Return fence to client in dequeuBuffer

Change-Id: Ic19750793ad993f0e85391f3cabd743ba565d4c9

include/ui/Fence.h

@@ -69,6 +69,11 @@ public:
     static sp<Fence> merge(const String8& name, const sp<Fence>& f1,
             const sp<Fence>& f2);
 
+    // Return a duplicate of the fence file descriptor. The caller is
+    // responsible for closing the returned file descriptor. On error, -1 will
+    // be returned and errno will indicate the problem.
+    int dup() const;
+
     // Flattenable interface
     size_t getFlattenedSize() const;
     size_t getFdCount() const;

libs/gui/SurfaceTextureClient.cpp

@@ -222,15 +222,18 @@ int SurfaceTextureClient::dequeueBuffer(android_native_buffer_t** buffer,
     }
 
     if (fence.get()) {
-        status_t err = fence->wait(Fence::TIMEOUT_NEVER);
-        if (err != OK) {
-            ALOGE("dequeueBuffer: error waiting for fence: %d", err);
+        *fenceFd = fence->dup();
+        if (*fenceFd == -1) {
+            ALOGE("dequeueBuffer: error duping fence: %d", errno);
+            // dup() should never fail; something is badly wrong. Soldier on
+            // and hope for the best; the worst that should happen is some
+            // visible corruption that lasts until the next frame.
         }
-        fence.clear();
+    } else {
+        *fenceFd = -1;
     }
 
     *buffer = gbuf.get();
-    *fenceFd = -1;
     return OK;
 }
 

libs/ui/Fence.cpp

@@ -62,6 +62,10 @@ sp<Fence> Fence::merge(const String8& name, const sp<Fence>& f1,
     return sp<Fence>(new Fence(result));
 }
 
+int Fence::dup() const {
+    return ::dup(mFenceFd);
+}
+
 size_t Fence::getFlattenedSize() const {
     return 0;
 }