您不应该尝试在NSOperation 中运行运行循环。 Grand Central Dispatch 拥有运行该操作的线程。您应该启动自己的线程并将其运行循环用于会话流。
However, you need to be aware that NSRunLoop is not generally thread safe, but CFRunLoop is. 这意味着当您想在会话处理线程上运行一个块时，您需要下拉到CFRunLoop 级别。
此外，获得对后台线程运行循环的引用的唯一方法是在该后台线程上运行某些东西。所以第一步是创建你自己的NSThread 子类来导出它自己的运行循环：
typedef void (^MyThreadStartCallback)(CFRunLoopRef runLoop);
@interface MyThread: NSThread
/// After I'm started, I dispatch to the main queue to call `callback`,
// passing my runloop. Then I destroy my reference to `callback`.
- (instancetype)initWithCallback:(MyThreadStartCallback)callback;
@end
@implementation MyThread {
MyThreadStartCallback _callback;
}
- (instancetype)initWithCallback:(MyThreadStartCallback)callback {
if (self = [super init]) {
_callback = callback;
}
return self;
}
- (void)main {
CFRunLoopRef runLoop = CFRunLoopGetCurrent();
dispatch_async(dispatch_get_main_queue(), ^{
_callback(runLoop);
});
_callback = nil;
CFRunLoopRun();
}
@end
现在您可以创建MyThread 的实例，并传入一个回调。当您启动MyThread 时，它将使回调在主线程上运行，并将其自己的（MyThread's）运行循环传递给回调。所以你可以使用MyThread 作为你的会话处理线程，像这样：
@implementation Thing {
CFRunLoopRef _sessionRunLoop;
}
- (void)scheduleStreamsOfSession:(EASession *)session {
MyThread *thread = [[MyThread alloc] initWithCallback:^(CFRunLoopRef runLoop) {
// Here I'm on the main thread, but the session-handling thread has
// started running and its run loop is `runLoop`.
[self scheduleStreamsOfSession:session inRunLoop:runLoop];
}];
[thread start];
}
- (void)scheduleStreamsOfSession:(EASession *)session inRunLoop:(CFRunLoopRef)runLoop {
// Here I'm on the main thread. I'll save away the session-handling run loop
// so I can run more blocks on it later, perhaps to queue data for writing
// to the output stream.
_sessionRunLoop = runLoop;
NSInputStream *inputStream = session.inputStream;
NSOutputStream *outputStream = session.outputStream;
// Here I'm on the main thread, where it's not safe to use the
// session-handling thread's NSRunLoop, so I'll send a block to
// the session-handling thread.
CFRunLoopPerformBlock(runLoop, kCFRunLoopCommonModes, ^{
// Here I'm on the session-handling thread, where it's safe to
// use NSRunLoop to schedule the streams.
NSRunLoop *currentRunLoop = [NSRunLoop currentRunLoop];
[inputStream scheduleInRunLoop:currentRunLoop forMode:NSRunLoopCommonModes];
[outputStream scheduleInRunLoop:currentRunLoop forMode:NSRunLoopCommonModes];
});
// CFRunLoopPerformBlock does **not** wake up the run loop. Since I want
// to make sure the block runs as soon as possible, I have to wake up the
// run loop manually:
CFRunLoopWakeUp(_sessionRunLoop);
}
@end