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/*
* Copyright 2019 The libgav1 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
*
* http://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.
*/
#ifndef LIBGAV1_SRC_UTILS_BLOCKING_COUNTER_H_
#define LIBGAV1_SRC_UTILS_BLOCKING_COUNTER_H_
#include <cassert>
#include <condition_variable> // NOLINT (unapproved c++11 header)
#include <mutex> // NOLINT (unapproved c++11 header)
#include "src/utils/compiler_attributes.h"
namespace libgav1 {
// Implementation of a Blocking Counter that is used for the "fork-join"
// use case. Typical usage would be as follows:
// BlockingCounter counter(num_jobs);
// - spawn the jobs.
// - call counter.Wait() on the master thread.
// - worker threads will call counter.Decrement().
// - master thread will return from counter.Wait() when all workers are
// complete.
template <bool has_failure_status>
class BlockingCounterImpl {
public:
explicit BlockingCounterImpl(int initial_count)
: count_(initial_count), job_failed_(false) {}
// Increment the counter by |count|. This must be called before Wait() is
// called. This must be called from the same thread that will call Wait().
void IncrementBy(int count) {
assert(count >= 0);
std::unique_lock<std::mutex> lock(mutex_);
count_ += count;
}
// Decrement the counter by 1. This function can be called only when
// |has_failure_status| is false (i.e.) when this class is being used with the
// |BlockingCounter| alias.
void Decrement() {
static_assert(!has_failure_status, "");
std::unique_lock<std::mutex> lock(mutex_);
if (--count_ == 0) {
condition_.notify_one();
}
}
// Decrement the counter by 1. This function can be called only when
// |has_failure_status| is true (i.e.) when this class is being used with the
// |BlockingCounterWithStatus| alias. |job_succeeded| is used to update the
// state of |job_failed_|.
void Decrement(bool job_succeeded) {
static_assert(has_failure_status, "");
std::unique_lock<std::mutex> lock(mutex_);
job_failed_ |= !job_succeeded;
if (--count_ == 0) {
condition_.notify_one();
}
}
// Block until the counter becomes 0. This function can be called only once
// per object. If |has_failure_status| is true, true is returned if all the
// jobs succeeded and false is returned if any of the jobs failed. If
// |has_failure_status| is false, this function always returns true.
bool Wait() {
std::unique_lock<std::mutex> lock(mutex_);
condition_.wait(lock, [this]() { return count_ == 0; });
// If |has_failure_status| is false, we simply return true.
return has_failure_status ? !job_failed_ : true;
}
private:
std::mutex mutex_;
std::condition_variable condition_;
int count_ LIBGAV1_GUARDED_BY(mutex_);
bool job_failed_ LIBGAV1_GUARDED_BY(mutex_);
};
using BlockingCounterWithStatus = BlockingCounterImpl<true>;
using BlockingCounter = BlockingCounterImpl<false>;
} // namespace libgav1
#endif // LIBGAV1_SRC_UTILS_BLOCKING_COUNTER_H_
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