
stop_source __sink(std::move(*this));
|
|
_M_state = __other._M_state;
|
|
if (_M_state)
|
|
_M_state->_M_add_ssrc();
|
|
}
|
|
return *this;
|
|
}
|
|
|
|
stop_source&
|
|
operator=(stop_source&&) noexcept = default;
|
|
|
|
~stop_source()
|
|
{
|
|
if (_M_state)
|
|
_M_state->_M_sub_ssrc();
|
|
}
|
|
|
|
[[nodiscard]]
|
|
bool
|
|
stop_possible() const noexcept
|
|
{
|
|
return static_cast<bool>(_M_state);
|
|
}
|
|
|
|
[[nodiscard]]
|
|
bool
|
|
stop_requested() const noexcept
|
|
{
|
|
return static_cast<bool>(_M_state) && _M_state->_M_stop_requested();
|
|
}
|
|
|
|
bool
|
|
request_stop() const noexcept
|
|
{
|
|
if (stop_possible())
|
|
return _M_state->_M_request_stop();
|
|
return false;
|
|
}
|
|
|
|
[[nodiscard]]
|
|
stop_token
|
|
get_token() const noexcept
|
|
{
|
|
return stop_token{_M_state};
|
|
}
|
|
|
|
void
|
|
swap(stop_source& __other) noexcept
|
|
{
|
|
_M_state.swap(__other._M_state);
|
|
}
|
|
|
|
[[nodiscard]]
|
|
friend bool
|
|
operator==(const stop_source& __a, const stop_source& __b) noexcept
|
|
{
|
|
return __a._M_state == __b._M_state;
|
|
}
|
|
|
|
friend void
|
|
swap(stop_source& __lhs, stop_source& __rhs) noexcept
|
|
{
|
|
__lhs.swap(__rhs);
|
|
}
|
|
|
|
private:
|
|
stop_token::_Stop_state_ref _M_state;
|
|
};
|
|
|
|
/// A wrapper for callbacks to be run when a stop request is made.
|
|
template<typename _Callback>
|
|
class [[nodiscard]] stop_callback
|
|
{
|
|
static_assert(is_nothrow_destructible_v<_Callback>);
|
|
static_assert(is_invocable_v<_Callback>);
|
|
|
|
public:
|
|
using callback_type = _Callback;
|
|
|
|
template<typename _Cb,
|
|
enable_if_t<is_constructible_v<_Callback, _Cb>, int> = 0>
|
|
explicit
|
|
stop_callback(const stop_token& __token, _Cb&& __cb)
|
|
noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
|
|
: _M_cb(std::forward<_Cb>(__cb))
|
|
{
|
|
if (auto __state = __token._M_state)
|
|
{
|
|
if (__state->_M_register_callback(&_M_cb))
|
|
_M_state.swap(__state);
|
|
}
|
|
}
|
|
|
|
template<typename _Cb,
|
|
enable_if_t<is_constructible_v<_Callback, _Cb>, int> = 0>
|
|
explicit
|
|
stop_callback(stop_token&& __token, _Cb&& __cb)
|
|
noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
|
|
: _M_cb(std::forward<_Cb>(__cb))
|
|
{
|
|
if (auto& __state = __token._M_state)
|
|
{
|
|
if (__state->_M_register_callback(&_M_cb))
|
|
_M_state.swap(__state);
|
|
}
|
|
}
|
|
|
|
~stop_callback()
|
|
{
|
|
if (_M_state)
|
|
{
|
|
_M_state->_M_remove_callback(&_M_cb);
|
|
}
|
|
}
|
|
|
|
stop_callback(const stop_callback&) = delete;
|
|
stop_callback& operator=(const stop_callback&) = delete;
|
|
stop_callback(stop_callback&&) = delete;
|
|
stop_callback& operator=(stop_callback&&) = delete;
|
|
|
|
private:
|
|
struct _Cb_impl : stop_token::_Stop_cb
|
|
{
|
|
template<typename _Cb>
|
|
explicit
|
|
_Cb_impl(_Cb&& __cb)
|
|
: _Stop_cb(&_S_execute),
|
|
_M_cb(std::forward<_Cb>(__cb))
|
|
{ }
|
|
|
|
_Callback _M_cb;
|
|
|
|
[[__gnu__::__nonnull__]]
|
|
static void
|
|
_S_execute(_Stop_cb* __that) noexcept
|
|
{
|
|
_Callback& __cb = static_cast<_Cb_impl*>(__that)->_M_cb;
|
|
std::forward<_Callback>(__cb)();
|
|
}
|
|
};
|
|
|
|
_Cb_impl _M_cb;
|
|
stop_token::_Stop_state_ref _M_state;
|
|
};
|
|
|
|
template<typename _Callback>
|
|
stop_callback(stop_token, _Callback) -> stop_callback<_Callback>;
|
|
|
|
_GLIBCXX_END_NAMESPACE_VERSION
|
|
} // namespace
|
|
#endif // __cplusplus > 201703L
|
|
#endif // _GLIBCXX_STOP_TOKEN
|