Thread Explosion for the Global Queues and NSOperationQueues

Question

happy OP

Created Jul ’16

Replies 4

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In this WWDC video,

https://developer.apple.com/videos/play/wwdc2015/718/?time=1509

they talked about possible thread explosions.

Thread explosions can occur if you send lots of async blocks to a non-serial dispatch queue.

Questions:

Can thread explosion happen too if you have lots of serial dispatch queues, for example, 100?
Can thread explosion also happen to 1 non-serial (maxConcurrentOperationCount not 1) NSOperationQueue?
Can thread explosion also happen if you have lots of seriall (maxConcurrentOperationCount is 1) NSOperationQueues, for example, 100?
Can thread explosion happen to the global queues? Or are they regulated in some way to avoid thread explosions?

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Answer 1

QuinceyMorris OP

Jul ’16

AFAIK, thread explosion can't occur on serial queues, because there can never be a need for more than one thread per serial queue. However, having hundreds of serial queues doesn't seem like a great idea.

>> Can thread explosion happen to the global queues?

Oh, yes.

I think the point is to structure your code in terms of your work units (closures), however small they are, generally queuing other work units as they complete. This is in contrast to generating all of the work units initially, and expecting the system to schedule them rationally. The latter is not a stupid concept, but the system just doesn't work that way.

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Answer 2

DTS Engineer OP

Apple

Jul ’16

The main thing to worry about is doing work that may require that the thread waits.

Yeah, this.

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Answer 3

happy OP

Jul ’16

Can you explain why having lots of serial queues is not a great idea?

What are the pitfalls / drawbacks of using this approach?

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