RunLoop - 符琼林的个人博客

RunLoop初识

RunLoop是什么？

字面意思：运行循环
程序运行过程中循环的处理事情
实际是一个对象，这个对象提供一个入口函数，执行这个入口函数后，程序会进入一个do..while循环，循环的处理一些事情。

RunLoop有什么用？

如果没有Runloop?

int main(int argc, char * argv[]){
   
@autoreleasepool { 
  
    NSLog(@“%s”, __func__);
}
return 0;
}
//结果：程序执行完就会退出。

如果有RunLoop？

int main(int argc, char * argv[]){
   
@autoreleasepool { 
  
    return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]))
  
    }
}
//结果：程序一直执行没有退出

RunLoop有什么用？
- 保持程序的持续运行
- 处理App中的各种事件（触摸、定时器、PerformSelector）
- 节省CPU资源、提高程序性能：该做事的时候做事，该休息的时候休息。

RunLoop怎么使用？

iOS提供了2套API来访问和使用RunLoop：

//NSRunLoop基于CFRunLoopRef封装
  Foundation：NSRunLoop
Core Foundation：CFRunLoopRef

CFRunLoopRef是开源的

RunLoop与线程

线程与RunLoop是一一对应的
线程创建的时候，并没有创建RunLoop对象，RunLoop会在第一次获取的时候自动创建

主线程默认开启了RunLoop, 子线程默认没有开启子线程

static CFMutableDictionaryRef __CFRunLoops = NULL;
static CFLock_t loopsLock = CFLockInit;
  
// should only be called by Foundation
// t==0 is a synonym for "main thread" that always works
CF_EXPORT CFRunLoopRef _CFRunLoopGet0(pthread_t t) {
   //__CFRunLoops全局字典
    if (!__CFRunLoops) {
        __CFUnlock(&loopsLock);
        //创建字典并且创建主runloop
        CFMutableDictionaryRef dict = CFDictionaryCreateMutable(kCFAllocatorSystemDefault, 0, NULL, &kCFTypeDictionaryValueCallBacks);
        CFRunLoopRef mainLoop = __CFRunLoopCreate(pthread_main_thread_np());
        //线程为key runloop为值存进去
        CFDictionarySetValue(dict, pthreadPointer(pthread_main_thread_np()), mainLoop);
          
    }
    //去runloop
    CFRunLoopRef loop = (CFRunLoopRef)CFDictionaryGetValue(__CFRunLoops, pthreadPointer(t));
    __CFUnlock(&loopsLock);
    if (!loop) {
        //没有取到就创建
        CFRunLoopRef newLoop = __CFRunLoopCreate(t);
        __CFLock(&loopsLock);
        loop = (CFRunLoopRef)CFDictionaryGetValue(__CFRunLoops, pthreadPointer(t));
        if (!loop) {
            CFDictionarySetValue(__CFRunLoops, pthreadPointer(t), newLoop);
            loop = newLoop;
        }
     
    return loop;
}

RunLoop相关类

CFRunLoopRef
CFRunLoopModeRef
CFRunLoopSourceRef
CFRunLoopTimerRef
CFRunLoopObserverRef

CFRunLoopRef

一个RunLoop对应着一条线程
一个RunLoop包含多个Mode，每个 Mode 又包含若干个 Source/Timer/Observer
Source/Timer/Observer又叫mode item。不同mode下的mode item互不影响
RunLoop运行过程中，只选择一种模式运行
切换Mode，程序退出当前RunLoop mode，再重新指定Mode执行

CFRunLoopModeRef

struct __CFRunLoopMode {
    CFRuntimeBase _base;
    pthread_mutex_t _lock;	/* must have the run loop locked before locking this */
    CFStringRef _name;
    Boolean _stopped;
    char _padding[3];
    CFMutableSetRef _sources0;
    CFMutableSetRef _sources1;
    CFMutableArrayRef _observers;
    CFMutableArrayRef _timers;
    CFMutableDictionaryRef _portToV1SourceMap;
    __CFPortSet _portSet;
    CFIndex _observerMask;
#if USE_DISPATCH_SOURCE_FOR_TIMERS
    dispatch_source_t _timerSource;
    dispatch_queue_t _queue;
    Boolean _timerFired; // set to true by the source when a timer has fired
    Boolean _dispatchTimerArmed;
#endif
#if USE_MK_TIMER_TOO
    mach_port_t _timerPort;
    Boolean _mkTimerArmed;
#endif
#if DEPLOYMENT_TARGET_WINDOWS
    DWORD _msgQMask;
    void (*_msgPump)(void);
#endif
    uint64_t _timerSoftDeadline; /* TSR */
    uint64_t _timerHardDeadline; /* TSR */
};

