Add template class SingleStateQueue
Change-Id: If7e2bc9b2a216524ee9cbb68682e2634933b4973
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