Abseil Common Libraries (C++) (grcp 依赖)
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66 lines
2.2 KiB
66 lines
2.2 KiB
// Copyright 2018 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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// |
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// This file is a Linux-specific part of spinlock_wait.cc |
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#include <linux/futex.h> |
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#include <sys/syscall.h> |
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#include <unistd.h> |
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#include <atomic> |
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#include <climits> |
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#include <cstdint> |
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#include <ctime> |
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#include "absl/base/attributes.h" |
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#include "absl/base/internal/errno_saver.h" |
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// The SpinLock lockword is `std::atomic<uint32_t>`. Here we assert that |
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// `std::atomic<uint32_t>` is bitwise equivalent of the `int` expected |
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// by SYS_futex. We also assume that reads/writes done to the lockword |
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// by SYS_futex have rational semantics with regard to the |
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// std::atomic<> API. C++ provides no guarantees of these assumptions, |
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// but they are believed to hold in practice. |
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static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int), |
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"SpinLock lockword has the wrong size for a futex"); |
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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_PRIVATE_FLAG |
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#define FUTEX_PRIVATE_FLAG 128 |
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#endif |
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#endif |
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extern "C" { |
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ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay( |
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std::atomic<uint32_t> *w, uint32_t value, int loop, |
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absl::base_internal::SchedulingMode) { |
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absl::base_internal::ErrnoSaver errno_saver; |
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struct timespec tm; |
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tm.tv_sec = 0; |
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tm.tv_nsec = absl::base_internal::SpinLockSuggestedDelayNS(loop); |
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syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, &tm); |
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} |
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ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockWake(std::atomic<uint32_t> *w, |
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bool all) { |
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syscall(SYS_futex, w, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, all ? INT_MAX : 1, 0); |
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} |
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} // extern "C"
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