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#include "absl/synchronization/blocking_counter.h"
16
17#include "absl/base/internal/raw_logging.h"
18
19namespace absl {
20
21// Return whether int *arg is zero.
22static bool IsZero(void *arg) {
23 return 0 == *reinterpret_cast<int *>(arg);
24}
25
26bool BlockingCounter::DecrementCount() {
27 MutexLock l(&lock_);
28 count_--;
29 if (count_ < 0) {
30 ABSL_RAW_LOG(
31 FATAL,
32 "BlockingCounter::DecrementCount() called too many times. count=%d",
33 count_);
34 }
35 return count_ == 0;
36}
37
38void BlockingCounter::Wait() {
39 MutexLock l(&this->lock_);
40 ABSL_RAW_CHECK(count_ >= 0, "BlockingCounter underflow");
41
42 // only one thread may call Wait(). To support more than one thread,
43 // implement a counter num_to_exit, like in the Barrier class.
44 ABSL_RAW_CHECK(num_waiting_ == 0, "multiple threads called Wait()");
45 num_waiting_++;
46
47 this->lock_.Await(Condition(IsZero, &this->count_));
48
49 // At this point, We know that all threads executing DecrementCount have
50 // released the lock, and so will not touch this object again.
51 // Therefore, the thread calling this method is free to delete the object
52 // after we return from this method.
53}
54
55} // namespace absl
56