> On Apr 9, 2015, at 12:07, Carl Hoefs <newsli...@autonomy.caltech.edu> wrote:
>
> OS X 10.10
>
> I have a highly CPU-bound project that parallelizes well. A small case has
> about 5000 tasks that can execute concurrently (max is ~100,000). I would
> like to use GCD queues to take advantage of the 24 cores I have on my
> MacPro. Does GCD automatically limit the number of tasks that become
> current on its queues to the number of cores (hw.logicalcpu)?
Yes.
> Or is it the
> programmer's responsibility to manage this?
>
> Suppose I do something like this:
>
> dispatch_group_t workgroup = dispatch_group_create();
>
> dispatch_apply(4950,
> dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,
> 0),
> ^(size_t i) {
>
> dispatch_group_enter(workgroup);
>
> // Code block for executing task i . . .
>
> dispatch_group_leave(workgroup);
>
> });
>
> dispatch_group_wait(workgroup, DISPATCH_TIME_FOREVER);
>
Note that your use of a dispatch_group here is redundant; dispatch_apply always
executes synchronously with respect to the caller (i.e. when the above
dispatch_apply has returned, all 4950 executions of your block have already
completed).
--
Clark Smith Cox III
clark....@apple.com
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