一、Runloop简介：
Run loops 是线程相关的的基础框架的一部分。一个 run loop 就是一个事件处理 的循环,用来不停的调度工作以及处理输入事件。
使用 run loop的目的是让你的线程在有工作的时候忙于工作,而没工作的时候处于休眠状态。
Runloop还可以在loop在循环中的同时响应其他输入源，比如界面控件的按钮，手势等。
Run loop 接收输入事件来自两种不同的来源:
输入源(input source)和定时源 (timer source)。
输入源传递异步事件,通常消息来自于其他线程或程序。输入源的种类:基于端口的输入源和自定义输入源。
定时源则传递同步事件,发生在特定时间或者重复的时间间隔。
Run loop 模式是所有要监视的输入源和定时源以及要通知的 run loop 注册观察 者的集合。
可以将 Run loop 观察者和以下事件关联:
Run loop 入口
Run loop 何时处理一个定时器
Run loop 何时处理一个输入源
Run loop 何时进入睡眠状态
Run loop 何时被唤醒,但在唤醒之前要处理的事件
Run loop 终止
每次运行 Run loop,你线程的 Run loop 对会自动处理之前未处理的消息,并通知相关的观察者。具体的顺序如下:
1. 通知观察者 Run loop 已经启动。
2. 通知观察者任何即将要开始的定时器。
3. 通知观察者任何即将启动的非基于端口的源。
4. 启动任何准备好的非基于端口的源。
5. 如果基于端口的源准备好并处于等待状态,立即启动;并进入步骤 9。
6. 通知观察者线程进入休眠。
7. 将线程置于休眠直到任一下面的事件发生:
某一事件到达基于端口的源；
定时器启动；
Run loop 设置的时间已经超时；
Run loop 被显式唤醒。
8. 通知观察者线程将被唤醒。
9. 处理未处理的事件
如果用户定义的定时器启动,处理定时器事件并重启 Run loop。进入步骤 2。
如果输入源启动,传递相应的消息。
如果 Run loop 被显式唤醒而且时间还没超时,重启 Run loop，进入步骤 2。
10. 通知观察者 Run loop 结束。
Run loop 在你要和线程有更多的交互时才需要,比如以下情况:
使用端口或自定义输入源来和其他线程通信；
使用线程的定时器；
Cocoa 中使用任何performSelector...的方法；
使线程周期性工作。
二、举例说明Runloop的优点。
一般情况下，当我们使用NSRunLoop的时候，代码如下所示：
do {
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopModebeforeDate:[NSDate distantFuture]];
} while (!done);
在上面的代码中，参数done为NO的时候，当前runloop会一直接收处理其他输入源，处理输入源之后会再回到runloop中等待其他的输入源；除非done为NO，否则当前流程一直再runloop中。
如下面的代码片段所示，有三个按钮，分别对应如下三个action消息，buttonNormalThreadTestPressed，buttonRunloopPressed，buttonTestPressed。
buttonNormalThreadTestPressed：启动一个线程，在while循环中等待线程执行完再接着往下运行。
buttonRunloopPressed：启动一个线程，使用runloop，等待线程执行完再接着往下运行。
buttonTestPressed：仅仅打印两条日志，用来测试UI是否能立即响应的。
在本测试中，待程序运行后，做如下操作对比：
1、点击buttonNormalThreadTestPressed，然后立刻点击buttonTestPressed，查看日志输出。
2、待1完成后，点击buttonRunloopPressed，然后立刻点击buttonTestPressed，查看日志输出，跟1的日志做对比，即可以发现步骤2即使线程没有完成，在runloop等待过程中，界面仍然能够响应。
BOOL threadProcess1Finished =NO;
-(void)threadProce1{
NSLog(@"Enter threadProce1.");
for (int i=0; i<5;i++) {
NSLog(@"InthreadProce1 count = %d.", i);
sleep(1);
}
threadProcess1Finished =YES;
NSLog(@"Exit threadProce1.");
}
BOOL threadProcess2Finished =NO;
-(void)threadProce2{
NSLog(@"Enter threadProce2.");
for (int i=0; i<5;i++) {
NSLog(@"InthreadProce2 count = %d.", i);
sleep(1);
}
threadProcess2Finished =YES;
NSLog(@"Exit threadProce2.");
}
- (IBAction)buttonNormalThreadTestPressed:(UIButton *)sender {
NSLog(@"EnterbuttonNormalThreadTestPressed");
threadProcess1Finished =NO;
NSLog(@"Start a new thread.");
[NSThreaddetachNewThreadSelector: @selector(threadProce1)
toTarget: self
withObject: nil];
// 通常等待线程处理完后再继续操作的代码如下面的形式。
// 在等待线程threadProce1结束之前，调用buttonTestPressed，界面没有响应，直到threadProce1运行完，才打印buttonTestPressed里面的日志。
