// <mutex> -*- C++ -*-
// Copyright (C) 2003-2023 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/mutex
* This is a Standard C++ Library header.
*/
#ifndef _GLIBCXX_MUTEX
#define _GLIBCXX_MUTEX 1
#pragma GCC system_header
#include <bits/requires_hosted.h> // concurrency
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
#include <tuple>
#include <exception>
#include <type_traits>
#include <bits/chrono.h>
#include <bits/error_constants.h>
#include <bits/std_mutex.h>
#include <bits/unique_lock.h>
#if ! _GTHREAD_USE_MUTEX_TIMEDLOCK
# include <condition_variable>
# include <thread>
#endif
#include <ext/atomicity.h> // __gnu_cxx::__is_single_threaded
#if defined _GLIBCXX_HAS_GTHREADS && ! defined _GLIBCXX_HAVE_TLS
# include <bits/std_function.h> // std::function
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @addtogroup mutexes
* @{
*/
#ifdef _GLIBCXX_HAS_GTHREADS
/// @cond undocumented
// Common base class for std::recursive_mutex and std::recursive_timed_mutex
class __recursive_mutex_base
{
protected:
typedef __gthread_recursive_mutex_t __native_type;
__recursive_mutex_base(const __recursive_mutex_base&) = delete;
__recursive_mutex_base& operator=(const __recursive_mutex_base&) = delete;
#ifdef __GTHREAD_RECURSIVE_MUTEX_INIT
__native_type _M_mutex = __GTHREAD_RECURSIVE_MUTEX_INIT;
__recursive_mutex_base() = default;
#else
__native_type _M_mutex;
__recursive_mutex_base()
{
// XXX EAGAIN, ENOMEM, EPERM, EBUSY(may), EINVAL(may)
__GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION(&_M_mutex);
}
~__recursive_mutex_base()
{ __gthread_recursive_mutex_destroy(&_M_mutex); }
#endif
};
/// @endcond
/** The standard recursive mutex type.
*
* A recursive mutex can be locked more than once by the same thread.
* Other threads cannot lock the mutex until the owning thread unlocks it
* as many times as it was locked.
*
* @headerfile mutex
* @since C++11
*/
class recursive_mutex : private __recursive_mutex_base
{
public:
typedef __native_type* native_handle_type;
recursive_mutex() = default;
~recursive_mutex() = default;
recursive_mutex(const recursive_mutex&) = delete;
recursive_mutex& operator=(const recursive_mutex&) = delete;
void
lock()
{
int __e = __gthread_recursive_mutex_lock(&_M_mutex);
// EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
if (__e)
__throw_system_error(__e);
}
_GLIBCXX_NODISCARD
bool
try_lock() noexcept
{
// XXX EINVAL, EAGAIN, EBUSY
return !__gthread_recursive_mutex_trylock(&_M_mutex);
}
void
unlock()
{
// XXX EINVAL, EAGAIN, EBUSY
__gthread_recursive_mutex_unlock(&_M_mutex);
}
native_handle_type
native_handle() noexcept
{ return &_M_mutex; }
};
#if _GTHREAD_USE_MUTEX_TIMEDLOCK
/// @cond undocumented
template<typename _Derived>
class __timed_mutex_impl
{
protected:
template<typename _Rep, typename _Period>
bool
_M_try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
{
#if _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
using __clock = chrono::steady_clock;
#else
using __clock = chrono::system_clock;
#endif
auto __rt = chrono::duration_cast<__clock::duration>(__rtime);
if (ratio_greater<__clock::period, _Period>())
++__rt;
return _M_try_lock_until(__clock::now() + __rt);
}
template<typename _Duration>
bool
_M_try_lock_until(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())
};
return static_cast<_Derived*>(this)->_M_timedlock(__ts);
}
#ifdef _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
template<typename _Duration>
bool
_M_try_lock_until(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())
};
return static_cast<_Derived*>(this)->_M_clocklock(CLOCK_MONOTONIC,
__ts);
}
#endif
template<typename _Clock, typename _Duration>
bool
_M_try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
{
#if __cplusplus > 201703L
static_assert(chrono::is_clock_v<_Clock>);
#endif
// The user-supplied clock may not tick at the same rate as
// steady_clock, so we must loop in order to guarantee that
// the timeout has expired before returning false.
auto __now = _Clock::now();
do {
auto __rtime = __atime - __now;
if (_M_try_lock_for(__rtime))
return true;
__now = _Clock::now();
} while (__atime > __now);
return false;
}
};
/// @endcond
/** The standard timed mutex type.
