futex_waiter.h (1972B)
1 // Copyright 2023 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 16 #ifndef ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_ 17 #define ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_ 18 19 #include <atomic> 20 #include <cstdint> 21 22 #include "absl/base/config.h" 23 #include "absl/synchronization/internal/kernel_timeout.h" 24 #include "absl/synchronization/internal/futex.h" 25 #include "absl/synchronization/internal/waiter_base.h" 26 27 #ifdef ABSL_INTERNAL_HAVE_FUTEX 28 29 namespace absl { 30 ABSL_NAMESPACE_BEGIN 31 namespace synchronization_internal { 32 33 #define ABSL_INTERNAL_HAVE_FUTEX_WAITER 1 34 35 class FutexWaiter : public WaiterCrtp<FutexWaiter> { 36 public: 37 FutexWaiter() : futex_(0) {} 38 39 bool Wait(KernelTimeout t); 40 void Post(); 41 void Poke(); 42 43 static constexpr char kName[] = "FutexWaiter"; 44 45 private: 46 // Atomically check that `*v == val`, and if it is, then sleep until the 47 // timeout `t` has been reached, or until woken by `Wake()`. 48 static int WaitUntil(std::atomic<int32_t>* v, int32_t val, 49 KernelTimeout t); 50 51 // Futexes are defined by specification to be 32-bits. 52 // Thus std::atomic<int32_t> must be just an int32_t with lockfree methods. 53 std::atomic<int32_t> futex_; 54 static_assert(sizeof(int32_t) == sizeof(futex_), "Wrong size for futex"); 55 }; 56 57 } // namespace synchronization_internal 58 ABSL_NAMESPACE_END 59 } // namespace absl 60 61 #endif // ABSL_INTERNAL_HAVE_FUTEX 62 63 #endif // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_