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/*
* Copyright (C) 2012 The Android Open Source Project
*
* 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.
*/
#include <new>
#include <cutils/atomic.h>
#include <cutils/atomic-inline.h> // for android_memory_barrier()
#include <media/SingleStateQueue.h>
namespace android {
template<typename T> SingleStateQueue<T>::Mutator::Mutator(Shared *shared)
: mSequence(0), mShared((Shared *) shared)
{
// exactly one of Mutator and Observer must initialize, currently it is Observer
//shared->init();
}
template<typename T> int32_t SingleStateQueue<T>::Mutator::push(const T& value)
{
Shared *shared = mShared;
int32_t sequence = mSequence;
sequence++;
android_atomic_acquire_store(sequence, &shared->mSequence);
shared->mValue = value;
sequence++;
android_atomic_release_store(sequence, &shared->mSequence);
mSequence = sequence;
// consider signalling a futex here, if we know that observer is waiting
return sequence;
}
template<typename T> bool SingleStateQueue<T>::Mutator::ack()
{
return mShared->mAck - mSequence == 0;
}
template<typename T> bool SingleStateQueue<T>::Mutator::ack(int32_t sequence)
{
// this relies on 2's complement rollover to detect an ancient sequence number
return mShared->mAck - sequence >= 0;
}
template<typename T> SingleStateQueue<T>::Observer::Observer(Shared *shared)
: mSequence(0), mSeed(1), mShared((Shared *) shared)
{
// exactly one of Mutator and Observer must initialize, currently it is Observer
shared->init();
}
template<typename T> bool SingleStateQueue<T>::Observer::poll(T& value)
{
Shared *shared = mShared;
int32_t before = shared->mSequence;
if (before == mSequence) {
return false;
}
for (int tries = 0; ; ) {
const int MAX_TRIES = 5;
if (before & 1) {
if (++tries >= MAX_TRIES) {
return false;
}
before = shared->mSequence;
} else {
android_memory_barrier();
T temp = shared->mValue;
int32_t after = android_atomic_release_load(&shared->mSequence);
if (after == before) {
value = temp;
shared->mAck = before;
mSequence = before;
return true;
}
if (++tries >= MAX_TRIES) {
return false;
}
before = after;
}
}
}
#if 0
template<typename T> SingleStateQueue<T>::SingleStateQueue(void /*Shared*/ *shared)
{
((Shared *) shared)->init();
}
#endif
} // namespace android
// hack for gcc
#ifdef SINGLE_STATE_QUEUE_INSTANTIATIONS
#include SINGLE_STATE_QUEUE_INSTANTIATIONS
#endif
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