*
* A non-recursive mutex that supports a timeout when trying to acquire the
* lock.
*
* @headerfile mutex
* @since C++11
*/
class timed_mutex
: private __mutex_base, public __timed_mutex_impl<timed_mutex>
{
public:
typedef __native_type* native_handle_type;
timed_mutex() = default;
~timed_mutex() = default;
timed_mutex(const timed_mutex&) = delete;
timed_mutex& operator=(const timed_mutex&) = delete;
void
lock()
{
int __e = __gthread_mutex_lock(&_M_mutex);
// EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
if (__e)
__throw_system_error(__e);
}
_GLIBCXX_NODISCARD
bool
try_lock() noexcept
{
// XXX EINVAL, EAGAIN, EBUSY
return !__gthread_mutex_trylock(&_M_mutex);
}
template <class _Rep, class _Period>
_GLIBCXX_NODISCARD
bool
try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
{ return _M_try_lock_for(__rtime); }
template <class _Clock, class _Duration>
_GLIBCXX_NODISCARD
bool
try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
{ return _M_try_lock_until(__atime); }
void
unlock()
{
// XXX EINVAL, EAGAIN, EBUSY
__gthread_mutex_unlock(&_M_mutex);
}
native_handle_type
native_handle() noexcept
{ return &_M_mutex; }
private:
friend class __timed_mutex_impl<timed_mutex>;
bool
_M_timedlock(const __gthread_time_t& __ts)
{ return !__gthread_mutex_timedlock(&_M_mutex, &__ts); }
#if _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
bool
_M_clocklock(clockid_t __clockid, const __gthread_time_t& __ts)
{ return !pthread_mutex_clocklock(&_M_mutex, __clockid, &__ts); }
#endif
};
/** The standard recursive timed mutex type.
*
* A recursive mutex that supports a timeout when trying to acquire the
* lock. A recursive mutex can be locked more than once by the same thread.
* Other threads cannot lock the mutex until the owning thread unlocks it
* as many times as it was locked.
*
* @headerfile mutex
* @since C++11
*/
class recursive_timed_mutex
: private __recursive_mutex_base,
public __timed_mutex_impl<recursive_timed_mutex>
{
public:
typedef __native_type* native_handle_type;
recursive_timed_mutex() = default;
~recursive_timed_mutex() = default;
recursive_timed_mutex(const recursive_timed_mutex&) = delete;
recursive_timed_mutex& operator=(const recursive_timed_mutex&) = delete;
void
lock()
{
int __e = __gthread_recursive_mutex_lock(&_M_mutex);
// EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
if (__e)
__throw_system_error(__e);
}
_GLIBCXX_NODISCARD
bool
try_lock() noexcept
{
// XXX EINVAL, EAGAIN, EBUSY
return !__gthread_recursive_mutex_trylock(&_M_mutex);
}
template <class _Rep, class _Period>
_GLIBCXX_NODISCARD
bool
try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
{ return _M_try_lock_for(__rtime); }
template <class _Clock, class _Duration>
_GLIBCXX_NODISCARD
bool
try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
{ return _M_try_lock_until(__atime); }
void
unlock()
{
// XXX EINVAL, EAGAIN, EBUSY
__gthread_recursive_mutex_unlock(&_M_mutex);
}
native_handle_type
native_handle() noexcept
{ return &_M_mutex; }
private:
friend class __timed_mutex_impl<recursive_timed_mutex>;
bool
_M_timedlock(const __gthread_time_t& __ts)
{ return !__gthread_recursive_mutex_timedlock(&_M_mutex, &__ts); }
#ifdef _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
bool
_M_clocklock(clockid_t __clockid, const __gthread_time_t& __ts)
{ return !pthread_mutex_clocklock(&_M_mutex, __clockid, &__ts); }
#endif
};
#else // !_GTHREAD_USE_MUTEX_TIMEDLOCK
/// timed_mutex
class timed_mutex
{
mutex _M_mut;
condition_variable _M_cv;
bool _M_locked = false;
public:
timed_mutex() = default;
