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Diffstat (limited to 'absl/synchronization/internal/futex_waiter.h')
-rw-r--r-- | absl/synchronization/internal/futex_waiter.h | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/absl/synchronization/internal/futex_waiter.h b/absl/synchronization/internal/futex_waiter.h new file mode 100644 index 00000000..11dfa93b --- /dev/null +++ b/absl/synchronization/internal/futex_waiter.h @@ -0,0 +1,63 @@ +// Copyright 2023 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_WAITER_H_ +#define ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_ + +#include <atomic> +#include <cstdint> + +#include "absl/base/config.h" +#include "absl/synchronization/internal/kernel_timeout.h" +#include "absl/synchronization/internal/futex.h" +#include "absl/synchronization/internal/waiter_base.h" + +#ifdef ABSL_INTERNAL_HAVE_FUTEX + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace synchronization_internal { + +#define ABSL_INTERNAL_HAVE_FUTEX_WAITER 1 + +class FutexWaiter : public WaiterCrtp<FutexWaiter> { + public: + FutexWaiter() : futex_(0) {} + + bool Wait(KernelTimeout t); + void Post(); + void Poke(); + + static constexpr char kName[] = "FutexWaiter"; + + private: + // Atomically check that `*v == val`, and if it is, then sleep until the + // timeout `t` has been reached, or until woken by `Wake()`. + static int WaitUntil(std::atomic<int32_t>* v, int32_t val, + KernelTimeout t); + + // Futexes are defined by specification to be 32-bits. + // Thus std::atomic<int32_t> must be just an int32_t with lockfree methods. + std::atomic<int32_t> futex_; + static_assert(sizeof(int32_t) == sizeof(futex_), "Wrong size for futex"); +}; + +} // namespace synchronization_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_INTERNAL_HAVE_FUTEX + +#endif // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_ |