1// Copyright 2017 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// This file is a no-op if the required LowLevelAlloc support is missing.
16#include "absl/base/internal/low_level_alloc.h"
17#ifndef ABSL_LOW_LEVEL_ALLOC_MISSING
18
19#include "absl/synchronization/internal/per_thread_sem.h"
20
21#include <atomic>
22
23#include "absl/base/attributes.h"
24#include "absl/base/internal/thread_identity.h"
25#include "absl/synchronization/internal/waiter.h"
26
27namespace absl {
28namespace synchronization_internal {
29
30void PerThreadSem::SetThreadBlockedCounter(std::atomic<int> *counter) {
31 base_internal::ThreadIdentity *identity;
32 identity = GetOrCreateCurrentThreadIdentity();
33 identity->blocked_count_ptr = counter;
34}
35
36std::atomic<int> *PerThreadSem::GetThreadBlockedCounter() {
37 base_internal::ThreadIdentity *identity;
38 identity = GetOrCreateCurrentThreadIdentity();
39 return identity->blocked_count_ptr;
40}
41
42void PerThreadSem::Init(base_internal::ThreadIdentity *identity) {
43 Waiter::GetWaiter(identity)->Init();
44 identity->ticker.store(0, std::memory_order_relaxed);
45 identity->wait_start.store(0, std::memory_order_relaxed);
46 identity->is_idle.store(false, std::memory_order_relaxed);
47}
48
49void PerThreadSem::Tick(base_internal::ThreadIdentity *identity) {
50 const int ticker =
51 identity->ticker.fetch_add(1, std::memory_order_relaxed) + 1;
52 const int wait_start = identity->wait_start.load(std::memory_order_relaxed);
53 const bool is_idle = identity->is_idle.load(std::memory_order_relaxed);
54 if (wait_start && (ticker - wait_start > Waiter::kIdlePeriods) && !is_idle) {
55 // Wakeup the waiting thread since it is time for it to become idle.
56 Waiter::GetWaiter(identity)->Poke();
57 }
58}
59
60} // namespace synchronization_internal
61} // namespace absl
62
63extern "C" {
64
65ABSL_ATTRIBUTE_WEAK void AbslInternalPerThreadSemPost(
66 absl::base_internal::ThreadIdentity *identity) {
67 absl::synchronization_internal::Waiter::GetWaiter(identity)->Post();
68}
69
70ABSL_ATTRIBUTE_WEAK bool AbslInternalPerThreadSemWait(
71 absl::synchronization_internal::KernelTimeout t) {
72 bool timeout = false;
73 absl::base_internal::ThreadIdentity *identity;
74 identity = absl::synchronization_internal::GetOrCreateCurrentThreadIdentity();
75
76 // Ensure wait_start != 0.
77 int ticker = identity->ticker.load(std::memory_order_relaxed);
78 identity->wait_start.store(ticker ? ticker : 1, std::memory_order_relaxed);
79 identity->is_idle.store(false, std::memory_order_relaxed);
80
81 if (identity->blocked_count_ptr != nullptr) {
82 // Increment count of threads blocked in a given thread pool.
83 identity->blocked_count_ptr->fetch_add(1, std::memory_order_relaxed);
84 }
85
86 timeout =
87 !absl::synchronization_internal::Waiter::GetWaiter(identity)->Wait(t);
88
89 if (identity->blocked_count_ptr != nullptr) {
90 identity->blocked_count_ptr->fetch_sub(1, std::memory_order_relaxed);
91 }
92
93 identity->is_idle.store(false, std::memory_order_relaxed);
94 identity->wait_start.store(0, std::memory_order_relaxed);
95 return !timeout;
96}
97
98} // extern "C"
99
100#endif // ABSL_LOW_LEVEL_ALLOC_MISSING
101