~timed_mutex() { __glibcxx_assert( !_M_locked ); }
timed_mutex(const timed_mutex&) = delete;
timed_mutex& operator=(const timed_mutex&) = delete;
void
lock()
{
unique_lock<mutex> __lk(_M_mut);
_M_cv.wait(__lk, [&]{ return !_M_locked; });
_M_locked = true;
}
_GLIBCXX_NODISCARD
bool
try_lock()
{
lock_guard<mutex> __lk(_M_mut);
if (_M_locked)
return false;
_M_locked = true;
return true;
}
template<typename _Rep, typename _Period>
_GLIBCXX_NODISCARD
bool
try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
{
unique_lock<mutex> __lk(_M_mut);
if (!_M_cv.wait_for(__lk, __rtime, [&]{ return !_M_locked; }))
return false;
_M_locked = true;
return true;
}
template<typename _Clock, typename _Duration>
_GLIBCXX_NODISCARD
bool
try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
{
unique_lock<mutex> __lk(_M_mut);
if (!_M_cv.wait_until(__lk, __atime, [&]{ return !_M_locked; }))
return false;
_M_locked = true;
return true;
}
void
unlock()
{
lock_guard<mutex> __lk(_M_mut);
__glibcxx_assert( _M_locked );
_M_locked = false;
_M_cv.notify_one();
}
};
/// recursive_timed_mutex
class recursive_timed_mutex
{
mutex _M_mut;
condition_variable _M_cv;
thread::id _M_owner;
unsigned _M_count = 0;
// Predicate type that tests whether the current thread can lock a mutex.
struct _Can_lock
{
// Returns true if the mutex is unlocked or is locked by _M_caller.
bool
operator()() const noexcept
{ return _M_mx->_M_count == 0 || _M_mx->_M_owner == _M_caller; }
const recursive_timed_mutex* _M_mx;
thread::id _M_caller;
};
public:
recursive_timed_mutex() = default;
~recursive_timed_mutex() { __glibcxx_assert( _M_count == 0 ); }
recursive_timed_mutex(const recursive_timed_mutex&) = delete;
recursive_timed_mutex& operator=(const recursive_timed_mutex&) = delete;
void
lock()
{
auto __id = this_thread::get_id();
_Can_lock __can_lock{this, __id};
unique_lock<mutex> __lk(_M_mut);
_M_cv.wait(__lk, __can_lock);
if (_M_count == -1u)
__throw_system_error(EAGAIN); // [thread.timedmutex.recursive]/3
_M_owner = __id;
++_M_count;
}
_GLIBCXX_NODISCARD
bool
try_lock()
{
auto __id = this_thread::get_id();
_Can_lock __can_lock{this, __id};
lock_guard<mutex> __lk(_M_mut);
if (!__can_lock())
return false;
if (_M_count == -1u)
return false;
_M_owner = __id;
++_M_count;
return true;
}
template<typename _Rep, typename _Period>
_GLIBCXX_NODISCARD
bool
try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
{
auto __id = this_thread::get_id();
_Can_lock __can_lock{this, __id};
unique_lock<mutex> __lk(_M_mut);
if (!_M_cv.wait_for(__lk, __rtime, __can_lock))
return false;
if (_M_count == -1u)
return false;
_M_owner = __id;
++_M_count;
return true;
}
template<typename _Clock, typename _Duration>
_GLIBCXX_NODISCARD
bool
try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
{
auto __id = this_thread::get_id();
_Can_lock __can_lock{this, __id};
unique_lock<mutex> __lk(_M_mut);
if (!_M_cv.wait_until(__lk, __atime, __can_lock))
return false;
if (_M_count == -1u)
return false;
_M_owner = __id;
++_M_count;
return true;
}
void
unlock()
{
lock_guard<mutex> __lk(_M_mut);
__glibcxx_assert( _M_owner == this_thread::get_id() );
__glibcxx_assert( _M_count > 0 );
if (--_M_count == 0)
{
_M_owner = {};
_M_cv.notify_one();
}
}
};
#endif
#endif // _GLIBCXX_HAS_GTHREADS
/// @cond undocumented
namespace __detail
{
// Lock the last lockable, after all previous ones are locked.
template<typename _Lockable>
inline int
__try_lock_impl(_Lockable& __l)
{
if (unique_lock<_Lockable> __lock{__l, try_to_lock})
{
__lock.release();
return -1;
}
else
return 0;
}
// Lock each lockable in turn.
