This is a brain dump of what happens on b2g when we allocate a new GraphicBuffer from the child side.
entry point: PLayersTransactionChild->SendPGrallocBufferConstructor
- sends synchronous IPC to compositor
Over to b2g/compositor:
on compositor side, this comes in as: PLayerTransactionParent::AllocPGrallocBuffer
- implemented in LayersTransactionParent.cpp - calls GrallocBufferActor::Create(...) - ::Create(...) actually creates the GraphicBuffer* and a GrallocBufferActor* - (The GrallocBufferActor contains a sp<GraphicBuffer> that references the newly-created GraphicBuffer*) - ::Create returns the GrallocBufferActor as a PGrallocBufferParent*, and the GraphicBuffer* as a MaybeMagicGrallocBufferHandle - the GrallocBufferActor/PGrallocBufferParent* is added to the LayerTransactionParent's managed list - the MaybeMagicGrallocBufferHandle is serialized for reply (sending back the fd that represents the GraphicBuffer) -- using code in ShadowLayerUtilsGralloc ParamTraits<MGBH>::Write
Back to child:
- after the sync IPC call, the child receives the MaybeMagicGrallocBufferHandle, using ShadowLayerUtilsGralloc.cpp's ParamTraits<MGBH>::Read - allocates empty GrallocBufferActor() to use a PGrallocBufferChild - the child then sets the previously created GrallocBufferActor/PGrallocBufferChild's mGraphicBuffer to the newly-received sp<GraphicBuffer> - the GrallocBufferActor/PGrallocBufferChild is added to the LayerTransactionChild's managed list - a SurfaceDescriptorGralloc is created using the PGrallocBufferChild, and returned to the caller