chromium/third_party/abseil-cpp/absl/synchronization/internal/futex.h

// Copyright 2020 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_
#define ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_

#include "absl/base/config.h"

#ifndef _WIN32
#include <sys/time.h>
#include <unistd.h>
#endif

#ifdef __linux__
#include <linux/futex.h>
#include <sys/syscall.h>
#endif

#include <errno.h>
#include <stdio.h>
#include <time.h>

#include <atomic>
#include <cstdint>
#include <limits>

#include "absl/base/optimization.h"
#include "absl/synchronization/internal/kernel_timeout.h"

#ifdef ABSL_INTERNAL_HAVE_FUTEX
#error ABSL_INTERNAL_HAVE_FUTEX may not be set on the command line
#elif defined(__BIONIC__)
// Bionic supports all the futex operations we need even when some of the futex
// definitions are missing.
#define ABSL_INTERNAL_HAVE_FUTEX
#elif defined(__linux__) && defined(FUTEX_CLOCK_REALTIME)
// FUTEX_CLOCK_REALTIME requires Linux >= 2.6.28.
#define ABSL_INTERNAL_HAVE_FUTEX
#endif

#ifdef ABSL_INTERNAL_HAVE_FUTEX

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace synchronization_internal {

// Some Android headers are missing these definitions even though they
// support these futex operations.
#ifdef __BIONIC__
#ifndef SYS_futex
#define SYS_futex …
#endif
#ifndef FUTEX_WAIT_BITSET
#define FUTEX_WAIT_BITSET …
#endif
#ifndef FUTEX_PRIVATE_FLAG
#define FUTEX_PRIVATE_FLAG …
#endif
#ifndef FUTEX_CLOCK_REALTIME
#define FUTEX_CLOCK_REALTIME …
#endif
#ifndef FUTEX_BITSET_MATCH_ANY
#define FUTEX_BITSET_MATCH_ANY …
#endif
#endif

#if defined(__NR_futex_time64) && !defined(SYS_futex_time64)
#define SYS_futex_time64 …
#endif

#if defined(SYS_futex_time64) && !defined(SYS_futex)
#define SYS_futex …
using FutexTimespec = struct timespec;
#else
// Some libc implementations have switched to an unconditional 64-bit `time_t`
// definition. This means that `struct timespec` may not match the layout
// expected by the kernel ABI on 32-bit platforms. So we define the
// FutexTimespec that matches the kernel timespec definition. It should be safe
// to use this struct for 64-bit userspace builds too, since it will use another
// SYS_futex kernel call with 64-bit tv_sec inside timespec.
struct FutexTimespec { … };
#endif

class FutexImpl { … };

class Futex : public FutexImpl { … };

}  // namespace synchronization_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_INTERNAL_HAVE_FUTEX

#endif  // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_