Add template class SingleStateQueue
Change-Id: If7e2bc9b2a216524ee9cbb68682e2634933b4973
diff --git a/include/media/SingleStateQueue.h b/include/media/SingleStateQueue.h
new file mode 100644
index 0000000..04c5fd0
--- /dev/null
+++ b/include/media/SingleStateQueue.h
@@ -0,0 +1,97 @@
+/*
+ * 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 SINGLE_STATE_QUEUE_H
+#define SINGLE_STATE_QUEUE_H
+
+// Non-blocking single element state queue, or
+// Non-blocking single-reader / single-writer multi-word atomic load / store
+
+#include <stdint.h>
+
+namespace android {
+
+template<typename T> class SingleStateQueue {
+
+public:
+
+ class Mutator;
+ class Observer;
+
+ struct Shared {
+ // needs to be part of a union so don't define constructor or destructor
+
+ friend class Mutator;
+ friend class Observer;
+
+private:
+ void init() { mAck = 0; mSequence = 0; }
+
+ volatile int32_t mAck;
+#if 0
+ int mPad[7];
+ // cache line boundary
+#endif
+ volatile int32_t mSequence;
+ T mValue;
+ };
+
+ class Mutator {
+ public:
+ Mutator(Shared *shared);
+ /*virtual*/ ~Mutator() { }
+
+ // push new value onto state queue, overwriting previous value;
+ // returns a sequence number which can be used with ack()
+ int32_t push(const T& value);
+
+ // return true if most recent push has been observed
+ bool ack();
+
+ // return true if a push with specified sequence number or later has been observed
+ bool ack(int32_t sequence);
+
+ private:
+ int32_t mSequence;
+ Shared * const mShared;
+ };
+
+ class Observer {
+ public:
+ Observer(Shared *shared);
+ /*virtual*/ ~Observer() { }
+
+ // return true if value has changed
+ bool poll(T& value);
+
+ private:
+ int32_t mSequence;
+ int mSeed; // for PRNG
+ Shared * const mShared;
+ };
+
+#if 0
+ SingleStateQueue(void /*Shared*/ *shared);
+ /*virtual*/ ~SingleStateQueue() { }
+
+ static size_t size() { return sizeof(Shared); }
+#endif
+
+};
+
+} // namespace android
+
+#endif // SINGLE_STATE_QUEUE_H