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// 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
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