简介
简单的说run loop是事件驱动的一个大循环，如下代码所示
int main(int argc, char * argv[]) {
//程序一直运行状态
while (AppIsRunning) {
//睡眠状态，等待唤醒事件
id whoWakesMe = SleepForWakingUp();
//得到唤醒事件
id event = GetEvent(whoWakesMe);
//开始处理事件
HandleEvent(event);
}
return 0;
}
Cocoa会涉及到Run Loops的
- 系统级：GCD，mach kernel，block，pthread
- 应用层：NSTimer，UIEvent，Autorelease，NSObject(NSDelayedPerforming)，NSObject(NSThreadPerformAddition)，CADisplayLink，CATransition，CAAnimation，dispatch_get_main_queue()（GCD中dispatch到main queue的block会被dispatch到main RunLoop执行），NSPort，NSURLConnection，AFNetworking(这个第三方网络请求框架使用在开启新线程中添加自己的run loop监听事件)
在Main thread堆栈中所处位置
堆栈最底层是start(dyld)，往上依次是main，UIApplication(main.m) -> GSEventRunModal(Graphic Services) -> RunLoop(包含CFRunLoopRunSpecific，__CFRunLoopRun，__CFRunLoopDoSouces0，CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION) -> Handle Touch Event
RunLoop原理
CFRunLoop开源代码：http://opensource.apple.com/source/CF/CF-855.17/
执行顺序的伪代码
SetupThisRunLoopRunTimeoutTimer(); // by GCD timer
do {
__CFRunLoopDoObservers(kCFRunLoopBeforeTimers);
__CFRunLoopDoObservers(kCFRunLoopBeforeSources);
__CFRunLoopDoBlocks();
__CFRunLoopDoSource0();
CheckIfExistMessagesInMainDispatchQueue(); // GCD
__CFRunLoopDoObservers(kCFRunLoopBeforeWaiting);
var wakeUpPort = SleepAndWaitForWakingUpPorts();
// mach_msg_trap
// Zzz...
// Received mach_msg, wake up
__CFRunLoopDoObservers(kCFRunLoopAfterWaiting);
// Handle msgs
if (wakeUpPort == timerPort) {
__CFRunLoopDoTimers();
} else if (wakeUpPort == mainDispatchQueuePort) {
// GCD
__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__()
} else {
__CFRunLoopDoSource1();
}
__CFRunLoopDoBlocks();
} while (!stop && !timeout);
构成
Thread包含一个CFRunLoop，一个CFRunLoop包含一种CFRunLoopMode，mode包含CFRunLoopSource，CFRunLoopTimer和CFRunLoopObserver。
CFRunLoopMode
RunLoop只能运行在一种mode下，如果要换mode当前的loop也需要停下重启成新的。利用这个机制，ScrollView过程中NSDefaultRunLoopMode的mode会切换UITrackingRunLoopMode来保证ScrollView的流畅滑动不受只能在NSDefaultRunLoopMode时处理的事件影响滑动。同时mode还是可定制的。
- NSDefaultRunLoopMode：默认，空闲状态
- UITrackingRunLoopMode：ScrollView滑动时
- UIInitializationRunLoopMode：启动时
- NSRunLoopCommonModes：Mode集合
Timer计时会被scrollView的滑动影响的问题可以通过将timer添加到NSRunLoopCommonModes来解决
//将timer添加到NSDefaultRunLoopMode中
[NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:@selector(timerTick:)
userInfo:nil
repeats:YES];
//然后再添加到NSRunLoopCommonModes里
NSTimer *timer = [NSTimer timerWithTimeInterval:1.0
target:self
selector:@selector(timerTick:)
userInfo:nil
repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
CFRunLoopTimer
NSTimer是对RunLoopTimer的封装
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)ti invocation:(NSInvocation *)invocation repeats:(BOOL)yesOrNo;
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti invocation:(NSInvocation *)invocation repeats:(BOOL)yesOrNo;
- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay inModes:(NSArray *)modes;
+ (CADisplayLink *)displayLinkWithTarget:(id)target selector:(SEL)sel;
- (void)addToRunLoop:(NSRunLoop *)runloop forMode:(NSString *)mode;