while (!threadProcess1Finished) {
[NSThreadsleepForTimeInterval: 0.5];
}
NSLog(@"ExitbuttonNormalThreadTestPressed");
}
- (IBAction)buttonRunloopPressed:(id)sender {
NSLog(@"Enter buttonRunloopPressed");
threadProcess2Finished =NO;
NSLog(@"Start a new thread.");
[NSThreaddetachNewThreadSelector: @selector(threadProce2)
toTarget: self
withObject: nil];
// 使用runloop，情况就不一样了。
// 在等待线程threadProce2结束之前，调用buttonTestPressed，界面立马响应，并打印buttonTestPressed里面的日志。
// 这就是runloop的神奇所在
while (!threadProcess2Finished) {
NSLog(@"Begin runloop");
[[NSRunLoopcurrentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate: [NSDate distantFuture]];
NSLog(@"End runloop.");
}
NSLog(@"Exit buttonRunloopPressed");
}
- (IBAction)buttonTestPressed:(id)sender{
NSLog(@"Enter buttonTestPressed");
NSLog(@"Exit buttonTestPressed");
}
日志信息如下：
2013-04-07 14:25:22.829 Runloop[657:11303] EnterbuttonNormalThreadTestPressed
2013-04-07 14:25:22.830 Runloop[657:11303] Start a new thread.
2013-04-07 14:25:22.831 Runloop[657:1250f] Enter threadProce1.
2013-04-07 14:25:22.832 Runloop[657:1250f] In threadProce1 count = 0.
2013-04-07 14:25:23.833 Runloop[657:1250f] In threadProce1 count = 1.
2013-04-07 14:25:24.834 Runloop[657:1250f] In threadProce1 count = 2.
2013-04-07 14:25:25.835 Runloop[657:1250f] In threadProce1 count = 3.
2013-04-07 14:25:26.837 Runloop[657:1250f] In threadProce1 count = 4.
2013-04-07 14:25:27.839 Runloop[657:1250f] Exit threadProce1.
2013-04-07 14:25:27.840 Runloop[657:11303]ExitbuttonNormalThreadTestPressed
2013-04-07 14:25:27.841 Runloop[657:11303]Enter buttonTestPressed
2013-04-07 14:25:27.842 Runloop[657:11303] Exit buttonTestPressed
2013-04-07 14:25:27.843 Runloop[657:11303] Enter buttonTestPressed
2013-04-07 14:25:27.844 Runloop[657:11303] Exit buttonTestPressed
2013-04-07 14:43:41.790 Runloop[657:11303] Enter buttonRunloopPressed
2013-04-07 14:43:41.790 Runloop[657:11303] Start a new thread.
2013-04-07 14:43:41.791 Runloop[657:11303] Begin runloop
2013-04-07 14:43:41.791 Runloop[657:14f0b] Enter threadProce2.
2013-04-07 14:43:41.792 Runloop[657:14f0b] In threadProce2 count = 0.
2013-04-07 14:43:42.542 Runloop[657:11303] End runloop.
2013-04-07 14:43:42.543 Runloop[657:11303] Begin runloop
2013-04-07 14:43:42.694 Runloop[657:11303]Enter buttonTestPressed
2013-04-07 14:43:42.694 Runloop[657:11303]Exit buttonTestPressed
2013-04-07 14:43:42.695 Runloop[657:11303] End runloop.
2013-04-07 14:43:42.696 Runloop[657:11303] Begin runloop
2013-04-07 14:43:42.793 Runloop[657:14f0b] In threadProce2 count = 1.
2013-04-07 14:43:43.326 Runloop[657:11303] End runloop.