//获取当前模式
CFRunLoopRef rl = CFRunLoopGetCurrent();
CFRunLoopMode mode = CFRunLoopCopyCurrentMode(rl);
NSLog(@"mode ---> %@", mode);
//获取全部模式
CFArrayRef array = CFRunLoopCopyAllModes(rl);
NSLog(@"array ---> %@", array);

/*
    UITrackingRunLoopMode,//界面跟着，主要用于scrollview滑动，会自动切换
    GSEventReceiveRunLoopMode,//接受系统事件
    kCFRunLoopDefaultMode,
    kCFRunLoopCommonModes//公用属性items
*/

CFRunLoopSourceRef

//源分为source0和source1
//source0需要我们标志为待处理的状态，并且唤醒runloop
//source1系统标志为待处理的状态，并且已经唤醒runloop
//能自定义的也就是source0
struct __CFRunLoopSource {
    CFRuntimeBase _base;
    uint32_t _bits;//标志
    pthread_mutex_t _lock;
    CFIndex _order;			/* immutable */
    CFMutableBagRef _runLoops;
    //联合体，节省内存
    union {
	CFRunLoopSourceContext version0;	/* immutable, except invalidation */
        CFRunLoopSourceContext1 version1;	/* immutable, except invalidation */
    } _context;
};

//示例
- (void) sourceTest {
    CFRunLoopSourceContext context = {
        0,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        schedule,
        cancel,
        perform
    };
    
    CFRunLoopSourceRef source0 = CFRunLoopSourceCreate(CFAllocatorGetDefault(), 0, &context);
    //触发schedule
    CFRunLoopAddSource(CFRunLoopGetCurrent(), source0, kCFRunLoopDefaultMode);
    //触发perform，标识为待处理
    CFRunLoopSourceSignal(source0);
    CFRunLoopWakeUp(CFRunLoopGetCurrent());
    //触发cancel
    CFRunLoopRemoveSource(CFRunLoopGetCurrent(), source0, kCFRunLoopDefaultMode);
    CFRelease(source0);
}

void schedule(void *info, CFRunLoopRef rl, CFRunLoopMode mode) {
    NSLog(@"%s", __func__);
}

void cancel(void *info, CFRunLoopRef rl, CFRunLoopMode mode) {
    NSLog(@"%s", __func__);
}

void perform(void *info) {
    NSLog(@"%s", __func__);
}


source0
触摸事件
自定义输入源
performSelector:onThread:

source1
端口(Port)

计时源
NSTimer
performSelector:withObject:afterDelay

NSPort

NSPort是什么?
- 通信通道的抽象类。
能干什么?
- 我们能够使用端口进行线程间的一个通信。
要接收传入消息，必须将NSPort对象添加到NSRunLoop对象中作为输入源
端口用完之后，如果不用，要释放，不然产生的端口对象可能会逗留并创建内存泄漏。要使端口对象无效，请调用它的invalidate方法。
Foundation定义了NSPort的三个具体子类。NSMachPort和NSMessagePort只允许本地(在同一台机器上)通信。NSSocketPort支持本地和远程通信，但是对于本地情况，可能比其他的要昂贵。

在使用allocWithZone:或port创建NSPort对象时，将创建一个NSMachPort对象。

  @interface ViewController () 
    
  @property (nonatomic, strong) NSPort* subThreadPort;
  @property (nonatomic, strong) NSPort* mainThreadPort;
    
  @end
    
  @implementation ViewController
    
  - (void)viewDidLoad {
      [super viewDidLoad];
        
      self.mainThreadPort = [NSPort port];
      self.mainThreadPort.delegate = self;
      [[NSRunLoop currentRunLoop] addPort:self.mainThreadPort forMode:NSDefaultRunLoopMode];
      [self task];
  }
    
