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

1 files changed, 6 insertions, 4 deletions

diff --git a/include/private/surfaceflinger/SharedBufferStack.h b/include/private/surfaceflinger/SharedBufferStack.h
index d689667..d6ae5e9 100644
--- a/include/private/surfaceflinger/SharedBufferStack.h
+++ b/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];