fix [2835280] Add support for cancelling buffers to ANativeWindow

There is a new ANativeWindow::cancelBuffer() API that can be used to
cancel any dequeued buffer, BEFORE it's been enqueued. The buffer is
returned to the list of availlable buffers. dequeue and cancel are not
mutually thread safe, they must be called from the same thread or
external synchronization must be used.

Change-Id: I86cc7985bace8b6a93ad2c75d2bef5c3c2cb4d61

include/private/surfaceflinger/SharedBufferStack.h

@@ -114,8 +114,9 @@ public:
 
     int32_t     identity;       // surface's identity (const)
     int32_t     token;          // surface's token (for debugging)
-    int32_t     reserved32[1];
     Statistics  stats;
+    int8_t      headBuf;        // last retired buffer
+    uint8_t     reservedBytes[3];
     int32_t     reserved;
     BufferData  buffers[NUM_BUFFER_MAX];     // 1024 bytes
 };
@@ -201,6 +202,7 @@ public:
     status_t undoDequeue(int buf);
     
     status_t lock(int buf);
+    status_t cancel(int buf);
     status_t queue(int buf);
     bool needNewBuffer(int buffer) const;
     status_t setDirtyRegion(int buffer, const Region& reg);
@@ -230,8 +232,9 @@ private:
         inline ssize_t operator()();
     };
 
-    struct UndoDequeueUpdate : public UpdateBase {
-        inline UndoDequeueUpdate(SharedBufferBase* sbb);
+    struct CancelUpdate : public UpdateBase {
+        int tail, buf;
+        inline CancelUpdate(SharedBufferBase* sbb, int tail, int buf);
         inline ssize_t operator()();
     };
 
@@ -256,7 +259,6 @@ private:
     int mNumBuffers;
 
     int32_t tail;
-    int32_t undoDequeueTail;
     int32_t queued_head;
     // statistics...
     nsecs_t mDequeueTime[SharedBufferStack::NUM_BUFFER_MAX];

include/surfaceflinger/Surface.h

@@ -199,6 +199,7 @@ private:
      */
     static int setSwapInterval(ANativeWindow* window, int interval);
     static int dequeueBuffer(ANativeWindow* window, android_native_buffer_t** buffer);
+    static int cancelBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int lockBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int queueBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int query(ANativeWindow* window, int what, int* value);
@@ -207,6 +208,7 @@ private:
     int dequeueBuffer(android_native_buffer_t** buffer);
     int lockBuffer(android_native_buffer_t* buffer);
     int queueBuffer(android_native_buffer_t* buffer);
+    int cancelBuffer(android_native_buffer_t* buffer);
     int query(int what, int* value);
     int perform(int operation, va_list args);
 

include/ui/egl/android_natives.h

@@ -218,7 +218,17 @@ struct ANativeWindow
     int     (*perform)(struct ANativeWindow* window,
                 int operation, ... );
     
-    void* reserved_proc[3];
+    /*
+     * hook used to cancel a buffer that has been dequeued.
+     * No synchronization is performed between dequeue() and cancel(), so
+     * either external synchronization is needed, or these functions must be
+     * called from the same thread.
+     */
+    int     (*cancelBuffer)(struct ANativeWindow* window,
+                struct android_native_buffer_t* buffer);
+
+
+    void* reserved_proc[2];
 };
 
 // Backwards compatibility...  please switch to ANativeWindow.

libs/surfaceflinger_client/SharedBufferStack.cpp

@@ -285,10 +285,12 @@ ssize_t SharedBufferClient::DequeueUpdate::operator()() {
     return NO_ERROR;
 }
 
-SharedBufferClient::UndoDequeueUpdate::UndoDequeueUpdate(SharedBufferBase* sbb)
-    : UpdateBase(sbb) {    
+SharedBufferClient::CancelUpdate::CancelUpdate(SharedBufferBase* sbb,
+        int tail, int buf)
+    : UpdateBase(sbb), tail(tail), buf(buf) {
 }
-ssize_t SharedBufferClient::UndoDequeueUpdate::operator()() {
+ssize_t SharedBufferClient::CancelUpdate::operator()() {
+    stack.index[tail] = buf;
     android_atomic_inc(&stack.available);
     return NO_ERROR;
 }
@@ -319,7 +321,7 @@ ssize_t SharedBufferServer::RetireUpdate::operator()() {
         return BAD_VALUE;
 
     // Preventively lock the current buffer before updating queued.
-    android_atomic_write(stack.index[head], &stack.inUse);
+    android_atomic_write(stack.headBuf, &stack.inUse);
 