// Use iteration if all lockables are the same type, recursion otherwise.
template<typename _L0, typename... _Lockables>
inline int
__try_lock_impl(_L0& __l0, _Lockables&... __lockables)
{
#if __cplusplus >= 201703L
if constexpr ((is_same_v<_L0, _Lockables> && ...))
{
constexpr int _Np = 1 + sizeof...(_Lockables);
unique_lock<_L0> __locks[_Np] = {
{__l0, defer_lock}, {__lockables, defer_lock}...
};
for (int __i = 0; __i < _Np; ++__i)
{
if (!__locks[__i].try_lock())
{
const int __failed = __i;
while (__i--)
__locks[__i].unlock();
return __failed;
}
}
for (auto& __l : __locks)
__l.release();
return -1;
}
else
#endif
if (unique_lock<_L0> __lock{__l0, try_to_lock})
{
int __idx = __detail::__try_lock_impl(__lockables...);
if (__idx == -1)
{
__lock.release();
return -1;
}
return __idx + 1;
}
else
return 0;
}
} // namespace __detail
/// @endcond
/** @brief Generic try_lock.
* @param __l1 Meets Lockable requirements (try_lock() may throw).
* @param __l2 Meets Lockable requirements (try_lock() may throw).
* @param __l3 Meets Lockable requirements (try_lock() may throw).
* @return Returns -1 if all try_lock() calls return true. Otherwise returns
* a 0-based index corresponding to the argument that returned false.
* @post Either all arguments are locked, or none will be.
*
* Sequentially calls try_lock() on each argument.
*/
template<typename _L1, typename _L2, typename... _L3>
_GLIBCXX_NODISCARD
inline int
try_lock(_L1& __l1, _L2& __l2, _L3&... __l3)
{
return __detail::__try_lock_impl(__l1, __l2, __l3...);
}
/// @cond undocumented
namespace __detail
{
// This function can recurse up to N levels deep, for N = 1+sizeof...(L1).
// On each recursion the lockables are rotated left one position,
// e.g. depth 0: l0, l1, l2; depth 1: l1, l2, l0; depth 2: l2, l0, l1.
// When a call to l_i.try_lock() fails it recurses/returns to depth=i
// so that l_i is the first argument, and then blocks until l_i is locked.
template<typename _L0, typename... _L1>
void
__lock_impl(int& __i, int __depth, _L0& __l0, _L1&... __l1)
{
while (__i >= __depth)
{
if (__i == __depth)
{
int __failed = 1; // index that couldn't be locked
{
unique_lock<_L0> __first(__l0);
__failed += __detail::__try_lock_impl(__l1...);
if (!__failed)
{
__i = -1; // finished
__first.release();
return;
}
}
#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
__gthread_yield();
#endif
constexpr auto __n = 1 + sizeof...(_L1);
__i = (__depth + __failed) % __n;
}
else // rotate left until l_i is first.
__detail::__lock_impl(__i, __depth + 1, __l1..., __l0);
}
}
} // namespace __detail
/// @endcond
/** @brief Generic lock.
* @param __l1 Meets Lockable requirements (try_lock() may throw).
* @param __l2 Meets Lockable requirements (try_lock() may throw).
* @param __l3 Meets Lockable requirements (try_lock() may throw).
* @throw An exception thrown by an argument's lock() or try_lock() member.
* @post All arguments are locked.
*
* All arguments are locked via a sequence of calls to lock(), try_lock()
* and unlock(). If this function exits via an exception any locks that
* were obtained will be released.
*/
template<typename _L1, typename _L2, typename... _L3>
void
lock(_L1& __l1, _L2& __l2, _L3&... __l3)
{
#if __cplusplus >= 201703L
if constexpr (is_same_v<_L1, _L2> && (is_same_v<_L1, _L3> && ...))
{
constexpr int _Np = 2 + sizeof...(_L3);
unique_lock<_L1> __locks[] = {
{__l1, defer_lock}, {__l2, defer_lock}, {__l3, defer_lock}...
