// Copyright 2018 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.

//

// This file is a Linux-specific part of spinlock_wait.cc

#include <linux/futex.h>

#include <sys/syscall.h>

#include <unistd.h>

#include <atomic>

#include <climits>

#include <cstdint>

#include <ctime>

#include "absl/base/attributes.h"

#include "absl/base/internal/errno_saver.h"

// The SpinLock lockword is `std::atomic<uint32_t>`. Here we assert that

// `std::atomic<uint32_t>` is bitwise equivalent of the `int` expected

// by SYS_futex. We also assume that reads/writes done to the lockword

// by SYS_futex have rational semantics with regard to the

// std::atomic<> API. C++ provides no guarantees of these assumptions,

// but they are believed to hold in practice.

static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int),

              "SpinLock lockword has the wrong size for a futex");

// Some Android headers are missing these definitions even though they

// support these futex operations.

#ifdef __BIONIC__

#ifndef SYS_futex

#define SYS_futex __NR_futex

#endif

#ifndef FUTEX_PRIVATE_FLAG

#define FUTEX_PRIVATE_FLAG 128

#endif

#endif

#if defined(__NR_futex_time64) && !defined(SYS_futex_time64)

#define SYS_futex_time64 __NR_futex_time64

#endif

#if defined(SYS_futex_time64) && !defined(SYS_futex)

#define SYS_futex SYS_futex_time64

#endif

extern "C" {

ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(

    std::atomic<uint32_t> *w, uint32_t value, int,

    absl::base_internal::SchedulingMode) {

  absl::base_internal::ErrnoSaver errno_saver;

  syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, nullptr);

}

ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(

    std::atomic<uint32_t> *w, bool all) {

  syscall(SYS_futex, w, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, all ? INT_MAX : 1, 0);

}

}  // extern "C"