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/barrier.h"
16
17#include "absl/base/internal/raw_logging.h"
18#include "absl/synchronization/mutex.h"
19
20namespace absl {
21
22// Return whether int *arg is zero.
23static bool IsZero(void *arg) {
24 return 0 == *reinterpret_cast<int *>(arg);
25}
26
27bool Barrier::Block() {
28 MutexLock l(&this->lock_);
29
30 this->num_to_block_--;
31 if (this->num_to_block_ < 0) {
32 ABSL_RAW_LOG(
33 FATAL,
34 "Block() called too many times. num_to_block_=%d out of total=%d",
35 this->num_to_block_, this->num_to_exit_);
36 }
37
38 this->lock_.Await(Condition(IsZero, &this->num_to_block_));
39
40 // Determine which thread can safely delete this Barrier object
41 this->num_to_exit_--;
42 ABSL_RAW_CHECK(this->num_to_exit_ >= 0, "barrier underflow");
43
44 // If num_to_exit_ == 0 then all other threads in the barrier have
45 // exited the Wait() and have released the Mutex so this thread is
46 // free to delete the barrier.
47 return this->num_to_exit_ == 0;
48}
49
50} // namespace absl
51