Exit method of NSRunLoop

1. According to the documentation, if you want to exit runloop, you should not use the first startup method to start Runloop. If no input sources or timers are attached to the run loop, this method exits immediately. If the runloop has no input sources or attached timer, the runloop will exit. If the runloop has no input sources or attached timer, the runloop will exit. Let’s try it. The code looks like this:

NSMachPort *_port; //global NSRunLoop *_theRL; NSThread *_thread; - (void)viewDidLoad {// start a new thread _thread = [[NSThread alloc] initWithTarget:self selector:@selector(createRunLoopInNewThread) object:nil]; [_thread setName:@"com.xindong.thread"]; [_thread start]; } - (void)createRunLoopInNewThread { _theRL = [NSRunLoop currentRunLoop]; _port = (NSMachPort *)[NSMachPort port]; / / add a port to runloop as input source, ensure that can process the message at any time [_theRL addPort: _port forMode: NSDefaultRunLoopMode]; // This method creates a timer in the runloop of the current thread, And execute selector in the current thread [self performSelector:@selector(excuteInNewThread:) withObject:@" Param1 "afterDelay:2]; [self performSelector:@selector(excuteInNewThread:) withObject:@"param2" afterDelay:3]; [_theRL run]; // If the current thread's runloop does not exit, the code after '[_theRL run]' will not be executed. NSLog(@"runloop exited "); // This is executed only when runloop exits. This can be verified by registering runloop observers, but the code will not be posted here. Please check out the code in the demo. } - (void)excuteInNewThread:(NSString *)param { NSLog(@"%@", param); / / removes the current thread port in the runloop [_theRL removePort: _port forMode: NSDefaultRunLoopMode]; }Copy the code

Console output:

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Note: The excuteInNewThread: method has been executed, indicating that runloop has been successfully enabled, otherwise the method will not execute. In the excuteInNewThread: method, port is removed from the current runloop and the runloop exits after the param1 and param2 events are processed (i.e., after the two timer fires). While it is possible to exit the runloop, Apple does not recommend doing so because it is possible to add some input sources to the current thread’s runloop, so manually removing the input source or timer does not guarantee that the runloop will exit.

2. As we know, runloop receives input events from two different sources: input source and timer source. Input sources deliver asynchronous events, usually messages from other threads or programs. The timing source delivers synchronous events that occur at a specific time or at repeated time intervals. Since the run startup mode cannot set a timeout, we will test it by adding a timing source to runloop and modify the above code slightly:

- (void)createRunLoopInNewThread { _theRL = [NSRunLoop currentRunLoop]; / / note: It repeats parameters to be set to ` NO `. NSTimer * timer = [NSTimer scheduledTimerWithTimeInterval: 1.5 repeats: NO block: ^ (NSTimer * _Nonnull timer) { NSLog(@"timer block"); }]; / / add a timing sources [_theRL addTimer: timer forMode: NSDefaultRunLoopMode]; [_theRL run]; // If the current thread's runloop does not exit, the code after '[_theRL run]' will not be executed. NSLog(@"runloop exited "); // This is executed only when runloop exits. This can be verified by registering runloop observers, but the code will not be posted here. Please check out the code in the demo. }Copy the code

The console output is as follows:

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After the timer is triggered, the runloop exits because there is no source to monitor. If you don’t want runloop to exit, simply set the repeats parameter to YES for creating the timer. However, there is an obvious drawback to this setup: Runloops wake up from hibernation every 1.5 seconds, causing unnecessary consumption of CPU resources and system memory. Print by registering a Runloop observer on the console:

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3. Let’s try forcing the thread to exit and see if the current thread’s runloop exits as well. The excuteInNewThread: method is modified as follows:

- (void)createRunLoopInNewThread { _theRL = [NSRunLoop currentRunLoop]; _port = (NSMachPort *)[NSMachPort port]; / / add a port to runloop as input source, ensure that can process the message at any time [_theRL addPort: _port forMode: NSDefaultRunLoopMode]; // This method creates a timer in the runloop of the current thread, And execute selector in the current thread [self performSelector:@selector(excuteInNewThread:) withObject:@" Param1 "afterDelay:2]; [self performSelector:@selector(excuteInNewThread:) withObject:@"param2" afterDelay:3]; [_theRL run]; // If the current thread's runloop does not exit, the code after '[_theRL run]' will not be executed. NSLog(@"runloop exited "); // This is executed only when runloop exits. This can be verified by registering runloop observers, but the code will not be posted here. Please check out the code in the demo. } - (void)excuteInNewThread:(NSString *)param { NSLog(@"%@", param); [NSThread exit]; }Copy the code

Console output:

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When excuteInNewThread: excuteInNewThread: excuteInNewThread: excuteInNewThread: excuteInNewThread: excuteInNewThread: excuteInNewThread: excuteInNewThread: excuteInNewThread: If it does not execute, the current thread’s runloop does not exit, and some resources on the thread stack are not released, causing a memory leak, as shown below. Therefore, this method is not desirable.

