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