Boost C++ Libraries

boost/smart_ptr/detail/spinlock_gcc_atomic.hpp

#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED
#define BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED

// MS compatible compilers support #pragma once

#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif

// Copyright 2008, 2020 Peter Dimov
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt

#include <boost/smart_ptr/detail/yield_k.hpp>

#if defined(BOOST_SP_REPORT_IMPLEMENTATION)

#include <boost/config/pragma_message.hpp>
BOOST_PRAGMA_MESSAGE("Using __atomic spinlock")

#endif

namespace boost
{

namespace detail
{

class spinlock
{
public:

    // `bool` alignment is required for Apple PPC32
    // https://github.com/boostorg/smart_ptr/issues/105
    // https://github.com/PurpleI2P/i2pd/issues/1726
    // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107590

    union
    {
        unsigned char v_;
        bool align_;
    };

public:

    bool try_lock()
    {
        return __atomic_test_and_set( &v_, __ATOMIC_ACQUIRE ) == 0;
    }

    void lock()
    {
        for( unsigned k = 0; !try_lock(); ++k )
        {
            boost::detail::yield( k );
        }
    }

    void unlock()
    {
        __atomic_clear( &v_, __ATOMIC_RELEASE );
    }

public:

    class scoped_lock
    {
    private:

        spinlock & sp_;

        scoped_lock( scoped_lock const & );
        scoped_lock & operator=( scoped_lock const & );

    public:

        explicit scoped_lock( spinlock & sp ): sp_( sp )
        {
            sp.lock();
        }

        ~scoped_lock()
        {
            sp_.unlock();
        }
    };
};

} // namespace detail
} // namespace boost

#define BOOST_DETAIL_SPINLOCK_INIT {{0}}

#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED