Removes all available unexecuted submitted and forked tasks
from scheduling queues and adds them to the given collection,
without altering their execution status. These may include
artificially generated or wrapped tasks. This method is
designed to be invoked only when the pool is known to be
quiescent. Invocations at other times may not remove all
tasks. A failure encountered while attempting to add elements
to collection {@code c} may result in elements being in
neither, either or both collections when the associated
exception is thrown. The behavior of this operation is
undefined if the specified collection is modified while the
operation is in progress.
@param c the collection to transfer elements into
@return the number of elements transferred
Removes all available unexecuted submitted and forked tasks from scheduling queues and adds them to the given collection, without altering their execution status. These may include artificially generated or wrapped tasks. This method is designed to be invoked only when the pool is known to be quiescent. Invocations at other times may not remove all tasks. A failure encountered while attempting to add elements to collection {@code c} may result in elements being in neither, either or both collections when the associated exception is thrown. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress.
@param c the collection to transfer elements into @return the number of elements transferred