diff options
Diffstat (limited to 'media/libmedia/SingleStateQueue.cpp')
-rw-r--r-- | media/libmedia/SingleStateQueue.cpp | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/media/libmedia/SingleStateQueue.cpp b/media/libmedia/SingleStateQueue.cpp new file mode 100644 index 0000000..3503baa --- /dev/null +++ b/media/libmedia/SingleStateQueue.cpp @@ -0,0 +1,107 @@ +/* + * 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 |