Boost C++ Libraries

boost/atomic/detail/futex.hpp

/*
 * 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)
 *
 * Copyright (c) 2020 Andrey Semashev
 */
/*!
 * \file   atomic/detail/futex.hpp
 *
 * This header defines wrappers around futex syscall.
 *
 * http://man7.org/linux/man-pages/man2/futex.2.html
 * https://man.openbsd.org/futex
 */

#ifndef BOOST_ATOMIC_DETAIL_FUTEX_HPP_INCLUDED_
#define BOOST_ATOMIC_DETAIL_FUTEX_HPP_INCLUDED_

#include <boost/atomic/detail/config.hpp>

#ifdef BOOST_HAS_PRAGMA_ONCE
#pragma once
#endif

#if defined(__linux__) || defined(__OpenBSD__) || defined(__NETBSD__) || defined(__NetBSD__)

#include <sys/syscall.h>

#if defined(SYS_futex)
#define BOOST_ATOMIC_DETAIL_SYS_FUTEX SYS_futex
#elif defined(SYS_futex_time64)
// On some 32-bit targets (e.g. riscv32) SYS_futex is not defined and instead SYS_futex_time64 is implemented,
// which is equivalent to SYS_futex but uses 64-bit time_t.
#define BOOST_ATOMIC_DETAIL_SYS_FUTEX SYS_futex_time64
#elif defined(__NR_futex)
// Some Android NDKs (Google NDK and older Crystax.NET NDK versions) don't define SYS_futex.
#define BOOST_ATOMIC_DETAIL_SYS_FUTEX __NR_futex
#elif defined(SYS___futex)
// NetBSD defines SYS___futex, which has slightly different parameters. Basically, it has decoupled timeout and val2 parameters:
// int __futex(int *addr1, int op, int val1, const struct timespec *timeout, int *addr2, int val2, int val3);
// https://ftp.netbsd.org/pub/NetBSD/NetBSD-current/src/sys/sys/syscall.h
// http://bxr.su/NetBSD/sys/kern/sys_futex.c
#define BOOST_ATOMIC_DETAIL_SYS_FUTEX SYS___futex
#define BOOST_ATOMIC_DETAIL_NETBSD_FUTEX
#endif

#if defined(BOOST_ATOMIC_DETAIL_SYS_FUTEX)

#include <cstddef>
#if defined(__linux__)
#include <linux/futex.h>
#else
#include <sys/futex.h>
#endif
#include <boost/atomic/detail/intptr.hpp>
#include <boost/atomic/detail/header.hpp>

#define BOOST_ATOMIC_DETAIL_HAS_FUTEX

#if defined(FUTEX_PRIVATE_FLAG)
#define BOOST_ATOMIC_DETAIL_FUTEX_PRIVATE_FLAG FUTEX_PRIVATE_FLAG
#elif defined(__ANDROID__)
// On Android, futex.h is lacking many definitions, but the actual Linux kernel supports the API in full.
#define BOOST_ATOMIC_DETAIL_FUTEX_PRIVATE_FLAG 128
#else
#define BOOST_ATOMIC_DETAIL_FUTEX_PRIVATE_FLAG 0
#endif

namespace boost {
namespace atomics {
namespace detail {

//! Invokes an operation on the futex
BOOST_FORCEINLINE int futex_invoke(void* addr1, int op, unsigned int val1, const void* timeout = NULL, void* addr2 = NULL, unsigned int val3 = 0) BOOST_NOEXCEPT
{
#if !defined(BOOST_ATOMIC_DETAIL_NETBSD_FUTEX)
    return ::syscall(BOOST_ATOMIC_DETAIL_SYS_FUTEX, addr1, op, val1, timeout, addr2, val3);
#else
    // Pass 0 in val2.
    return ::syscall(BOOST_ATOMIC_DETAIL_SYS_FUTEX, addr1, op, val1, timeout, addr2, 0u, val3);
#endif
}

