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once_atomic.cpp
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91 lines (80 loc) · 2.79 KB
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// (C) Copyright 2013 Andrey Semashev
// (C) Copyright 2013 Vicente J. Botet Escriba
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//#define __STDC_CONSTANT_MACROS
#include <boost/thread/detail/config.hpp>
#include <boost/thread/once.hpp>
#include <boost/thread/pthread/pthread_helpers.hpp>
#include <boost/thread/pthread/pthread_mutex_scoped_lock.hpp>
#include <boost/assert.hpp>
#include <boost/static_assert.hpp>
#include <boost/atomic.hpp>
#include <boost/memory_order.hpp>
#include <pthread.h>
namespace boost
{
namespace thread_detail
{
enum flag_states
{
uninitialized, in_progress, initialized
};
#ifndef BOOST_THREAD_PROVIDES_ONCE_CXX11
BOOST_STATIC_ASSERT_MSG(sizeof(atomic_int_type) == sizeof(atomic_type), "Boost.Thread: unsupported platform");
#endif
static pthread_mutex_t once_mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t once_cv = PTHREAD_COND_INITIALIZER;
BOOST_THREAD_DECL bool enter_once_region(once_flag& flag) BOOST_NOEXCEPT
{
atomic_type& f = get_atomic_storage(flag);
if (f.load(memory_order_acquire) != initialized)
{
pthread::pthread_mutex_scoped_lock lk(&once_mutex);
if (f.load(memory_order_acquire) != initialized)
{
for (;;)
{
atomic_int_type expected = uninitialized;
if (f.compare_exchange_strong(expected, in_progress, memory_order_acq_rel, memory_order_acquire))
{
// We have set the flag to in_progress
return true;
}
else if (expected == initialized)
{
// Another thread managed to complete the initialization
return false;
}
else
{
// Wait until the initialization is complete
//pthread::pthread_mutex_scoped_lock lk(&once_mutex);
BOOST_VERIFY(!posix::pthread_cond_wait(&once_cv, &once_mutex));
}
}
}
}
return false;
}
BOOST_THREAD_DECL void commit_once_region(once_flag& flag) BOOST_NOEXCEPT
{
atomic_type& f = get_atomic_storage(flag);
{
pthread::pthread_mutex_scoped_lock lk(&once_mutex);
f.store(initialized, memory_order_release);
}
BOOST_VERIFY(!posix::pthread_cond_broadcast(&once_cv));
}
BOOST_THREAD_DECL void rollback_once_region(once_flag& flag) BOOST_NOEXCEPT
{
atomic_type& f = get_atomic_storage(flag);
{
pthread::pthread_mutex_scoped_lock lk(&once_mutex);
f.store(uninitialized, memory_order_release);
}
BOOST_VERIFY(!posix::pthread_cond_broadcast(&once_cv));
}
} // namespace thread_detail
} // namespace boost