};
int __first = 0;
do {
__locks[__first].lock();
for (int __j = 1; __j < _Np; ++__j)
{
const int __idx = (__first + __j) % _Np;
if (!__locks[__idx].try_lock())
{
for (int __k = __j; __k != 0; --__k)
__locks[(__first + __k - 1) % _Np].unlock();
__first = __idx;
break;
}
}
} while (!__locks[__first].owns_lock());
for (auto& __l : __locks)
__l.release();
}
else
#endif
{
int __i = 0;
__detail::__lock_impl(__i, 0, __l1, __l2, __l3...);
}
}
#if __cplusplus >= 201703L
#define __cpp_lib_scoped_lock 201703L
/** @brief A scoped lock type for multiple lockable objects.
*
* A scoped_lock controls mutex ownership within a scope, releasing
* ownership in the destructor.
*
* @headerfile mutex
* @since C++17
*/
template<typename... _MutexTypes>
class scoped_lock
{
public:
explicit scoped_lock(_MutexTypes&... __m) : _M_devices(std::tie(__m...))
{ std::lock(__m...); }
explicit scoped_lock(adopt_lock_t, _MutexTypes&... __m) noexcept
: _M_devices(std::tie(__m...))
{ } // calling thread owns mutex
~scoped_lock()
{ std::apply([](auto&... __m) { (__m.unlock(), ...); }, _M_devices); }
scoped_lock(const scoped_lock&) = delete;
scoped_lock& operator=(const scoped_lock&) = delete;
private:
tuple<_MutexTypes&...> _M_devices;
};
template<>
class scoped_lock<>
{
public:
explicit scoped_lock() = default;
explicit scoped_lock(adopt_lock_t) noexcept { }
~scoped_lock() = default;
scoped_lock(const scoped_lock&) = delete;
scoped_lock& operator=(const scoped_lock&) = delete;
};
template<typename _Mutex>
class scoped_lock<_Mutex>
{
public:
using mutex_type = _Mutex;
explicit scoped_lock(mutex_type& __m) : _M_device(__m)
{ _M_device.lock(); }
explicit scoped_lock(adopt_lock_t, mutex_type& __m) noexcept
: _M_device(__m)
{ } // calling thread owns mutex
~scoped_lock()
{ _M_device.unlock(); }
scoped_lock(const scoped_lock&) = delete;
scoped_lock& operator=(const scoped_lock&) = delete;
private:
mutex_type& _M_device;
};
#endif // C++17
#ifdef _GLIBCXX_HAS_GTHREADS
/// Flag type used by std::call_once
struct once_flag
{
constexpr once_flag() noexcept = default;
/// Deleted copy constructor
once_flag(const once_flag&) = delete;
/// Deleted assignment operator
once_flag& operator=(const once_flag&) = delete;
private:
// For gthreads targets a pthread_once_t is used with pthread_once, but
// for most targets this doesn't work correctly for exceptional executions.
__gthread_once_t _M_once = __GTHREAD_ONCE_INIT;
struct _Prepare_execution;
template<typename _Callable, typename... _Args>
friend void
call_once(once_flag& __once, _Callable&& __f, _Args&&... __args);
};
/// @cond undocumented
# ifdef _GLIBCXX_HAVE_TLS
// If TLS is available use thread-local state for the type-erased callable
// that is being run by std::call_once in the current thread.
extern __thread void* __once_callable;
extern __thread void (*__once_call)();
// RAII type to set up state for pthread_once call.
struct once_flag::_Prepare_execution
{
template<typename _Callable>
explicit
_Prepare_execution(_Callable& __c)
{
// Store address in thread-local pointer:
__once_callable = std::__addressof(__c);
// Trampoline function to invoke the closure via thread-local pointer:
__once_call = [] { (*static_cast<_Callable*>(__once_callable))(); };
}
~_Prepare_execution()
{
// PR libstdc++/82481
__once_callable = nullptr;
__once_call = nullptr;
}
_Prepare_execution(const _Prepare_execution&) = delete;
_Prepare_execution& operator=(const _Prepare_execution&) = delete;
};
# else
// Without TLS use a global std::mutex and store the callable in a
// global std::function.
extern function<void()> __once_functor;
extern void
__set_once_functor_lock_ptr(unique_lock<mutex>*);
extern mutex&
__get_once_mutex();
// RAII type to set up state for pthread_once call.
