// Copyright (C) 2007 Anthony Williams
//
//  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/once.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
};

typedef boost::atomic< unsigned int > atomic_type
#if defined(__GNUC__)
    __attribute__((may_alias))
#endif
;
BOOST_STATIC_ASSERT_MSG(sizeof(once_flag) >= sizeof(atomic_type), "Boost.Thread: unsupported platform");

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 = reinterpret_cast< atomic_type& >(flag.storage);
    if (f.load(memory_order_acquire) != initialized)
    {
        while (true)
        {
            unsigned int 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(!pthread_cond_wait(&once_cv, &once_mutex));
            }
        }
    }
    else
        return false;
}

BOOST_THREAD_DECL void commit_once_region(once_flag& flag) BOOST_NOEXCEPT
{
    atomic_type& f = reinterpret_cast< atomic_type& >(flag.storage);
    pthread::pthread_mutex_scoped_lock lk(&once_mutex);
    f.store(initialized, memory_order_release);
    BOOST_VERIFY(!pthread_cond_broadcast(&once_cv));
}

BOOST_THREAD_DECL void rollback_once_region(once_flag& flag) BOOST_NOEXCEPT
{
    atomic_type& f = reinterpret_cast< atomic_type& >(flag.storage);
    pthread::pthread_mutex_scoped_lock lk(&once_mutex);
    f.store(uninitialized, memory_order_release);
    BOOST_VERIFY(!pthread_cond_broadcast(&once_cv));
}

} // namespace thread_detail

} // namespace boost