2013-04-07 14:43:43.327 Runloop[657:11303] Begin runloop
2013-04-07 14:43:43.438 Runloop[657:11303]Enter buttonTestPressed
2013-04-07 14:43:43.438 Runloop[657:11303]Exit buttonTestPressed
2013-04-07 14:43:43.439 Runloop[657:11303] End runloop.
2013-04-07 14:43:43.440 Runloop[657:11303] Begin runloop
2013-04-07 14:43:43.795 Runloop[657:14f0b] In threadProce2 count = 2.
2013-04-07 14:43:44.797 Runloop[657:14f0b] In threadProce2 count = 3.
2013-04-07 14:43:45.798 Runloop[657:14f0b] In threadProce2 count = 4.
2013-04-07 14:43:46.800 Runloop[657:14f0b] Exit threadProce2.
三、Runloop简单实例：
- (void)viewDidLoad
{
[superviewDidLoad];
// Doany additional setup after loading the view, typically from a nib.
[NSThreaddetachNewThreadSelector: @selector(newThreadProcess)
toTarget: self
withObject: nil];
}
- (void)newThreadProcess
{
@autoreleasepool {
////获得当前thread的Runloop
NSRunLoop* myRunLoop = [NSRunLoop currentRunLoop];
//设置Run loop observer的运行环境
CFRunLoopObserverContext context = {0,self,NULL,NULL,NULL};
//创建Run loop observer对象
//第一个参数用于分配observer对象的内存
//第二个参数用以设置observer所要关注的事件，详见回调函数myRunLoopObserver中注释
//第三个参数用于标识该observer是在第一次进入runloop时执行还是每次进入run loop处理时均执行
//第四个参数用于设置该observer的优先级
//第五个参数用于设置该observer的回调函数
//第六个参数用于设置该observer的运行环境
CFRunLoopObserverRef observer =CFRunLoopObserverCreate(kCFAllocatorDefault,kCFRunLoopAllActivities, YES, 0, &myRunLoopObserver, &context);
if(observer)
{
//将Cocoa的NSRunLoop类型转换成CoreFoundation的CFRunLoopRef类型
CFRunLoopRef cfRunLoop = [myRunLoop getCFRunLoop];
//将新建的observer加入到当前thread的runloop
CFRunLoopAddObserver(cfRunLoop, observer, kCFRunLoopDefaultMode);
}
//
[NSTimerscheduledTimerWithTimeInterval: 1
target: self
selector:@selector(timerProcess)
userInfo: nil
repeats: YES];
NSInteger loopCount = 2;
do{
//启动当前thread的loop直到所指定的时间到达，在loop运行时，runloop会处理所有来自与该run loop联系的inputsource的数据
//对于本例与当前run loop联系的inputsource只有一个Timer类型的source。
//该Timer每隔1秒发送触发事件给runloop，run loop检测到该事件时会调用相应的处理方法。
//由于在run loop添加了observer且设置observer对所有的runloop行为都感兴趣。
//当调用runUnitDate方法时，observer检测到runloop启动并进入循环，observer会调用其回调函数，第二个参数所传递的行为是kCFRunLoopEntry。
//observer检测到runloop的其它行为并调用回调函数的操作与上面的描述相类似。
[myRunLoop runUntilDate:[NSDate dateWithTimeIntervalSinceNow:5.0]];
//当run loop的运行时间到达时，会退出当前的runloop。observer同样会检测到runloop的退出行为并调用其回调函数，第二个参数所传递的行为是kCFRunLoopExit。
loopCount--;
}while (loopCount);
}
}
void myRunLoopObserver(CFRunLoopObserverRef observer,CFRunLoopActivityactivity,void *info)
{
switch (activity) {
//The entrance of the run loop, beforeentering the event processing loop.
//This activity occurs once for each callto CFRunLoopRun and CFRunLoopRunInMode
case kCFRunLoopEntry:
NSLog(@"run loop entry");
break;
//Inside the event processing loop beforeany timers are processed
case kCFRunLoopBeforeTimers:
NSLog(@"run loop before timers");
break;
//Inside the event processing loop beforeany sources are processed
case kCFRunLoopBeforeSources:
NSLog(@"run loop before sources");
break;
//Inside the event processing loop beforethe run loop sleeps, waiting for a source or timer to fire.
//This activity does not occur ifCFRunLoopRunInMode is called with a timeout of 0 seconds.
