// Copyright 2017 The Abseil Authors. // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // https://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. #include "absl/synchronization/blocking_counter.h" #include <atomic> #include "absl/base/internal/raw_logging.h" namespace absl { ABSL_NAMESPACE_BEGIN namespace { // Return whether int *arg is true. bool IsDone(void *arg) { return *reinterpret_cast<bool *>(arg); } } // namespace BlockingCounter::BlockingCounter(int initial_count) : count_(initial_count), num_waiting_(0), done_{initial_count == 0 ? true : false} { ABSL_RAW_CHECK(initial_count >= 0, "BlockingCounter initial_count negative"); } bool BlockingCounter::DecrementCount() { int count = count_.fetch_sub(1, std::memory_order_acq_rel) - 1; ABSL_RAW_CHECK(count >= 0, "BlockingCounter::DecrementCount() called too many times"); if (count == 0) { MutexLock l(&lock_); done_ = true; return true; } return false; } void BlockingCounter::Wait() { MutexLock l(&this->lock_); // only one thread may call Wait(). To support more than one thread, // implement a counter num_to_exit, like in the Barrier class. ABSL_RAW_CHECK(num_waiting_ == 0, "multiple threads called Wait()"); num_waiting_++; this->lock_.Await(Condition(IsDone, &this->done_)); // At this point, we know that all threads executing DecrementCount // will not touch this object again. // Therefore, the thread calling this method is free to delete the object // after we return from this method. } ABSL_NAMESPACE_END } // namespace absl