Re: Does GCD auto-limit concurrent tasks to number of cores?
Re: Does GCD auto-limit concurrent tasks to number of cores?
- Subject: Re: Does GCD auto-limit concurrent tasks to number of cores?
- From: Carl Hoefs <email@hidden>
- Date: Thu, 09 Apr 2015 12:26:49 -0700
- Importance: Normal
Wonderful! Thank you for clearing this up for me!
-Carl
>
>> On Apr 9, 2015, at 12:07, Carl Hoefs <email@hidden>
>> 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
> email@hidden
>
>
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