//It also does not occur in a particulariteration of the event processing loop if a version 0 source fires
case kCFRunLoopBeforeWaiting:
NSLog(@"run loop before waiting");
break;
//Inside the event processing loop afterthe run loop wakes up, but before processing the event that woke it up.
//This activity occurs only if the run loopdid in fact go to sleep during the current loop
case kCFRunLoopAfterWaiting:
NSLog(@"run loop after waiting");
break;
//The exit of the run loop, after exitingthe event processing loop.
//This activity occurs once for each callto CFRunLoopRun and CFRunLoopRunInMode
case kCFRunLoopExit:
NSLog(@"run loop exit");
break;
/*
A combination of all the precedingstages
case kCFRunLoopAllActivities:
break;
*/
default:
break;
}
}
- (void)timerProcess{
for (int i=0; i<5; i++) {
NSLog(@"In timerProcess count = %d.", i);
sleep(1);
}
}
调试打印信息如下：
2012-12-18 09:51:14.174 Texta[645:14807] run loop entry
2012-12-18 09:51:14.175 Texta[645:14807] run loop before timers
2012-12-18 09:51:14.176 Texta[645:14807] run loop before sources
2012-12-18 09:51:14.177 Texta[645:14807] run loop before waiting
2012-12-18 09:51:15.174 Texta[645:14807] run loop after waiting
2012-12-18 09:51:15.176 Texta[645:14807] In timerProcess count = 0.
2012-12-18 09:51:16.178 Texta[645:14807] In timerProcess count = 1.
2012-12-18 09:51:17.181 Texta[645:14807] In timerProcess count = 2.
2012-12-18 09:51:18.183 Texta[645:14807] In timerProcess count = 3.
2012-12-18 09:51:19.185 Texta[645:14807] In timerProcess count = 4.
2012-12-18 09:51:20.187 Texta[645:14807] run loop exit
2012-12-18 09:51:20.189 Texta[645:14807] run loop entry
2012-12-18 09:51:20.190 Texta[645:14807] run loop before timers
2012-12-18 09:51:20.191 Texta[645:14807] run loop before sources
2012-12-18 09:51:20.191 Texta[645:14807] run loop before waiting
2012-12-18 09:51:21.174 Texta[645:14807] run loop after waiting
2012-12-18 09:51:21.176 Texta[645:14807] In timerProcess count = 0.
2012-12-18 09:51:22.178 Texta[645:14807] In timerProcess count = 1.
2012-12-18 09:51:23.181 Texta[645:14807] In timerProcess count = 2.
2012-12-18 09:51:24.183 Texta[645:14807] In timerProcess count = 3.
2012-12-18 09:51:25.185 Texta[645:14807] In timerProcess count = 4.
2012-12-18 09:51:26.187 Texta[645:14807] run loop exit
四、Runloop可以阻塞线程，等待其他线程执行后再执行。
比如：
BOOL StopFlag =NO;
- (void)viewDidLoad
{
[superviewDidLoad];
// Doany additional setup after loading the view, typically from a nib.
StopFlag =NO;
NSLog(@"Start a new thread.");
[NSThreaddetachNewThreadSelector: @selector(newThreadProc)
toTarget:self
withObject: nil];
while (!StopFlag) {
NSLog(@"Beginrunloop");
[[NSRunLoopcurrentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate: [NSDate distantFuture]];
NSLog(@"Endrunloop.");
}
NSLog(@"OK");
}
-(void)newThreadProc{
NSLog(@"Enter newThreadProc.");
for (int i=0; i<10; i++) {
NSLog(@"InnewThreadProc count = %d.", i);
sleep(1);
}
StopFlag =YES;
NSLog(@"Exit newThreadProc.");
}
}
调试打印信息如下：
2012-12-18 08:50:34.220 Runloop[374:11303] Start a new thread.
2012-12-18 08:50:34.222 Runloop[374:11303] Begin runloop
2012-12-18 08:50:34.222 Runloop[374:14b03] Enter newThreadProc.
2012-12-18 08:50:34.223 Runloop[374:14b03] In newThreadProc count = 0.
2012-12-18 08:50:35.225 Runloop[374:14b03] In newThreadProc count = 1.
2012-12-18 08:50:36.228 Runloop[374:14b03] In newThreadProc count = 2.
2012-12-18 08:50:37.230 Runloop[374:14b03] In newThreadProc count = 3.
