Hi Daniel,
If a queue A has its target set to queue B and queue B is suspended with dispatch_suspend(B), why are blocks from queue A still executed?
they are not, but unless dispatch_suspend(B) is executed from B itself, suspension is asynchronous and non-preemptive, i.e. suspension only takes effect when queue state is checked before the next item on B is executed (but does not affect the current item on B).
I knew that it was non-preemptive, but I was not aware it was also asynchronous. But the manpage describes it that way, so I should have known.
(queue A as a whole is a single workitem on queue B so queue A may stay the "current item" on queue B for many items on A)
That was the missing bit to complete my mental picture. Thanks a lot for your explanation. Michael