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
19 namespace absl {
20 ABSL_NAMESPACE_BEGIN
21
22 // Return whether int *arg is zero.
IsZero(void * arg)23 static bool IsZero(void *arg) {
24 return 0 == *reinterpret_cast<int *>(arg);
25 }
26
DecrementCount()27 bool BlockingCounter::DecrementCount() {
28 MutexLock l(&lock_);
29 count_--;
30 if (count_ < 0) {
31 ABSL_RAW_LOG(
32 FATAL,
33 "BlockingCounter::DecrementCount() called too many times. count=%d",
34 count_);
35 }
36 return count_ == 0;
37 }
38
Wait()39 void BlockingCounter::Wait() {
40 MutexLock l(&this->lock_);
41 ABSL_RAW_CHECK(count_ >= 0, "BlockingCounter underflow");
42
43 // only one thread may call Wait(). To support more than one thread,
44 // implement a counter num_to_exit, like in the Barrier class.
45 ABSL_RAW_CHECK(num_waiting_ == 0, "multiple threads called Wait()");
46 num_waiting_++;
47
48 this->lock_.Await(Condition(IsZero, &this->count_));
49
50 // At this point, We know that all threads executing DecrementCount have
51 // released the lock, and so will not touch this object again.
52 // Therefore, the thread calling this method is free to delete the object
53 // after we return from this method.
54 }
55
56 ABSL_NAMESPACE_END
57 } // namespace absl
58