NSOperation 是否会产生一个新线程？
很简单，线程（或 NSThread）和 NSOperation 之间是否存在一对一的连接？或者它是否抽象出一个操作，是一种可以由后台多个线程拾取和运行的任务？
Very simply, is there a one to one connection between a thread(or NSThread) and an NSOperation? Or is it abstracted out an operation is kind of a task that can be picked up and run by multiple threads in the background?
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不是一对一的连接，不是。使用 NSOperation 子类的优点是您不需要自己管理多线程。 Apple 甚至（令人困惑地）将典型的
NSOperation子类（即覆盖-main方法的子类）定义为非并发，而不是因为它不不支持并发，但因为并发的细节是由超类管理的：从这个意义上说，
NSOperation子类更像是 NSThread 的目标对象detachNewThreadSelector:toTarget:withObject:。如果您想控制并发行为的方式，另一种方法是在调用
-main之前覆盖-start并根据需要设置并发。这是一个非常好的概述：Managing Concurrency with NSOperation
Not a one-to-one connection, no. The advantage of using
NSOperationsubclasses is that you're not required to manage the multi-threading yourself. Apple even (confusingly) defines the typicalNSOperationsubclass (i.e., one overriding the-mainmethod) as non-concurrent, not because it doesn't support concurrency, but because the details of concurrency are managed by the superclass:In that sense, an
NSOperationsubclass is much more like the target object of NSThread'sdetachNewThreadSelector:toTarget:withObject:.The alternative, if you want control over how the concurrency behaves, is to override
-startand set up concurrency as needed before invoking-main.Here's a very good overview: Managing Concurrency with NSOperation