This basically gets a grip on the graph while doing driver switches operations
on another thread (system thread or audio thread), because those can take time.
Because the graph is refcounted, it'll be freed when the last operation
finishes, which is what we want.
This patch also only allows driver switching when the graph is in state
LIFECYCLE_RUNNING, which is what we want anyway.
--HG--
extra : rebase_source : 76365981ec909796509bd21e616b1ff8602406bd
As noted in the comment, it is very useful to have this interleaved with the ADB
logcat on Android/b2g, because this way we can correlate gecko state with the
state of the Android HAL.
--HG--
extra : rebase_source : 80df45d0851a06daac3abeab2ea4b5bc7e58a21d
In the next patches, when the AudioDriver will be implemented, the audio backend
thread (that we don't control), will return from the stack frame where the
nsTArray that allows the MSG thread to exchange message queues in a efficient
manner with the main thread. We put it in the MediaStreamGraph to avoid adding
an allocation/deallocation per iteration on the MSG thread.
In addition, the graph will be able to run on different threads during its
lifetime, so we can't guarantee a stable stack frame to allocate things on
anymore.
The array are renamed with meaningful names, explaining the double-buffering
pattern: the back queue is filled by the main thread, and is swapped with the
front queue that is processed by the MSG thread.
Arrays accesses are synchronized using the driver's monitor.
