Add template class StateQueue

Change-Id: Iccc5eb42bc295a22b2e429a4551f083cd7b6831a

3 files changed, 229 insertions, 0 deletions

diff --git a/services/audioflinger/Android.mk b/services/audioflinger/Android.mk
index 2cf77ce..2f78a7e 100644
--- a/services/audioflinger/Android.mk
+++ b/services/audioflinger/Android.mk
@@ -34,6 +34,8 @@ LOCAL_SRC_FILES:=               \
 #   AudioResamplerSinc.cpp.arm
 #   AudioResamplerCubic.cpp.arm
 
+LOCAL_SRC_FILES += StateQueue.cpp
+
 LOCAL_C_INCLUDES := \
     $(call include-path-for, audio-effects) \
     $(call include-path-for, audio-utils)
diff --git a/services/audioflinger/StateQueue.cpp b/services/audioflinger/StateQueue.cpp
new file mode 100644
index 0000000..ae263f5
--- /dev/null
+++ b/services/audioflinger/StateQueue.cpp
@@ -0,0 +1,133 @@
+/*
+ * 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.
+ */
+
+#define LOG_TAG "StateQueue"
+//#define LOG_NDEBUG 0
+
+#include <time.h>
+#include <cutils/atomic.h>
+#include <utils/Log.h>
+#include "StateQueue.h"
+
+namespace android {
+
+// Constructor and destructor
+
+template<typename T> StateQueue<T>::StateQueue() :
+    mNext(NULL), mAck(NULL), mCurrent(NULL),
+    mMutating(&mStates[0]), mExpecting(NULL),
+    mInMutation(false), mIsDirty(false), mIsInitialized(false)
+{
+}
+
+template<typename T> StateQueue<T>::~StateQueue()
+{
+}
+
+// Observer APIs
+
+template<typename T> const T* StateQueue<T>::poll()
+{
+    const T *next = (const T *) android_atomic_acquire_load((volatile int32_t *) &mNext);
+    if (next != mCurrent) {
+        mAck = next;    // no additional barrier needed
+        mCurrent = next;
+    }
+    return next;
+}
+
+// Mutator APIs
+
+template<typename T> T* StateQueue<T>::begin()
+{
+    ALOG_ASSERT(!mInMutation, "begin() called when in a mutation");
+    mInMutation = true;
+    return mMutating;
+}
+
+template<typename T> void StateQueue<T>::end(bool didModify)
+{
+    ALOG_ASSERT(mInMutation, "end() called when not in a mutation");
+    ALOG_ASSERT(mIsInitialized || didModify, "first end() must modify for initialization");
+    if (didModify) {
+        mIsDirty = true;
+        mIsInitialized = true;
+    }
+    mInMutation = false;
+}
+
+template<typename T> bool StateQueue<T>::push(StateQueue<T>::block_t block)
+{
+#define PUSH_BLOCK_ACK_NS    3000000L   // 3 ms: time between checks for ack in push()
+                                        //       FIXME should be configurable
+    static const struct timespec req = {0, PUSH_BLOCK_ACK_NS};
+
+    ALOG_ASSERT(!mInMutation, "push() called when in a mutation");
+
+    if (mIsDirty) {
+
+        // wait for prior push to be acknowledged
+        if (mExpecting != NULL) {
+            for (;;) {
+                const T *ack = (const T *) mAck;    // no additional barrier needed
+                if (ack == mExpecting) {
+                    // unnecessary as we're about to rewrite
+                    //mExpecting = NULL;
+                    break;
+                }
+                if (block == BLOCK_NEVER) {
+                    return false;
+                }
+                nanosleep(&req, NULL);
+            }
+        }
+
+        // publish
+        android_atomic_release_store((int32_t) mMutating, (volatile int32_t *) &mNext);
+        mExpecting = mMutating;
+
+        // copy with circular wraparound
+        if (++mMutating >= &mStates[kN]) {
+            mMutating = &mStates[0];
+        }
+        *mMutating = *mExpecting;
+        mIsDirty = false;
+
+    }
+
+    // optionally wait for this push or a prior push to be acknowledged
+    if (block == BLOCK_UNTIL_ACKED) {
+        if (mExpecting != NULL) {
+            for (;;) {
+                const T *ack = (const T *) mAck;    // no additional barrier needed
+                if (ack == mExpecting) {
+                    mExpecting = NULL;
+                    break;
+                }
+                nanosleep(&req, NULL);
+            }
+        }
+    }
+
+    return true;
+}
+
+}   // namespace android
+
+// hack for gcc
+#ifdef STATE_QUEUE_INSTANTIATIONS
+#include STATE_QUEUE_INSTANTIATIONS
+#endif
diff --git a/services/audioflinger/StateQueue.h b/services/audioflinger/StateQueue.h
new file mode 100644
index 0000000..fe72ddc
--- /dev/null
+++ 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