If the current thread is operating in a ForkJoinPool,
unschedules and returns, without executing, a task externally
submitted to the pool, if one is available. Availability may be
transient, so a {@code null} result does not necessarily imply
quiescence of the pool. This method is designed primarily to
support extensions, and is unlikely to be useful otherwise.
@return a task, or {@code null} if none are available
If the current thread is operating in a ForkJoinPool, unschedules and returns, without executing, a task externally submitted to the pool, if one is available. Availability may be transient, so a {@code null} result does not necessarily imply quiescence of the pool. This method is designed primarily to support extensions, and is unlikely to be useful otherwise.
@return a task, or {@code null} if none are available