Add template class StateQueue
Change-Id: Iccc5eb42bc295a22b2e429a4551f083cd7b6831a
diff --git a/services/audioflinger/StateQueue.h b/services/audioflinger/StateQueue.h
new file mode 100644
index 0000000..fe72ddc
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+++ b/services/audioflinger/StateQueue.h
@@ -0,0 +1,94 @@
+/*
+ * 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.
+ */
+
+#ifndef ANDROID_AUDIO_STATE_QUEUE_H
+#define ANDROID_AUDIO_STATE_QUEUE_H
+
+namespace android {
+
+// manages a FIFO queue of states
+template<typename T> class StateQueue {
+
+public:
+ StateQueue();
+ virtual ~StateQueue();
+
+ // Observer APIs
+
+ // Poll for a state change. Returns a pointer to a read-only state,
+ // or NULL if the state has not been initialized yet.
+ // If a new state has not pushed by mutator since the previous poll,
+ // then the returned pointer will be unchanged.
+ // The previous state pointer is guaranteed to still be valid;
+ // this allows the observer to diff the previous and new states.
+ const T* poll();
+
+ // Mutator APIs
+
+ // Begin a mutation. Returns a pointer to a read/write state, except the
+ // first time it is called the state is write-only and _must_ be initialized.
+ // Mutations cannot be nested.
+ // If the state is dirty and has not been pushed onto the state queue yet, then
+ // this new mutation will be squashed together with the previous one.
+ T* begin();
+
+ // End the current mutation and indicate whether caller modified the state.
+ // If didModify is true, then the state is marked dirty (in need of pushing).
+ // There is no rollback option because modifications are done in place.
+ // Does not automatically push the new state onto the state queue.
+ void end(bool didModify = true);
+
+ // Push a new state, if any, out to the observer via the state queue.
+ // For BLOCK_NEVER, returns:
+ // true if not dirty, or dirty and pushed successfully
+ // false if dirty and not pushed because that would block; remains dirty
+ // For BLOCK_UNTIL_PUSHED and BLOCK_UNTIL_ACKED, always returns true.
+ // No-op if there are no pending modifications (not dirty), except
+ // for BLOCK_UNTIL_ACKED it will wait until a prior push has been acknowledged.
+ // Must not be called in the middle of a mutation.
+ enum block_t {
+ BLOCK_NEVER, // do not block
+ BLOCK_UNTIL_PUSHED, // block until there's a slot available for the push
+ BLOCK_UNTIL_ACKED, // also block until the push is acknowledged by the observer
+ };
+ bool push(block_t block = BLOCK_NEVER);
+
+ // Return whether the current state is dirty (modified and not pushed).
+ bool isDirty() const { return mIsDirty; }
+
+private:
+ static const unsigned kN = 4; // values != 4 are not supported by this code
+ T mStates[kN]; // written by mutator, read by observer
+
+ // "volatile" is meaningless with SMP, but here it indicates that we're using atomic ops
+ volatile const T* mNext; // written by mutator to advance next, read by observer
+ volatile const T* mAck; // written by observer to acknowledge advance of next, read by mutator
+
+ // only used by observer
+ const T* mCurrent; // most recent value returned by poll()
+
+ // only used by mutator
+ T* mMutating; // where updates by mutator are done in place
+ const T* mExpecting; // what the mutator expects mAck to be set to
+ bool mInMutation; // whether we're currently in the middle of a mutation
+ bool mIsDirty; // whether mutating state has been modified since last push
+ bool mIsInitialized; // whether mutating state has been initialized yet
+
+}; // class StateQueue
+
+} // namespace android
+
+#endif // ANDROID_AUDIO_STATE_QUEUE_H