From 4b2fbb4adba905eede6c61b4494acfdb660a3bb7 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Mon, 12 Oct 2020 10:33:47 -0700 Subject: Export of internal Abseil changes -- a5af5874c1c5cc02bd2a748d455321f82b6f2a93 by Andy Getzendanner : fix compile fails with asan and -Wredundant-decls Import of https://github.com/abseil/abseil-cpp/pull/801 PiperOrigin-RevId: 336693223 -- ed9df42ab2b742386c6692c2bed015374c919d9c by Derek Mauro : Fix integer conversion warning Fixes #814 PiperOrigin-RevId: 336651814 -- 0ab4c23884e72dce17b67c1eb520f9dbb802565d by Derek Mauro : Internal change PiperOrigin-RevId: 336585378 -- eba0e3dccd52a6e91bcff84075bef0affc650b74 by Matt Kulukundis : Add bitset operations to Futex helper. PiperOrigin-RevId: 336409368 -- 8b0709a8b4500bf5f0af4b602d76a298d81645e8 by Abseil Team : Fix code indentation in a comment. PiperOrigin-RevId: 336368167 -- bc3961c87a7e7760c10319a5b0349c279f7ae3ad by Samuel Benzaquen : Improve performance of the registry: - Reduce contention - Reduce memory usage for each flag by `6*sizeof(void*)`. - Replace one immortal allocation per-flag with a single one for all the flags - Slightly improve single-threaded performance by avoiding the std::map indirections. PiperOrigin-RevId: 336365904 -- 264ad9f28f935aad8b6b1437f8bf804fa9104346 by Abseil Team : Fix typo in comment on absl::Condition. PiperOrigin-RevId: 336311680 -- b5b808a8c75ca0df7b09eff9a423ec171d80f771 by Derek Mauro : Add missing Apache license headers PiperOrigin-RevId: 336294980 -- 89446c3a4793df8b95060385cf3e219357c3db1d by Andy Soffer : Internal changes PiperOrigin-RevId: 336287465 -- 57c8be4e294881bc79a6a44b8e4bf7ecbb19b9b9 by Matt Kulukundis : Extract Futex from an implementation detail of Wait to a private interface. PiperOrigin-RevId: 336123209 GitOrigin-RevId: a5af5874c1c5cc02bd2a748d455321f82b6f2a93 Change-Id: Ie5a0ebe28e571814e3e11d4c05ca308523ccf311 --- absl/synchronization/internal/futex.h | 139 ++++++++++++++++++++++++++++++++++ 1 file changed, 139 insertions(+) create mode 100644 absl/synchronization/internal/futex.h (limited to 'absl/synchronization/internal/futex.h') diff --git a/absl/synchronization/internal/futex.h b/absl/synchronization/internal/futex.h new file mode 100644 index 00000000..3539f491 --- /dev/null +++ b/absl/synchronization/internal/futex.h @@ -0,0 +1,139 @@ +// 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" + +#ifdef _WIN32 +#include +#else +#include +#include +#endif + +#ifdef __linux__ +#include +#include +#endif + +#include +#include +#include + +#include +#include + +#include "absl/base/optimization.h" +#include "absl/synchronization/internal/kernel_timeout.h" + +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 __NR_futex +#endif +#ifndef FUTEX_WAIT_BITSET +#define FUTEX_WAIT_BITSET 9 +#endif +#ifndef FUTEX_PRIVATE_FLAG +#define FUTEX_PRIVATE_FLAG 128 +#endif +#ifndef FUTEX_CLOCK_REALTIME +#define FUTEX_CLOCK_REALTIME 256 +#endif +#ifndef FUTEX_BITSET_MATCH_ANY +#define FUTEX_BITSET_MATCH_ANY 0xFFFFFFFF +#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 + +class FutexImpl { + public: + static int WaitUntil(std::atomic *v, int32_t val, + KernelTimeout t) { + int err = 0; + if (t.has_timeout()) { + // https://locklessinc.com/articles/futex_cheat_sheet/ + // Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET uses absolute time. + struct timespec abs_timeout = t.MakeAbsTimespec(); + // Atomically check that the futex value is still 0, and if it + // is, sleep until abs_timeout or until woken by FUTEX_WAKE. + err = syscall( + SYS_futex, reinterpret_cast(v), + FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME, val, + &abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY); + } else { + // Atomically check that the futex value is still 0, and if it + // is, sleep until woken by FUTEX_WAKE. + err = syscall(SYS_futex, reinterpret_cast(v), + FUTEX_WAIT | FUTEX_PRIVATE_FLAG, val, nullptr); + } + if (ABSL_PREDICT_FALSE(err != 0)) { + err = -errno; + } + return err; + } + + static int WaitBitsetAbsoluteTimeout(std::atomic *v, int32_t val, + int32_t bits, + const struct timespec *abstime) { + int err = syscall(SYS_futex, reinterpret_cast(v), + FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG, val, abstime, + nullptr, bits); + if (ABSL_PREDICT_FALSE(err != 0)) { + err = -errno; + } + return err; + } + + static int Wake(std::atomic *v, int32_t count) { + int err = syscall(SYS_futex, reinterpret_cast(v), + FUTEX_WAKE | FUTEX_PRIVATE_FLAG, count); + if (ABSL_PREDICT_FALSE(err < 0)) { + err = -errno; + } + return err; + } + + // FUTEX_WAKE_BITSET + static int WakeBitset(std::atomic *v, int32_t count, int32_t bits) { + int err = syscall(SYS_futex, reinterpret_cast(v), + FUTEX_WAKE_BITSET | FUTEX_PRIVATE_FLAG, count, nullptr, + nullptr, bits); + if (ABSL_PREDICT_FALSE(err < 0)) { + err = -errno; + } + return err; + } +}; + +class Futex : public FutexImpl {}; + +} // namespace synchronization_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_ -- cgit v1.2.3