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4. At this point, the last exit method left is the CFRunLoopStop function in Core Foundation. Can I exit the runloop using CFRunLoopStop? Let’s test the code with a few modifications:

- (void)createRunLoopInNewThread {// Register runloop observer static CFRunLoopObserverRef _observer; RegisterRunLoopObserver(kCFRunLoopAllActivities, _observer, 0, kCFRunLoopDefaultMode, (__bridge void*)self, RunLoopCallBack); _theRL = [NSRunLoop currentRunLoop]; _port = (NSMachPort *)[NSMachPort port]; [_theRL addPort:_port forMode:NSDefaultRunLoopMode]; [self performSelector:@selector(excuteInNewThread:) withObject:@"param1" afterDelay:2]; [self performSelector:@selector(excuteInNewThread:) withObject:@"param2" afterDelay:3]; [_theRL run]; // If the current thread's runloop does not exit, the code after '[_theRL run]' will not be executed. NSLog(@"runloop exited "); // This is executed only when runloop exits. This can be verified by registering runloop observers, but the code will not be posted here. Please check out the code in the demo. } - (void)excuteInNewThread:(NSString *)param { NSLog(@"%@", param); CFRunLoopStop(CFRunLoopGetCurrent()); }Copy the code

Console output:

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The runloop observer’s callback tells us that the runloop does exit each time the CFRunLoopStop method is executed, but since the run startup repeatedly calls the runMode:beforeDate: method, This will restart runloop after exiting the current runloop, so the NSLog(@” Runloop exited “) method in the above code will not execute. Similarly, the second method, runUntilDate: starting the runloop, cannot be exited using the CFRunLoopStop method.

Starting this way, you can exit runloop by setting a timeout. In addition, it is similar to the first startup method, Run, which is not described here.

Starting this way, the runloop runs once and exits when the timeout expires or the first input source is processed. The test code is as follows:

- (void)createRunLoopInNewThread {// Register runloop observer static CFRunLoopObserverRef _observer; RegisterRunLoopObserver(kCFRunLoopAllActivities, _observer, 0, kCFRunLoopDefaultMode, (__bridge void*)self, RunLoopCallBack); _theRL = [NSRunLoop currentRunLoop]; _port = (NSMachPort *)[NSMachPort port]; [_theRL addPort:_port forMode:NSDefaultRunLoopMode]; [_theRL runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; // If the current thread's runloop does not exit, the code after '[_theRL run]' will not be executed. NSLog(@"runloop exited "); // This is executed only when runloop exits. This can be verified by registering runloop observers, but the code will not be posted here. Please check out the code in the demo. } #pragma mark - Touch - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event { UIColor *color = self.view.backgroundColor; self.view.backgroundColor = color == [UIColor redColor] ? [UIColor yellowColor] : [UIColor redColor]; / / the communication between threads (this is the main thread) [self performSelector: @ the selector (communicateToNewThreadFromMainThread) onThread: _thread withObject:nil waitUntilDone:NO]; } - (void)communicateToNewThreadFromMainThread { NSLog(@"communicate successfully\n\n"); Com.xindong.thread. The first input source event is processed.Copy the code

The console output is as follows:

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When we touch screen, communicateToNewThreadFromMainThread method implemented, namely the input source event is processed, then the runloop exit. If we want to control the exit timing of runloop instead of exiting after processing an input source event, we need to repeatedly call runMode:beforeDate: as described in the Apple documentation:

BOOL shouldKeepRunning = YES; // global
NSRunLoop *theRL = [NSRunLoop currentRunLoop];
while (shouldKeepRunning && [theRL runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]);Copy the code

We then changed the code so that we could control the exit of runloop as follows:

- (void)createRunLoopInNewThread {// Register runloop observer static CFRunLoopObserverRef _observer; RegisterRunLoopObserver(kCFRunLoopAllActivities, _observer, 0, kCFRunLoopDefaultMode, (__bridge void*)self, RunLoopCallBack); _theRL = [NSRunLoop currentRunLoop]; _port = (NSMachPort *)[NSMachPort port]; [_theRL addPort:_port forMode:NSDefaultRunLoopMode]; while (shouldKeepRunning && [_theRL runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]); // If the current thread's runloop does not exit, the code after '[_theRL run]' will not be executed. NSLog(@"runloop exited "); // This is executed only when runloop exits. This can be verified by registering runloop observers, but the code will not be posted here. Please check out the code in the demo. } #pragma mark - Touch - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event { UIColor *color = self.view.backgroundColor; self.view.backgroundColor = color == [UIColor redColor] ? [UIColor yellowColor] : [UIColor redColor]; / / the communication between threads (this is the main thread) [self performSelector: @ the selector (communicateToNewThreadFromMainThread) onThread: _thread withObject:nil waitUntilDone:NO]; } - (void)communicateToNewThreadFromMainThread { NSLog(@"communicate successfully\n\n"); Com.xindong. Thread [self quitRunLoop]; } - (void)quitRunLoop { shouldKeepRunning = NO; CFRunLoopStop(CFRunLoopGetCurrent()); }Copy the code

Starting and exiting the Runloop in this manner causes no memory leaks, no memory growth, and the timing of the exit of the Runloop is freely controlled. Relatively speaking, it is better to use this scheme.

3. To summarize

If you don’t want to exit runloop, you can start runloop in the first way. If you start runloop in the second way, you can exit by setting a timeout. If you use the third method to start runloop, you can exit by setting a timeout or using the CFRunLoopStop method. Demo please stamp here… If there is wrong in the article, but also hope that friends are not stingy corrections. After all, the ability level is limited, can not guarantee accuracy.

References:

Bestswifter.com/runloop-and… Blog.ibireme.com/2015/05/18/… Blog.csdn.net/yxh265/arti… www.dreamingwish.com/frontui/art…