CFRunLoopSource
- source0：处理如UIEvent，CFSocket这样的事件
- source1：Mach port驱动，CFMachport，CFMessagePort
CFRunLoopObserver
Cocoa框架中很多机制比如CAAnimation等都是由RunLoopObserver触发的。observer到当前状态的变化进行通知。
typedef CF_OPTIONS(CFOptionFlags, CFRunLoopActivity) {
kCFRunLoopEntry = (1UL << 0),
kCFRunLoopBeforeTimers = (1UL << 1),
kCFRunLoopBeforeSources = (1UL << 2),
kCFRunLoopBeforeWaiting = (1UL << 5),
kCFRunLoopAfterWaiting = (1UL << 6),
kCFRunLoopExit = (1UL << 7),
kCFRunLoopAllActivities = 0x0FFFFFFFU
};
使用RunLoop的案例
AFNetworking
使用NSOperation+NSURLConnection并发模型都会面临NSURLConnection下载完成前线程退出导致NSOperation对象接收不到回调的问题。AFNetWorking解决这个问题的方法是按照官方的guidhttps://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSURLConnection_Class/Reference/Reference.html#//apple_ref/occ/instm/NSURLConnection/initWithRequest:delegate:startImmediately:上写的NSURLConnection的delegate方法需要在connection发起的线程runloop中调用，于是AFNetWorking直接借鉴了Apple自己的一个Demohttps://developer.apple.com/LIBRARY/IOS/samplecode/MVCNetworking/Introduction/Intro.html的实现方法单独起一个global thread，内置一个runloop，所有的connection都由这个runloop发起，回调也是它接收，不占用主线程，也不耗CPU资源。
+ (void)networkRequestThreadEntryPoint:(id)__unused object {
@autoreleasepool {
[[NSThread currentThread] setName:@"AFNetworking"];
NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
[runLoop addPort:[NSMachPort port] forMode:NSDefaultRunLoopMode];
[runLoop run];
}
}
+ (NSThread *)networkRequestThread {
static NSThread *_networkRequestThread = nil;
static dispatch_once_t oncePredicate;
dispatch_once(&oncePredicate, ^{
_networkRequestThread =
[[NSThread alloc] initWithTarget:self
selector:@selector(networkRequestThreadEntryPoint:)
object:nil];
[_networkRequestThread start];
});
return _networkRequestThread;
}
类似的可以用这个方法创建一个常驻服务的线程。
TableView中实现平滑滚动延迟加载图片
利用CFRunLoopMode的特性，可以将图片的加载放到NSDefaultRunLoopMode的mode里，这样在滚动UITrackingRunLoopMode这个mode时不会被加载而影响到。
UIImage *downloadedImage = ...;
[self.avatarImageView performSelector:@selector(setImage:)
withObject:downloadedImage
afterDelay:0
inModes:@[NSDefaultRunLoopMode]];
接到程序崩溃时的信号进行自主处理例如弹出提示等
CFRunLoopRef runLoop = CFRunLoopGetCurrent();
NSArray *allModes = CFBridgingRelease(CFRunLoopCopyAllModes(runLoop));
while (1) {
for (NSString *mode in allModes) {
CFRunLoopRunInMode((CFStringRef)mode, 0.001, false);
}
}
异步测试
- (BOOL)runUntilBlock:(BOOL(^)())block timeout:(NSTimeInterval)timeout
{
__block Boolean fulfilled = NO;
void (^beforeWaiting) (CFRunLoopObserverRef observer, CFRunLoopActivity activity) =
^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
fulfilled = block();
if (fulfilled) {
CFRunLoopStop(CFRunLoopGetCurrent());
}
};
CFRunLoopObserverRef observer = CFRunLoopObserverCreateWithHandler(NULL, kCFRunLoopBeforeWaiting, true, 0, beforeWaiting);
CFRunLoopAddObserver(CFRunLoopGetCurrent(), observer, kCFRunLoopDefaultMode);
// Run!
CFRunLoopRunInMode(kCFRunLoopDefaultMode, timeout, false);
CFRunLoopRemoveObserver(CFRunLoopGetCurrent(), observer, kCFRunLoopDefaultMode);
CFRelease(observer);
return fulfilled;
}