  - (void) task {
      NSThread* thread = [[NSThread alloc] initWithBlock:^{
          self.subThreadPort = [NSPort port];
          self.subThreadPort.delegate = self;
            
          [[NSRunLoop currentRunLoop] addPort:self.subThreadPort forMode:NSDefaultRunLoopMode];
          [[NSRunLoop currentRunLoop] run];
      }];
      [thread setName:@"子线程"];
      [thread start];
  }
    
  - (void)handlePortMessage:(id)message {
      NSLog(@"%@", [NSThread currentThread]);
        
      NSMutableArray* components = [message valueForKey:@"components"];
        
      if ([components count] > 0) {
          NSData* data = [components objectAtIndex:0];
          NSString* str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
          NSLog(@"%@", str);
      }
        
      sleep(2);
      if (![[NSThread currentThread] isMainThread]) {
          NSMutableArray* sendComponents = [NSMutableArray array];
          NSData* data = [@"world" dataUsingEncoding:NSUTF8StringEncoding];
          [sendComponents addObject:data];
           [self.mainThreadPort sendBeforeDate:[NSDate date] components:sendComponents from:self.subThreadPort reserved:0];
      }
  }
    
  - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
        
      NSMutableArray* components = [NSMutableArray array];
      NSData* data = [@"hello" dataUsingEncoding:NSUTF8StringEncoding];
      [components addObject:data];
      //端口传递的都是NSData
      [self.subThreadPort sendBeforeDate:[NSDate date] components:components from:self.mainThreadPort reserved:0];
  }
  @end

CFRunLoopTimerRef

- (void) timerTest {
   CFRunLoopTimerRef timer =  CFRunLoopTimerCreateWithHandler(kCFAllocatorDefault, 0, 1, 0, 0, ^(CFRunLoopTimerRef timer) {
       NSLog(@"%s", __func__);
    });
    CFRunLoopAddTimer(CFRunLoopGetCurrent(), timer, kCFRunLoopDefaultMode);
}

CFRunLoopObserverRef

观察者（observer）：监听RunLoop的状态

- (void) observerTest {
    CFRunLoopObserverRef observer = CFRunLoopObserverCreateWithHandler(kCFAllocatorDefault, kCFRunLoopAllActivities, YES, 0, ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
        NSLog(@"%lu", activity);
    });
    CFRunLoopAddObserver(CFRunLoopGetCurrent(), observer, kCFRunLoopDefaultMode);
}

RunLoop内部执行过程

SInt32 CFRunLoopRunSpecific(CFRunLoopRef rl, CFStringRef modeName, CFTimeInterval seconds, Boolean returnAfterSourceHandled) {     /* DOES CALLOUT */
    CHECK_FOR_FORK();
    if (__CFRunLoopIsDeallocating(rl)) return kCFRunLoopRunFinished;
    __CFRunLoopLock(rl);
    
    /// 首先根据modeName找到对应mode
    CFRunLoopModeRef currentMode = __CFRunLoopFindMode(rl, modeName, false);
    
    
    /// 通知 Observers: RunLoop 即将进入 loop。
    __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopEntry);
    
    /// 内部函数，进入loop
    result = __CFRunLoopRun(rl, currentMode, seconds, returnAfterSourceHandled, previousMode);
    
    /// 通知 Observers: RunLoop 即将退出。
    __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit);
    
    return result;
}

/// 核心函数
static int32_t __CFRunLoopRun(CFRunLoopRef rl, CFRunLoopModeRef rlm, CFTimeInterval seconds, Boolean stopAfterHandle, CFRunLoopModeRef previousMode) {
    
    int32_t retVal = 0;
    do {
        
        /// 通知 Observers: 即将处理timer事件
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeTimers);
        
        /// 通知 Observers: 即将处理Source事件
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeSources)
        
        /// 处理Blocks
        __CFRunLoopDoBlocks(rl, rlm);
        
        /// 处理sources0
        Boolean sourceHandledThisLoop = __CFRunLoopDoSources0(rl, rlm, stopAfterHandle);
        
        /// 处理sources0返回为YES
        if (sourceHandledThisLoop) {
            /// 处理Blocks
            __CFRunLoopDoBlocks(rl, rlm);
        }
        
