什么是RunLoop?
顾名思义:运行循环,在程序运行过程中循环做一些事情
应用范畴:
·定时器(Timer)、PerformSelector
·GCD Async Main Queue
·事件响应、手势识别、界面刷新
·网络请求
·AutoreleasePool
RunLoop与线程
·每条线程都有唯一的一个与之对应的RunLoop对象
·RunLoop保存在一个全局的Dictionary里,线程作为key,RunLoop作为value
·线程刚创建时并没有RunLoop对象,RunLoop会在第一次获取它时创建
·RunLoop会在线程结束时销毁
·主线程的RunLoop已经自动获取(创建),子线程默认没有开启RunLoop
获取RunLoop对象
Foundation
[NSRunLoop currentRunLoop]; // 获得当前线程的RunLoop对象
[NSRunLoop mainRunLoop]; // 获得主线程的RunLoop对象
Core Foundation
CFRunLoopGetCurrent(); // 获得当前线程的RunLoop对象
CFRunLoopGetMain(); // 获得主线程的RunLoop对象
RunLoop相关的类
Core Foundation中关于RunLoop的5个类
- CFRunLoopRef
- CFRunLoopModeRef
- CFRunLoopSourceRef
- CFRunLoopTimerRef
- CFRunLoopObserverRef
RunLoop底层数据结构
CFRunLoopModeRef
CFRunLoopModeRef代表RunLoop的运行模式
一个RunLoop包含若干个Mode,每个Mode又包含若干个Source0/Source1/Timer/Observer
RunLoop启动时只能选择其中一个Mode,作为currentMode
如果需要切换Mode,只能退出当前Loop,再重新选择一个Mode进入
·不同组的Source0/Source1/Timer/Observer能分隔开来,互不影响如果Mode里没有任何Source0/Source1/Timer/Observer,RunLoop会立马退出
常见的2种Mode
- kCFRunLoopDefaultMode(NSDefaultRunLoopMode):App的默认Mode,通常主线程是在这个Mode下运行
- UITrackingRunLoopMode:界面跟踪 Mode,用于 ScrollView 追踪触摸滑动,保证界面滑动时不受其他 Mode 影响
CFRunLoopObserverRef
/* Run Loop Observer Activities */
typedef CF_OPTIONS(CFOptionFlags, CFRunLoopActivity) {
kCFRunLoopEntry = (1UL << 0), //即将进入Loop
kCFRunLoopBeforeTimers = (1UL << 1), //即将处理Timer
kCFRunLoopBeforeSources = (1UL << 2), //即将处理Source
kCFRunLoopBeforeWaiting = (1UL << 5), //即将进入休眠
kCFRunLoopAfterWaiting = (1UL << 6), //刚从休眠中唤醒
kCFRunLoopExit = (1UL << 7), //即将退出Loop
kCFRunLoopAllActivities = 0x0FFFFFFFU
};
添加Observer监听RunLoop的所有状态
// 创建Observer
CFRunLoopObserverRef observer = CFRunLoopObserverCreateWithHandler(kCFAllocatorDefault, kCFRunLoopAllActivities, YES, 0, ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
switch (activity) {
case kCFRunLoopEntry:
NSLog(@"kCFRunLoopEntry");
break;
case kCFRunLoopBeforeTimers:
NSLog(@"kCFRunLoopBeforeTimers");
break;
case kCFRunLoopBeforeSources:
NSLog(@"kCFRunLoopBeforeSources");
break;
case kCFRunLoopBeforeWaiting:
NSLog(@"kCFRunLoopBeforeWaiting");
break;
case kCFRunLoopAfterWaiting:
NSLog(@"kCFRunLoopAfterWaiting");
break;
case kCFRunLoopExit:
NSLog(@"kCFRunLoopExit");
break;
default:
break;
}
});
// 添加Observer到RunLoop中
CFRunLoopAddObserver(CFRunLoopGetCurrent(), observer, kCFRunLoopCommonModes);
// 释放
CFRelease(observer);
RunLoop的运行逻辑
底层源码的主要逻辑
// RunLoop入口
SInt32 CFRunLoopRunSpecific(CFRunLoopRef rl, CFStringRef modeName, CFTimeInterval seconds, Boolean returnAfterSourceHandled) { /* DOES CALLOUT */
int32_t result = kCFRunLoopRunFinished;
// 通知Observers: 进入Loop
if (currentMode->_observerMask & kCFRunLoopEntry ) __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopEntry);
// 具体要做的事情
result = __CFRunLoopRun(rl, currentMode, seconds, returnAfterSourceHandled, previousMode);
// 通知Observers: 退出Loop
if (currentMode->_observerMask & kCFRunLoopExit ) __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit);
return result;
}
// RunLoop主要逻辑
static int32_t __CFRunLoopRun(CFRunLoopRef rl, CFRunLoopModeRef rlm, CFTimeInterval seconds, Boolean stopAfterHandle, CFRunLoopModeRef previousMode) {
uint64_t startTSR = mach_absolute_time();
do {
// 通知Observer:即将处理Timers
if (rlm->_observerMask & kCFRunLoopBeforeTimers) __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeTimers);
// 通知Observer:即将处理Sources
if (rlm->_observerMask & kCFRunLoopBeforeSources) __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeSources);
// 处理Blocks
__CFRunLoopDoBlocks(rl, rlm);
// 处理Source0
Boolean sourceHandledThisLoop = __CFRunLoopDoSources0(rl, rlm, stopAfterHandle);
if (sourceHandledThisLoop) {
// 处理Blocks
__CFRunLoopDoBlocks(rl, rlm);
}
// 判断有无Source1
if (__CFRunLoopServiceMachPort(dispatchPort, &msg, sizeof(msg_buffer), &livePort, 0, &voucherState, NULL)) {
// 如果有Source1,就跳转到handel_msg
goto handle_msg;
}
// 通知Observers:即将休眠
