Description: Async OSC create to avoid the blocking unnecessarily.
Details    : If a OST has no remain object, system will block on the creating
            when need to create a new object on this OST. Now, ways use
            pre-created objects when available, instead of blocking on an
            empty osc while others are not empty.  If we must block, we block
            for the shortest possible period of time.

Patch by shadow.

b=4900
i=wangdi
i=nathan