Objective C: How to kill a thread while in another thread in Objective-C?

Question

I was trying to set up a multi thread app. One of the threads is working as background to get some data transfer. Right now this thread automatically kill itself after it's job done. Somehow I need to kill this thread in another thread in order stop its job immediately. Are there any api or method for making this happen?

Answer 1

In short, you can't. Or, more precisely, you should not. Not ever and not under any circumstances.

There is absolutely no way for thread A to know the exact state of thread B when A kills B. If B is holding any locks or in the middle of a system call or calling into a system framework when A kills it, then the resulting state of your application is going to be nondeterministic.

Actually -- it will be somewhat deterministic in that you are pretty much guaranteed that a crash will happen sometime in the near future.

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If you need to terminate thread B, you need to do so in a controlled fashion. The most common way is to have a cancel flag or method that can be set/called. thread B then needs to periodically check this flag or check to see if the method has been called, clean up whatever it is doing, and then exit.

That is, you are going to have to modify the logic in thread B to support this.