//! Invokes an operation on the futex
BOOST_FORCEINLINE int futex_invoke(void* addr1, int op, unsigned int val1, unsigned int val2, void* addr2 = NULL, unsigned int val3 = 0) BOOST_NOEXCEPT
{
#if !defined(BOOST_ATOMIC_DETAIL_NETBSD_FUTEX)
    return ::syscall(BOOST_ATOMIC_DETAIL_SYS_FUTEX, addr1, op, val1, static_cast< atomics::detail::uintptr_t >(val2), addr2, val3);
#else
    // Pass NULL in timeout.
    return ::syscall(BOOST_ATOMIC_DETAIL_SYS_FUTEX, addr1, op, val1, static_cast< void* >(NULL), addr2, val2, val3);
#endif
}

//! Checks that the value \c pval is \c expected and blocks
BOOST_FORCEINLINE int futex_wait(void* pval, unsigned int expected) BOOST_NOEXCEPT
{
    return futex_invoke(pval, FUTEX_WAIT, expected);
}

//! Checks that the value \c pval is \c expected and blocks
BOOST_FORCEINLINE int futex_wait_private(void* pval, unsigned int expected) BOOST_NOEXCEPT
{
    return futex_invoke(pval, FUTEX_WAIT | BOOST_ATOMIC_DETAIL_FUTEX_PRIVATE_FLAG, expected);
}

//! Wakes the specified number of threads waiting on the futex
BOOST_FORCEINLINE int futex_signal(void* pval, unsigned int count = 1u) BOOST_NOEXCEPT
{
    return futex_invoke(pval, FUTEX_WAKE, count);
}

//! Wakes the specified number of threads waiting on the futex
BOOST_FORCEINLINE int futex_signal_private(void* pval, unsigned int count = 1u) BOOST_NOEXCEPT
{
    return futex_invoke(pval, FUTEX_WAKE | BOOST_ATOMIC_DETAIL_FUTEX_PRIVATE_FLAG, count);
}

//! Wakes all threads waiting on the futex
BOOST_FORCEINLINE int futex_broadcast(void* pval) BOOST_NOEXCEPT
{
    return futex_signal(pval, (~static_cast< unsigned int >(0u)) >> 1);
}

//! Wakes all threads waiting on the futex
BOOST_FORCEINLINE int futex_broadcast_private(void* pval) BOOST_NOEXCEPT
{
    return futex_signal_private(pval, (~static_cast< unsigned int >(0u)) >> 1);
}

//! Wakes the wake_count threads waiting on the futex pval1 and requeues up to requeue_count of the blocked threads onto another futex pval2
BOOST_FORCEINLINE int futex_requeue(void* pval1, void* pval2, unsigned int wake_count = 1u, unsigned int requeue_count = (~static_cast< unsigned int >(0u)) >> 1) BOOST_NOEXCEPT
{
    return futex_invoke(pval1, FUTEX_REQUEUE, wake_count, requeue_count, pval2);
}

//! Wakes the wake_count threads waiting on the futex pval1 and requeues up to requeue_count of the blocked threads onto another futex pval2
BOOST_FORCEINLINE int futex_requeue_private(void* pval1, void* pval2, unsigned int wake_count = 1u, unsigned int requeue_count = (~static_cast< unsigned int >(0u)) >> 1) BOOST_NOEXCEPT
{
    return futex_invoke(pval1, FUTEX_REQUEUE | BOOST_ATOMIC_DETAIL_FUTEX_PRIVATE_FLAG, wake_count, requeue_count, pval2);
}

} // namespace detail
} // namespace atomics
} // namespace boost

#include <boost/atomic/detail/footer.hpp>

#endif // defined(BOOST_ATOMIC_DETAIL_SYS_FUTEX)

#endif // defined(__linux__) || defined(__OpenBSD__) || defined(__NETBSD__) || defined(__NetBSD__)

#endif // BOOST_ATOMIC_DETAIL_FUTEX_HPP_INCLUDED_