     // Decrement the number of queued buffers 
     int32_t queued;
@@ -334,7 +336,9 @@ ssize_t SharedBufferServer::RetireUpdate::operator()() {
     // the buffer we preventively locked upon entering this function
 
     head = (head + 1) % numBuffers;
-    android_atomic_write(stack.index[head], &stack.inUse);
+    const int8_t headBuf = stack.index[head];
+    stack.headBuf = headBuf;
+    android_atomic_write(headBuf, &stack.inUse);
 
     // head is only modified here, so we don't need to use cmpxchg
     android_atomic_write(head, &stack.head);
@@ -359,7 +363,7 @@ ssize_t SharedBufferServer::StatusUpdate::operator()() {
 SharedBufferClient::SharedBufferClient(SharedClient* sharedClient,
         int surface, int num, int32_t identity)
     : SharedBufferBase(sharedClient, surface, identity),
-      mNumBuffers(num), tail(0), undoDequeueTail(0)
+      mNumBuffers(num), tail(0)
 {
     SharedBufferStack& stack( *mSharedStack );
     tail = computeTail();
@@ -395,7 +399,6 @@ ssize_t SharedBufferClient::dequeue()
     DequeueUpdate update(this);
     updateCondition( update );
 
-    undoDequeueTail = tail;
     int dequeued = stack.index[tail];
     tail = ((tail+1 >= mNumBuffers) ? 0 : tail+1);
     LOGD_IF(DEBUG_ATOMICS, "dequeued=%d, tail++=%d, %s",
@@ -407,15 +410,20 @@ ssize_t SharedBufferClient::dequeue()
 }
 
 status_t SharedBufferClient::undoDequeue(int buf)
+{
+    return cancel(buf);
+}
+
+status_t SharedBufferClient::cancel(int buf)
 {
     RWLock::AutoRLock _rd(mLock);
 
-    // TODO: we can only undo the previous dequeue, we should
-    // enforce that in the api
-    UndoDequeueUpdate update(this);
+    // calculate the new position of the tail index (essentially tail--)
+    int localTail = (tail + mNumBuffers - 1) % mNumBuffers;
+    CancelUpdate update(this, localTail, buf);
     status_t err = updateCondition( update );
     if (err == NO_ERROR) {
-        tail = undoDequeueTail;
+        tail = localTail;
     }
     return err;
 }

libs/surfaceflinger_client/Surface.cpp

@@ -409,6 +409,7 @@ void Surface::init()
 {
     ANativeWindow::setSwapInterval  = setSwapInterval;
     ANativeWindow::dequeueBuffer    = dequeueBuffer;
+    ANativeWindow::cancelBuffer     = cancelBuffer;
     ANativeWindow::lockBuffer       = lockBuffer;
     ANativeWindow::queueBuffer      = queueBuffer;
     ANativeWindow::query            = query;
@@ -517,6 +518,12 @@ int Surface::dequeueBuffer(ANativeWindow* window,
     return self->dequeueBuffer(buffer);
 }
 
+int Surface::cancelBuffer(ANativeWindow* window,
+        android_native_buffer_t* buffer) {
+    Surface* self = getSelf(window);
+    return self->cancelBuffer(buffer);
+}
+
 int Surface::lockBuffer(ANativeWindow* window, 
         android_native_buffer_t* buffer) {
     Surface* self = getSelf(window);
@@ -617,6 +624,33 @@ int Surface::dequeueBuffer(android_native_buffer_t** buffer)
     return err;
 }
 
+int Surface::cancelBuffer(android_native_buffer_t* buffer)
+{
+    status_t err = validate();
+    switch (err) {
+    case NO_ERROR:
+        // no error, common case
+        break;
+    case INVALID_OPERATION:
+        // legitimate errors here
+        return err;
+    default:
+        // other errors happen because the surface is now invalid,
+        // for instance because it has been destroyed. In this case,
+        // we just fail silently (canceling a buffer is not technically
+        // an error at this point)
+        return NO_ERROR;
+    }
+
+    int32_t bufIdx = getBufferIndex(GraphicBuffer::getSelf(buffer));
+
+    err = mSharedBufferClient->cancel(bufIdx);
+
+    LOGE_IF(err, "error canceling buffer %d (%s)", bufIdx, strerror(-err));
+    return err;
+}
+
+
 int Surface::lockBuffer(android_native_buffer_t* buffer)
 {
     status_t err = validate();