RunLoop学习笔记,从CF层面了解由于CFRunLoopMode机制iOS程序ScrollView的滑动为何如此平滑的原因。还有介绍AFNetworking如何单独发起一个global thread内置runloop达到不占用主线程又不耗CPU资源的。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
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。 CFRunLoopModeRunLoop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。
//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]; CFRunLoopTimerNSTimer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
CFRunLoopObserverCocoa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;
} 除非注明,均为Starming星光社原创,转载请注明本文地址:http://www./index.php?v=index&view=74 |
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