64 lines
1.9 KiB
C++
64 lines
1.9 KiB
C++
// Copyright 2023 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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#ifndef ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_
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#define ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_
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#include <atomic>
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#include <cstdint>
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#include "absl/base/config.h"
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#include "absl/synchronization/internal/kernel_timeout.h"
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#include "absl/synchronization/internal/futex.h"
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#include "absl/synchronization/internal/waiter_base.h"
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#ifdef ABSL_INTERNAL_HAVE_FUTEX
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace synchronization_internal {
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#define ABSL_INTERNAL_HAVE_FUTEX_WAITER 1
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class FutexWaiter : public WaiterCrtp<FutexWaiter> {
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public:
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FutexWaiter() : futex_(0) {}
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bool Wait(KernelTimeout t);
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void Post();
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void Poke();
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static constexpr char kName[] = "FutexWaiter";
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private:
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// Atomically check that `*v == val`, and if it is, then sleep until the
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// timeout `t` has been reached, or until woken by `Wake()`.
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static int WaitUntil(std::atomic<int32_t>* v, int32_t val,
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KernelTimeout t);
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// Futexes are defined by specification to be 32-bits.
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// Thus std::atomic<int32_t> must be just an int32_t with lockfree methods.
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std::atomic<int32_t> futex_;
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static_assert(sizeof(int32_t) == sizeof(futex_), "Wrong size for futex");
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};
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} // namespace synchronization_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_INTERNAL_HAVE_FUTEX
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#endif // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_WAITER_H_
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