Created attachment 328431 [details]
Test case demonstrating race

While changing the state of a child, we might receive ASYNC_START messages which we will store for future matching.

If that child state change returns NO_PREROLL we will ignore the ASYNC messages and successfully change the state of the child, BUT the stored ASYNC_START message is still there.

As the state was changed the child might not have a pending state when the ASYNC_DONE message is sent by it's internal elements. If that happens the ASYNC_DONE message is not propagated to the parent bin and the stored ASYNC_START message is orphaned preventing the parent bin to complete its own state change.

I am providing a test case demonstrating that race which has been tested with 1.6.2, 1.6.4 and 1.8.1

The test cases uses a sample JPEG file which is being opened by 2 different bins using uridecodebin (both of them generating ASYNC_* messages) but one of the bins also has identity with sync=TRUE which triggers a NO_PREROLL. If there's a slight delay between changing states from PAUSED to PLAYING the no_preroll_bin will eat the ASYNC_DONE message leaving the pipeline in a transitioning state.

My proposed fix for this bug would be to delete stored ASYNC_START messages from child in the parent bin when child returns NO_PREROLL (attached patch).