77 lines
2.9 KiB
C++
77 lines
2.9 KiB
C++
/*
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* Copyright (C) 2012 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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// CAUTION: THIS IS NOT A FULLY GENERAL BARRIER API.
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// It may either be used as a "latch" or single-use barrier, or it may be reused under
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// very limited conditions, e.g. if only Pass(), but not Wait() is called. Unlike a standard
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// latch API, it is possible to initialize the latch to a count of zero, repeatedly call
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// Pass() or Wait(), and only then set the count using the Increment() method. Threads at
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// a Wait() are only awoken if the count reaches zero AFTER the decrement is applied.
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// This works because, also unlike most latch APIs, there is no way to Wait() without
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// decrementing the count, and thus nobody can spuriosly wake up on the initial zero.
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#ifndef ART_RUNTIME_BARRIER_H_
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#define ART_RUNTIME_BARRIER_H_
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#include <memory>
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#include "base/mutex.h"
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namespace art {
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// TODO: Maybe give this a better name.
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class Barrier {
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public:
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explicit Barrier(int count);
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virtual ~Barrier();
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// Pass through the barrier, decrement the count but do not block.
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void Pass(Thread* self) REQUIRES(!lock_);
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// Wait on the barrier, decrement the count.
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void Wait(Thread* self) REQUIRES(!lock_);
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// The following three calls are only safe if we somehow know that no other thread both
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// - has been woken up, and
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// - has not left the Wait() or Increment() call.
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// If these calls are made in that situation, the offending thread is likely to go back
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// to sleep, resulting in a deadlock.
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// Increment the count by delta, wait on condition if count is non zero.
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void Increment(Thread* self, int delta) REQUIRES(!lock_);
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// Increment the count by delta, wait on condition if count is non zero, with a timeout. Returns
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// true if time out occurred.
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bool Increment(Thread* self, int delta, uint32_t timeout_ms) REQUIRES(!lock_);
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// Set the count to a new value. This should only be used if there is no possibility that
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// another thread is still in Wait(). See above.
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void Init(Thread* self, int count) REQUIRES(!lock_);
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int GetCount(Thread* self) REQUIRES(!lock_);
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private:
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void SetCountLocked(Thread* self, int count) REQUIRES(lock_);
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// Counter, when this reaches 0 all people blocked on the barrier are signalled.
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int count_ GUARDED_BY(lock_);
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Mutex lock_ ACQUIRED_AFTER(Locks::abort_lock_);
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ConditionVariable condition_ GUARDED_BY(lock_);
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};
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} // namespace art
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#endif // ART_RUNTIME_BARRIER_H_
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