/src/abseil-cpp/absl/synchronization/internal/futex_waiter.h
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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 | 2 | 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_ |