BQ: Add support for single buffer mode

- Adds a single buffer mode to BufferQueue. In this mode designate the
  first dequeued buffer as the shared buffer. All calls to dequeue()
  and acquire() will then return the shared buffer, allowing the
  producer and consumer to share it.
- Modify the buffer slot state tracking. Add a new SHARED state for
  the shared buffer in single buffer mode. Also track how many times
  a buffer has been dequeued/queued/acquired as it's possible for a
  shared buffer to be both dequeued and acquired at the same time, or
  dequeued/acquired multiple times. This tracking is needed to know
  when to drop the buffer out of the SHARED state after single buffer
  mode has been disabled.
- Add plumbing for enabling/disabling single buffer mode from Surface.

Bug 24940410

Change-Id: I3fc550c74bacb5523c049a227111356257386853

1 files changed, 23 insertions, 8 deletions

diff --git a/libs/gui/BufferSlot.cpp b/libs/gui/BufferSlot.cpp
index 01595de448..b1cdc5d5f3 100644
--- a/libs/gui/BufferSlot.cpp
+++ b/libs/gui/BufferSlot.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 The Android Open Source Project
+ * Copyright 2015 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.
@@ -18,14 +18,29 @@
 
 namespace android {
 
-const char* BufferSlot::bufferStateName(BufferState state) {
-    switch (state) {
-        case BufferSlot::DEQUEUED: return "DEQUEUED";
-        case BufferSlot::QUEUED: return "QUEUED";
-        case BufferSlot::FREE: return "FREE";
-        case BufferSlot::ACQUIRED: return "ACQUIRED";
+
+const char* BufferState::string() const {
+
+    if (isShared()) {
+        return "SHARED";
+    }
+
+    if (isFree()) {
+        return "FREE";
+    }
+
+    if (isAcquired()) {
+        return "ACQUIRED";
+    }
+
+    if (isDequeued()) {
+        return "DEQUEUED";
+    }
+
+    if (isQueued()) {
+        return "QUEUED";
     }
-    return "Unknown";
+    return "UNKNOWN";
 }
 
 } // namespace android