155 lines
4.5 KiB
C++
155 lines
4.5 KiB
C++
// Copyright 2020 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_
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#define ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_
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#include "absl/base/config.h"
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#ifdef _WIN32
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#include <windows.h>
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#else
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#include <sys/time.h>
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#include <unistd.h>
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#endif
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#ifdef __linux__
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#include <linux/futex.h>
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#include <sys/syscall.h>
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#endif
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#include <errno.h>
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#include <stdio.h>
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#include <time.h>
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#include <atomic>
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#include <cstdint>
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#include "absl/base/optimization.h"
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#include "absl/synchronization/internal/kernel_timeout.h"
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#ifdef ABSL_INTERNAL_HAVE_FUTEX
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#error ABSL_INTERNAL_HAVE_FUTEX may not be set on the command line
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#elif defined(__BIONIC__)
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// Bionic supports all the futex operations we need even when some of the futex
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// definitions are missing.
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#define ABSL_INTERNAL_HAVE_FUTEX
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#elif defined(__linux__) && defined(FUTEX_CLOCK_REALTIME)
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// FUTEX_CLOCK_REALTIME requires Linux >= 2.6.28.
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#define ABSL_INTERNAL_HAVE_FUTEX
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#endif
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#ifdef ABSL_INTERNAL_HAVE_FUTEX
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace synchronization_internal {
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// Some Android headers are missing these definitions even though they
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// support these futex operations.
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#ifdef __BIONIC__
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#ifndef SYS_futex
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#define SYS_futex __NR_futex
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#endif
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#ifndef FUTEX_WAIT_BITSET
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#define FUTEX_WAIT_BITSET 9
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#endif
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#ifndef FUTEX_PRIVATE_FLAG
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#define FUTEX_PRIVATE_FLAG 128
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#endif
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#ifndef FUTEX_CLOCK_REALTIME
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#define FUTEX_CLOCK_REALTIME 256
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#endif
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#ifndef FUTEX_BITSET_MATCH_ANY
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#define FUTEX_BITSET_MATCH_ANY 0xFFFFFFFF
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#endif
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#endif
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#if defined(__NR_futex_time64) && !defined(SYS_futex_time64)
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#define SYS_futex_time64 __NR_futex_time64
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#endif
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#if defined(SYS_futex_time64) && !defined(SYS_futex)
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#define SYS_futex SYS_futex_time64
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#endif
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class FutexImpl {
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public:
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static int WaitUntil(std::atomic<int32_t> *v, int32_t val,
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KernelTimeout t) {
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int err = 0;
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if (t.has_timeout()) {
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// https://locklessinc.com/articles/futex_cheat_sheet/
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// Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET uses absolute time.
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struct timespec abs_timeout = t.MakeAbsTimespec();
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// Atomically check that the futex value is still 0, and if it
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// is, sleep until abs_timeout or until woken by FUTEX_WAKE.
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err = syscall(
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SYS_futex, reinterpret_cast<int32_t *>(v),
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FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME, val,
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&abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY);
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} else {
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// Atomically check that the futex value is still 0, and if it
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// is, sleep until woken by FUTEX_WAKE.
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err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v),
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FUTEX_WAIT | FUTEX_PRIVATE_FLAG, val, nullptr);
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}
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if (ABSL_PREDICT_FALSE(err != 0)) {
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err = -errno;
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}
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return err;
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}
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static int WaitBitsetAbsoluteTimeout(std::atomic<int32_t> *v, int32_t val,
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int32_t bits,
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const struct timespec *abstime) {
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int err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v),
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FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG, val, abstime,
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nullptr, bits);
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if (ABSL_PREDICT_FALSE(err != 0)) {
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err = -errno;
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}
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return err;
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}
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static int Wake(std::atomic<int32_t> *v, int32_t count) {
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int err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v),
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FUTEX_WAKE | FUTEX_PRIVATE_FLAG, count);
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if (ABSL_PREDICT_FALSE(err < 0)) {
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err = -errno;
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}
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return err;
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}
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// FUTEX_WAKE_BITSET
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static int WakeBitset(std::atomic<int32_t> *v, int32_t count, int32_t bits) {
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int err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v),
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FUTEX_WAKE_BITSET | FUTEX_PRIVATE_FLAG, count, nullptr,
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nullptr, bits);
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if (ABSL_PREDICT_FALSE(err < 0)) {
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err = -errno;
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}
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return err;
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}
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};
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class Futex : public FutexImpl {};
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} // namespace synchronization_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_INTERNAL_HAVE_FUTEX
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#endif // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_
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