if (!poll && (rlm->_observerMask & kCFRunLoopBeforeWaiting)) __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeWaiting);
__CFRunLoopSetSleeping(rl);
// 等待别的消息来唤醒当前线程
__CFRunLoopServiceMachPort(waitSet, &msg, sizeof(msg_buffer), &livePort, poll ? 0 : TIMEOUT_INFINITY, &voucherState, &voucherCopy);
// 通知Observer:结束休眠
__CFRunLoopUnsetSleeping(rl);
if (!poll && (rlm->_observerMask & kCFRunLoopAfterWaiting)) __CFRunLoopDoObservers(rl, rlm, kCFRunLoopAfterWaiting);
handle_msg:;
__CFRunLoopSetIgnoreWakeUps(rl);
if (rlm->_timerPort != MACH_PORT_NULL && livePort == rlm->_timerPort) {
// 被Timer唤醒了
CFRUNLOOP_WAKEUP_FOR_TIMER();
// 处理Timers
if (!__CFRunLoopDoTimers(rl, rlm, mach_absolute_time())) {
// Re-arm the next timer
__CFArmNextTimerInMode(rlm, rl);
}
} else if (livePort == dispatchPort) {
// 被GCD唤醒
CFRUNLOOP_WAKEUP_FOR_DISPATCH();
// 处理GCD
__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__(msg);
} else {
//被Source1唤醒
CFRUNLOOP_WAKEUP_FOR_SOURCE();
// 处理Source1
sourceHandledThisLoop = __CFRunLoopDoSource1(rl, rlm, rls, msg, msg->msgh_size, &reply) || sourceHandledThisLoop;
}
// 处理Blocks
__CFRunLoopDoBlocks(rl, rlm);
//设置返回值
if (sourceHandledThisLoop && stopAfterHandle) {
retVal = kCFRunLoopRunHandledSource;
} else if (timeout_context->termTSR < mach_absolute_time()) {
retVal = kCFRunLoopRunTimedOut;
} else if (__CFRunLoopIsStopped(rl)) {
__CFRunLoopUnsetStopped(rl);
retVal = kCFRunLoopRunStopped;
} else if (rlm->_stopped) {
rlm->_stopped = false;
retVal = kCFRunLoopRunStopped;
} else if (__CFRunLoopModeIsEmpty(rl, rlm, previousMode)) {
retVal = kCFRunLoopRunFinished;
}
} while (0 == retVal);
return retVal;
}
RunLoop在实际中的应用
- 解决NSTimer在滑动时停止工作的问题
问题:页面滑动时,RunLoop会切换到UITrackingRunLoopMode,timer会停止。
解决办法:
将timer 添加到当前RunLoop,使用CommonModes
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes]
注意:
NSDefaultRunLoopMode、UITrackingRunLoopMode才是真正的存在模式
NSRunLoopCommonModes并不是一个真的模式,它只是一个标记
timer能在_commonModes数组中存在的模式下工作
- 控制线程生命周期(线程保活)
AFNetworking就是创建了子线程,然后让子线程一直存在于后台,方便进行一些子线程的任务,减少线程创建销毁的开销,提高性能
@interface ViewController ()
@property (strong, nonatomic) NSThread *thread;
@property (assign, nonatomic, getter=isStoped) BOOL stopped;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
__weak typeof(self) weakSelf = self;
self.stopped = NO;
self.thread = [[NSThread alloc] initWithBlock:^{
NSLog(@"%@----begin----", [NSThread currentThread]);
// 往RunLoop里面添加Source\Timer\Observer
[[NSRunLoop currentRunLoop] addPort:[[NSPort alloc] init] forMode:NSDefaultRunLoopMode];
while (weakSelf && !weakSelf.isStoped) {
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
}
/*
it runs the receiver in the NSDefaultRunLoopMode by repeatedly invoking runMode:beforeDate:.
In other words, this method effectively begins an infinite loop that processes data from the run loop’s input sources and timers
*/
// [[NSRunLoop currentRunLoop] run];
// NSRunLoop的run方法是无法停止的,它专门用于开启一个永不销毁的线程(NSRunLoop)
NSLog(@"%@----end----", [NSThread currentThread]);
}];
[self.thread start];
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
if (!self.thread) return;
[self performSelector:@selector(test) onThread:self.thread withObject:nil waitUntilDone:NO];
}
// 子线程需要执行的任务
- (void)test
{
NSLog(@"%s %@", __func__, [NSThread currentThread]);
}
- (void)stop {
if (!self.thread) return;
// 在子线程调用stop(waitUntilDone设置为YES,代表子线程的代码执行完毕后,这个方法才会往下走)
[self performSelector:@selector(stopThread) onThread:self.thread withObject:nil waitUntilDone:YES];
}
// 用于停止子线程的RunLoop
- (void)stopThread
{
// 设置标记为YES
self.stopped = YES;
// 停止RunLoop
CFRunLoopStop(CFRunLoopGetCurrent());
NSLog(@"%s %@", __func__, [NSThread currentThread]);
// 清空线程
self.thread = nil;
}
- (void)dealloc
{
NSLog(@"%s", __func__);
[self stop];
}
- 监控应用卡顿
- 性能优化
面试题
1.runloop的内部实用逻辑?
RunLoop的运行逻辑图.png
2.runloop是怎么响应用户的操作的,具体流程是怎么样的?
以屏幕点击为例, Source1捕捉系统事件,将事件包装成事件队列(EventQueue),事件队列是在Source0中处理的(Source1捕捉,Source0处理)