struct once_flag::_Prepare_execution
{
template<typename _Callable>
explicit
_Prepare_execution(_Callable& __c)
{
// Store the callable in the global std::function
__once_functor = __c;
__set_once_functor_lock_ptr(&_M_functor_lock);
}
~_Prepare_execution()
{
if (_M_functor_lock)
__set_once_functor_lock_ptr(nullptr);
}
private:
// XXX This deadlocks if used recursively (PR 97949)
unique_lock<mutex> _M_functor_lock{__get_once_mutex()};
_Prepare_execution(const _Prepare_execution&) = delete;
_Prepare_execution& operator=(const _Prepare_execution&) = delete;
};
# endif
/// @endcond
// This function is passed to pthread_once by std::call_once.
// It runs __once_call() or __once_functor().
extern "C" void __once_proxy(void);
/// Invoke a callable and synchronize with other calls using the same flag
template<typename _Callable, typename... _Args>
void
call_once(once_flag& __once, _Callable&& __f, _Args&&... __args)
{
// Closure type that runs the function
auto __callable = [&] {
std::__invoke(std::forward<_Callable>(__f),
std::forward<_Args>(__args)...);
};
once_flag::_Prepare_execution __exec(__callable);
// XXX pthread_once does not reset the flag if an exception is thrown.
if (int __e = __gthread_once(&__once._M_once, &__once_proxy))
__throw_system_error(__e);
}
#else // _GLIBCXX_HAS_GTHREADS
/// Flag type used by std::call_once
struct once_flag
{
constexpr once_flag() noexcept = default;
/// Deleted copy constructor
once_flag(const once_flag&) = delete;
/// Deleted assignment operator
once_flag& operator=(const once_flag&) = delete;
private:
// There are two different std::once_flag interfaces, abstracting four
// different implementations.
// The single-threaded interface uses the _M_activate() and _M_finish(bool)
// functions, which start and finish an active execution respectively.
// See [thread.once.callonce] in C++11 for the definition of
// active/passive/returning/exceptional executions.
enum _Bits : int { _Init = 0, _Active = 1, _Done = 2 };
int _M_once = _Bits::_Init;
// Check to see if all executions will be passive now.
bool
_M_passive() const noexcept;
// Attempts to begin an active execution.
bool _M_activate();
// Must be called to complete an active execution.
// The argument is true if the active execution was a returning execution,
// false if it was an exceptional execution.
void _M_finish(bool __returning) noexcept;
// RAII helper to call _M_finish.
struct _Active_execution
{
explicit _Active_execution(once_flag& __flag) : _M_flag(__flag) { }
~_Active_execution() { _M_flag._M_finish(_M_returning); }
_Active_execution(const _Active_execution&) = delete;
_Active_execution& operator=(const _Active_execution&) = delete;
once_flag& _M_flag;
bool _M_returning = false;
};
template<typename _Callable, typename... _Args>
friend void
call_once(once_flag& __once, _Callable&& __f, _Args&&... __args);
};
// Inline definitions of std::once_flag members for single-threaded targets.
inline bool
once_flag::_M_passive() const noexcept
{ return _M_once == _Bits::_Done; }
inline bool
once_flag::_M_activate()
{
if (_M_once == _Bits::_Init) [[__likely__]]
{
_M_once = _Bits::_Active;
return true;
}
else if (_M_passive()) // Caller should have checked this already.
return false;
else
__throw_system_error(EDEADLK);
}
inline void
once_flag::_M_finish(bool __returning) noexcept
{ _M_once = __returning ? _Bits::_Done : _Bits::_Init; }
/// Invoke a callable and synchronize with other calls using the same flag
template<typename _Callable, typename... _Args>
inline void
call_once(once_flag& __once, _Callable&& __f, _Args&&... __args)
{
if (__once._M_passive())
return;
else if (__once._M_activate())
{
once_flag::_Active_execution __exec(__once);
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2442. call_once() shouldn't DECAY_COPY()
std::__invoke(std::forward<_Callable>(__f),
std::forward<_Args>(__args)...);
// __f(__args...) did not throw
__exec._M_returning = true;
}
}
#endif // _GLIBCXX_HAS_GTHREADS
/// @} group mutexes
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // C++11
#endif // _GLIBCXX_MUTEX