what are the meanings of apple xcode threads when debuging an iphone application?

when I debug an iphone application, xcode laun开发者_运维技巧ch 4 threads, such as thread 1,thread 2 ,thread 3 and thread 4.is anyone knows the usage of these threads?

It just depends on what the system is doing. Often there is a background network processing thread, and there can be background UI threads.

You can usually get an idea by stopping the debugger at a break point and switching threads to see what the call stacks look like.