0d5ce2797e
-- 20405fc394419d434d3ea09b2e62e4edcb282421 by Christian Blichmann <cblichmann@google.com>: Include `status` subdirectory in main `CMakeLists.txt` PiperOrigin-RevId: 297125966 -- 101087af9689612bdda679ee0869e5cde4472244 by Matt Kulukundis <kfm@google.com>: Fix typo PiperOrigin-RevId: 296991360 -- 55ff5bc6970d46214c0459d3a7a23973c7dc69b9 by Andy Getzendanner <durandal@google.com>: Extract logging's ErrnoSaver to absl::base_internal and use it in a couple other places. PiperOrigin-RevId: 296969168 -- b7cd7550297d53766576f751436617200c65831b by Abseil Team <absl-team@google.com>: Internal change PiperOrigin-RevId: 296951474 -- 8c04c73fc53f9a09c3e2400812b931157f35fe07 by Andy Soffer <asoffer@google.com>: Auto-generate list of files in the DLL, and add new build targets to the DLL. PiperOrigin-RevId: 296932061 -- 2f77829e196094f1addefd8ac2ac9e398c5b6100 by Andy Soffer <asoffer@google.com>: Fix bug introduced by DLL where we couldn't build shared libraries on non-windows platforms. Fixes #623 PiperOrigin-RevId: 296919347 -- b768163dbbff0c561b9dff0218a699e5e4fd33f3 by Abseil Team <absl-team@google.com>: typo: microprosessor PiperOrigin-RevId: 296904933 -- b185da0dac44c91855373f0723df9242cbfb3db3 by Matthew Brown <matthewbr@google.com>: Internal cleanup PiperOrigin-RevId: 296509711 GitOrigin-RevId: 20405fc394419d434d3ea09b2e62e4edcb282421 Change-Id: I55c8eba6f353ceb337455ae144ab743ea21edbef
66 lines
2.2 KiB
C++
66 lines
2.2 KiB
C++
// 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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