        
        /// 判断有无端口消息(Source1)
        if (__CFRunLoopServiceMachPort(dispatchPort, &msg, sizeof(msg_buffer), &livePort, 0, &voucherState, NULL)) {
            /// 处理消息
            goto handle_msg;
        }
        
        /// 通知 Observers: 即将进入休眠
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeWaiting);
        __CFRunLoopSetSleeping(rl);
        
        /// 等待被唤醒
        __CFRunLoopServiceMachPort(waitSet, &msg, sizeof(msg_buffer), &livePort, poll ? 0 : TIMEOUT_INFINITY, &voucherState, &voucherCopy);
        
        
        // user callouts now OK again
        __CFRunLoopUnsetSleeping(rl);
        
        /// 通知 Observers: 被唤醒，结束休眠
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopAfterWaiting);
        
    handle_msg:
        if (被Timer唤醒) {
            /// 处理Timers
            __CFRunLoopDoTimers(rl, rlm, mach_absolute_time())；
        } else if (被GCD唤醒) {
            /// 处理gcd
            __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__(msg);
        } else if (被Source1唤醒) {
            /// 被Source1唤醒，处理Source1
            __CFRunLoopDoSource1(rl, rlm, rls, msg, msg->msgh_size, &reply)
        }
        
        /// 处理block
        __CFRunLoopDoBlocks(rl, rlm);
        
        
        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;
}

// main  dispatch queue
__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__

// __CFRunLoopDoObservers
__CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__

// __CFRunLoopDoBlocks
__CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__

// __CFRunLoopDoSources0
__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__

// __CFRunLoopDoSource1
__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__

// __CFRunLoopDoTimers
__CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__

休眠的原理

内核：进程、线程
RunLoop实现休眠的原理, 真正的原因是：
- 调用了内核的API(mach_msg), 进入内核态，由内核来将线程置于休眠
- 有消息，就唤醒线程，回到用户态，来处理消息.

应用与总结

定时器

scrollView冲突问题

[NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
        NSLog(@"hello");
}];
  
NSTimer* timer = [NSTimer timerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
        NSLog(@"hello %@", [[NSRunLoop currentRunLoop] currentMode]);
}];
  
//加入运行循环
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
  
//放入子线程
NSThread* th = [[NSThread alloc] initWithBlock:^{
       NSTimer* timer =  [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
            NSLog(@"hello");
        }];
        //线程保活
        [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
        [[NSRunLoop currentRunLoop] run];
          
    }];
[th start];

定时器

NSTimer不准时的原因，主要有2个：
- RunLoop循环处理的这个时间
- 受RunLoop模式的影响

gcd timer与NSTimer是不同的:

都是源，一个是RunLoop的源，一个Dispatch的源
GCD timer不需要加入mode

  @interface ViewController ()
  @property (nonatomic, strong) dispatch_source_t timer;
  @end
      
  @implementation ViewController
      
  - (void)viewDidLoad {
      [super viewDidLoad];
      [self gcdTimerTest];
  }
      
  - (void) gcdTimerTest {
      // 主队列。交由主线程处理。如果runloop任务繁重。受影响
      dispatch_queue_t queue = dispatch_get_main_queue();
      //子线程。跟runloop没有关系
  //    dispatch_queue_t queue = dispatch_queue_create("timer_serial_label", DISPATCH_QUEUE_SERIAL);
      // 创建定时器
      dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
      // 设置定时的开始时间、间隔时间
      dispatch_source_set_timer(timer, dispatch_time(DISPATCH_TIME_NOW, 0), 1*NSEC_PER_SEC, 0);
      // 设置定时器回调
      dispatch_source_set_event_handler(timer, ^{
          NSLog(@"你好");
              
  //        [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
  //            NSLog(@"hello");
  //        }];
      });
      // 启动定时器，默认是关闭的
      dispatch_resume(timer);
      //生命周期不受runloop影响。延长生命周期
      self.timer = timer;
  }
  @end

GCDTimer总结：
- GCDTimer精度高
- GCDTimer主线程执行会RunLoop影响，子线程不受影响
- GCDTimer不受模式切换的影响