If the this spawns its own thread for pulling buffers from upstream it should call this method after it has pulled a buffer.
If the element needed to preroll, this function will perform the preroll and will then block until the element state is changed.
This function should be called with the PREROLL_LOCK held.
| this |
the sink |
| obj |
the mini object that caused the preroll |
|
OK if the preroll completed and processing can continue. Any other return value should be returned from the render vmethod. |