libgui: Allow an IGBProducer to disable allocation

Adds a new method IGBP::allowAllocation, which controls whether
dequeueBuffer is permitted to allocate a new buffer. If allocation is
disallowed, dequeueBuffer will block or return an error as it
normally would (as controlled by *ControlledByApp).

If there are free buffers, but they are not of the correct dimensions,
format, or usage, they may be freed if a more suitable buffer is not
found first.

Bug: 19801715
Change-Id: I0d604958b78b2fd775c2547690301423f9a52165

3 files changed, 19 insertions, 0 deletions

diff --git a/include/gui/BufferQueueCore.h b/include/gui/BufferQueueCore.h
index a6065a9..9a43516 100644
--- a/include/gui/BufferQueueCore.h
+++ b/include/gui/BufferQueueCore.h
@@ -266,6 +266,10 @@ private:
     // mIsAllocatingCondition is a condition variable used by producers to wait until mIsAllocating
     // becomes false.
     mutable Condition mIsAllocatingCondition;
+
+    // mAllowAllocation determines whether dequeueBuffer is allowed to allocate
+    // new buffers
+    bool mAllowAllocation;
 }; // class BufferQueueCore
 
 } // namespace android
diff --git a/include/gui/BufferQueueProducer.h b/include/gui/BufferQueueProducer.h
index f794ea3..ed660fb 100644
--- a/include/gui/BufferQueueProducer.h
+++ b/include/gui/BufferQueueProducer.h
@@ -172,6 +172,9 @@ public:
     virtual void allocateBuffers(bool async, uint32_t width, uint32_t height,
             PixelFormat format, uint32_t usage);
 
+    // See IGraphicBufferProducer::allowAllocation
+    virtual status_t allowAllocation(bool allow);
+
 private:
     // This is required by the IBinder::DeathRecipient interface
     virtual void binderDied(const wp<IBinder>& who);
diff --git a/include/gui/IGraphicBufferProducer.h b/include/gui/IGraphicBufferProducer.h
index 2d99f24..5c50b2b 100644
--- a/include/gui/IGraphicBufferProducer.h
+++ b/include/gui/IGraphicBufferProducer.h
@@ -458,6 +458,18 @@ public:
     // allocated, this function has no effect.
     virtual void allocateBuffers(bool async, uint32_t width, uint32_t height,
             PixelFormat format, uint32_t usage) = 0;
+
+    // Sets whether dequeueBuffer is allowed to allocate new buffers.
+    //
+    // Normally dequeueBuffer does not discriminate between free slots which
+    // already have an allocated buffer and those which do not, and will
+    // allocate a new buffer if the slot doesn't have a buffer or if the slot's
+    // buffer doesn't match the requested size, format, or usage. This method
+    // allows the producer to restrict the eligible slots to those which already
+    // have an allocated buffer of the correct size, format, and usage. If no
+    // eligible slot is available, dequeueBuffer will block or return an error
+    // as usual.
+    virtual status_t allowAllocation(bool allow) = 0;
 };
 
 // ----------------------------------------------------------------------------