1/* Copyright 2015 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7 http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#ifndef TENSORFLOW_TSL_PLATFORM_BLOCKING_COUNTER_H_
17#define TENSORFLOW_TSL_PLATFORM_BLOCKING_COUNTER_H_
18
19#include <atomic>
20
21#include "tensorflow/tsl/platform/logging.h"
22#include "tensorflow/tsl/platform/mutex.h"
23
24namespace tsl {
25
26class BlockingCounter {
27 public:
28 BlockingCounter(int initial_count)
29 : state_(initial_count << 1), notified_(false) {
30 CHECK_GE(initial_count, 0);
31 DCHECK_EQ((initial_count << 1) >> 1, initial_count);
32 }
33
34 ~BlockingCounter() {}
35
36 inline void DecrementCount() {
37 unsigned int v = state_.fetch_sub(2, std::memory_order_acq_rel) - 2;
38 if (v != 1) {
39 DCHECK_NE(((v + 2) & ~1), 0);
40 return; // either count has not dropped to 0, or waiter is not waiting
41 }
42 mutex_lock l(mu_);
43 DCHECK(!notified_);
44 notified_ = true;
45 cond_var_.notify_all();
46 }
47
48 inline void Wait() {
49 unsigned int v = state_.fetch_or(1, std::memory_order_acq_rel);
50 if ((v >> 1) == 0) return;
51 mutex_lock l(mu_);
52 while (!notified_) {
53 cond_var_.wait(l);
54 }
55 }
56 // Wait for the specified time, return false iff the count has not dropped to
57 // zero before the timeout expired.
58 inline bool WaitFor(std::chrono::milliseconds ms) {
59 unsigned int v = state_.fetch_or(1, std::memory_order_acq_rel);
60 if ((v >> 1) == 0) return true;
61 mutex_lock l(mu_);
62 while (!notified_) {
63 const std::cv_status status = cond_var_.wait_for(l, ms);
64 if (status == std::cv_status::timeout) {
65 return false;
66 }
67 }
68 return true;
69 }
70
71 private:
72 mutex mu_;
73 condition_variable cond_var_;
74 std::atomic<int> state_; // low bit is waiter flag
75 bool notified_;
76};
77
78} // namespace tsl
79
80#endif // TENSORFLOW_TSL_PLATFORM_BLOCKING_COUNTER_H_
81