From 5c4cc0d99d3b1cb35c5d7c237272ee53142745fb Mon Sep 17 00:00:00 2001
From: Glenn Kasten <gkasten@google.com>
Date: Mon, 26 Nov 2012 10:40:24 -0800
Subject: Add template class SingleStateQueue

Change-Id: If7e2bc9b2a216524ee9cbb68682e2634933b4973
---
 media/libmedia/SingleStateQueue.cpp | 107 ++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 media/libmedia/SingleStateQueue.cpp

(limited to 'media/libmedia/SingleStateQueue.cpp')

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
-- 
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