| // 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 loop, |
| absl::base_internal::SchedulingMode) { |
| absl::base_internal::ErrnoSaver errno_saver; |
| struct timespec tm; |
| tm.tv_sec = 0; |
| tm.tv_nsec = absl::base_internal::SpinLockSuggestedDelayNS(loop); |
| syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, &tm); |
| } |
| |
| 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" |