92 lines
2.9 KiB
C++
92 lines
2.9 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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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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* http://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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*/
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#ifndef TNT_UTILS_COUNTDOWNLATCH_H
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#define TNT_UTILS_COUNTDOWNLATCH_H
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#include <stddef.h>
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// note: we use our version of mutex/condition to keep this public header STL free
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#include <utils/Condition.h>
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#include <utils/Mutex.h>
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namespace utils {
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/**
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* A count down latch is used to block one or several threads until the latch is signaled
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* a certain number of times.
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*
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* Threads entering the latch are blocked until the latch is signaled enough times.
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*
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* @see CyclicBarrier
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*/
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class CountDownLatch {
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public:
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/**
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* Creates a count down latch with a specified count. The minimum useful value is 1.
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* @param count the latch counter initial value
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*/
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explicit CountDownLatch(size_t count) noexcept;
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~CountDownLatch() = default;
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/**
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* Blocks until latch() is called \p count times.
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* @see CountDownLatch(size_t count)
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*/
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void await() noexcept;
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/**
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* Releases threads blocked in await() when called \p count times. Calling latch() more than
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* \p count times has no effect.
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* @see reset()
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*/
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void latch() noexcept;
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/**
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* Resets the count-down latch to the given value.
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*
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* @param new_count New latch count. A value of zero will immediately unblock all waiting
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* threads.
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*
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* @warning Use with caution. It's only safe to reset the latch count when you're sure
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* that no threads are waiting in await(). This can be guaranteed in various ways, for
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* instance, if you have a single thread calling await(), you could call reset() from that
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* thread, or you could use a CyclicBarrier to make sure all threads using the CountDownLatch
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* are at a known place (i.e.: not in await()) when reset() is called.
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*/
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void reset(size_t new_count) noexcept;
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/**
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* @return the number of times latch() has been called since construction or reset.
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* @see reset(), CountDownLatch(size_t count)
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*/
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size_t getCount() const noexcept;
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CountDownLatch() = delete;
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CountDownLatch(const CountDownLatch&) = delete;
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CountDownLatch& operator=(const CountDownLatch&) = delete;
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private:
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uint32_t m_initial_count;
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uint32_t m_remaining_count;
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mutable Mutex m_lock;
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mutable Condition m_cv;
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};
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} // namespace utils
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#endif // TNT_UTILS_COUNTDOWNLATCH_H
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