2012-12-18 08:50:38.233 Runloop[374:14b03] In newThreadProc count = 4.
2012-12-18 08:50:39.235 Runloop[374:14b03] In newThreadProc count = 5.
2012-12-18 08:50:40.237 Runloop[374:14b03] In newThreadProc count = 6.
2012-12-18 08:50:41.240 Runloop[374:14b03] In newThreadProc count = 7.
2012-12-18 08:50:42.242 Runloop[374:14b03] In newThreadProc count = 8.
2012-12-18 08:50:43.245 Runloop[374:14b03] In newThreadProc count = 9.
2012-12-18 08:50:44.247 Runloop[374:14b03] Exit newThreadProc.
2012-12-18 08:51:00.000 Runloop[374:11303] End runloop.
2012-12-18 08:51:00.001 Runloop[374:11303] OK
从调试打印信息可以看到，while循环后执行的语句会在很长时间后才被执行。因为，改变变量StopFlag的值，runloop对象根本不知道，runloop在这个时候未被唤醒。有其他事件在某个时点唤醒了主线程，这才结束了while循环，但延缓的时长总是不定的。。
将代码稍微修改一下：
[[NSRunLoopcurrentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate: [NSDatedateWithTimeIntervalSinceNow: 1]];
缩短runloop的休眠时间，看起来解决了上面出现的问题。
但这样会导致runloop被经常性的唤醒，违背了runloop的设计初衷。runloop的目的就死让你的线程在有工作的时候忙于工作，而没工作的时候处于休眠状态。
最后，看下下面正确的写法：
BOOL StopFlag =NO;
- (void)viewDidLoad
{
[superviewDidLoad];
// Doany additional setup after loading the view, typically from a nib.
StopFlag =NO;
NSLog(@"Start a new thread.");
[NSThreaddetachNewThreadSelector: @selector(newThreadProc)
toTarget: self
withObject: nil];
while (!StopFlag) {
NSLog(@"Beginrunloop");
[[NSRunLoopcurrentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate: [NSDatedistantFuture]];
NSLog(@"Endrunloop.");
}
NSLog(@"OK");
}
-(void)newThreadProc{
NSLog(@"Enter newThreadProc.");
for (int i=0; i<10; i++) {
NSLog(@"InnewThreadProc count = %d.", i);
sleep(1);
}
[selfperformSelectorOnMainThread: @selector(setEnd)
withObject: nil
waitUntilDone: NO];
NSLog(@"Exit newThreadProc.");
}
-(void)setEnd{
StopFlag = YES;
}
调试打印信息如下：
2012-12-18 09:05:17.161 Runloop[410:11303] Start a new thread.
2012-12-18 09:05:17.163 Runloop[410:14a03] Enter newThreadProc.
2012-12-18 09:05:17.164 Runloop[410:14a03] In newThreadProc count = 0.
2012-12-18 09:05:17.165 Runloop[410:11303] Begin runloop
2012-12-18 09:05:18.166 Runloop[410:14a03] In newThreadProc count = 1.
2012-12-18 09:05:19.168 Runloop[410:14a03] In newThreadProc count = 2.
2012-12-18 09:05:20.171 Runloop[410:14a03] In newThreadProc count = 3.
2012-12-18 09:05:21.173 Runloop[410:14a03] In newThreadProc count = 4.
2012-12-18 09:05:22.175 Runloop[410:14a03] In newThreadProc count = 5.
2012-12-18 09:05:23.178 Runloop[410:14a03] In newThreadProc count = 6.
2012-12-18 09:05:24.180 Runloop[410:14a03] In newThreadProc count = 7.
2012-12-18 09:05:25.182 Runloop[410:14a03] In newThreadProc count = 8.
2012-12-18 09:05:26.185 Runloop[410:14a03] In newThreadProc count = 9.
2012-12-18 09:05:27.188 Runloop[410:14a03] Exit newThreadProc.
2012-12-18 09:05:27.188 Runloop[410:11303] End runloop.
2012-12-18 09:05:27.189 Runloop[410:11303] OK
把直接设置变量，改为向主线程发送消息，唤醒runloop，延时问题解决。
原文出处：http://blog.csdn.net/jjunjoe/article/details/8313016，特别感谢。
原文：http://www.cnblogs.com/hereiam/p/3819926.html