RunLoop源码分析

分析使用的RunLoop源码版本: CF-1153.18.tar
官方示例使用讲解: 链接地址

RunLoop 是什么？

一般来讲，一个线程一次只能执行一个任务，执行完成后线程就会退出。如果我们需要一个机制，让线程能随时处理事件但并不退出，通常的代码逻辑是这样的：

function loop() {
    initialize();
    do {
        var message = get_next_message();
        process_message(message);
    } while (message != quit);
}

这种模型通常被称作 Event Loop。 Event Loop 在很多系统和框架里都有实现，比如 Node.js 的事件处理，比如 Windows 程序的消息循环，再比如 OSX/iOS 里的 RunLoop。实现这种模型的关键点在于：如何管理事件/消息，如何让线程在没有处理消息时休眠以避免资源占用、在有消息到来时立刻被唤醒。

所以，RunLoop 实际上就是一个对象，这个对象管理了其需要处理的事件和消息，并提供了一个入口函数来执行上面 Event Loop 的逻辑。线程执行了这个函数后，就会一直处于这个函数内部 “接受消息->等待->处理” 的循环中，直到这个循环结束（比如传入 quit 的消息），函数返回。

OSX/iOS 系统中，提供了两个这样的对象：NSRunLoop 和 CFRunLoopRef。
CFRunLoopRef 是在 CoreFoundation 框架内的，它提供了纯 C 函数的 API，所有这些 API 都是线程安全的。
NSRunLoop 是基于 CFRunLoopRef 的封装，提供了面向对象的 API，但是这些 API 不是线程安全的。

如何创建 RunLoop

苹果并未提供创建RunLoop的方式，而是通过线程来获取。

[NSRunLoop mainRunLoop]
[NSRunLoop currentRunLoop]

对应到源码分别是获取主线程的CFRunLoopGetMain() 和 获取当前线程的CFRunLoopGetCurrent()。对应的源码为。

CFRunLoopRef CFRunLoopGetMain(void) {
    CHECK_FOR_FORK();
    static CFRunLoopRef __main = NULL; // no retain needed
    if (!__main) __main = _CFRunLoopGet0(pthread_main_thread_np()); // no CAS needed
    return __main;
}

CFRunLoopRef CFRunLoopGetCurrent(void) {
    CHECK_FOR_FORK();
    CFRunLoopRef rl = (CFRunLoopRef)_CFGetTSD(__CFTSDKeyRunLoop);
    if (rl) return rl;
    return _CFRunLoopGet0(pthread_self());
}

通过代码可以发现，获取主线程的 RunLoop 是通过静态变量保存的，且为懒加载，需要时才被创建。获取子线程 RunLoop 先从 Map 中获取，如果没有获取到，创建一个，并将其放入 Map 中。接下来看一下创建的函数_CFRunLoopGet0。

// 删除了部分不重要代码
CF_EXPORT CFRunLoopRef _CFRunLoopGet0(pthread_t t) {

    if (!__CFRunLoops) {
        // 第一次获取 Runloop 时，创建全局 Map
        CFMutableDictionaryRef dict = CFDictionaryCreateMutable(kCFAllocatorSystemDefault, 0, NULL, &kCFTypeDictionaryValueCallBacks);

        // 为主线程创建一个 Runloop
        CFRunLoopRef mainLoop = __CFRunLoopCreate(pthread_main_thread_np());

        // 使用全局 Map 保存主线程 Runloop
        CFDictionarySetValue(dict, pthreadPointer(pthread_main_thread_np()), mainLoop);
    }

    // 通过全局 Map 获取 Runloop
    CFRunLoopRef loop = (CFRunLoopRef)CFDictionaryGetValue(__CFRunLoops, pthreadPointer(t));


    if (!loop) {
        // 如果未获取到 则创建一个
        CFRunLoopRef newLoop = __CFRunLoopCreate(t);
        // 重新获取一次 避免创建重复
        loop = (CFRunLoopRef)CFDictionaryGetValue(__CFRunLoops, pthreadPointer(t));
        if (!loop) {
            // 还是没有的话 将新创建的 Runloop 放入到全局 Map 中
            CFDictionarySetValue(__CFRunLoops, pthreadPointer(t), newLoop);
            loop = newLoop;
        }
    }
    return loop;
}

至于 __CFRunLoopCreate 创建函数则是创建了一个 CFRunLoopRef 类型的实例。并将其初始化。

static CFRunLoopRef __CFRunLoopCreate(pthread_t t) {
    CFRunLoopRef loop = NULL;
    CFRunLoopModeRef rlm;
    uint32_t size = sizeof(struct __CFRunLoop) - sizeof(CFRuntimeBase);
    loop = (CFRunLoopRef)_CFRuntimeCreateInstance(kCFAllocatorSystemDefault, CFRunLoopGetTypeID(), size, NULL);
    if (NULL == loop) {
    return NULL;
    }
    (void)__CFRunLoopPushPerRunData(loop);
    __CFRunLoopLockInit(&loop->_lock);
    loop->_wakeUpPort = __CFPortAllocate();
    if (CFPORT_NULL == loop->_wakeUpPort) HALT;
    __CFRunLoopSetIgnoreWakeUps(loop);
    loop->_commonModes = CFSetCreateMutable(kCFAllocatorSystemDefault, 0, &kCFTypeSetCallBacks);
    CFSetAddValue(loop->_commonModes, kCFRunLoopDefaultMode);
    loop->_commonModeItems = NULL;
    loop->_currentMode = NULL;
    loop->_modes = CFSetCreateMutable(kCFAllocatorSystemDefault, 0, &kCFTypeSetCallBacks);
    loop->_blocks_head = NULL;
    loop->_blocks_tail = NULL;
    loop->_counterpart = NULL;
    loop->_pthread = t;
#if DEPLOYMENT_TARGET_WINDOWS
    loop->_winthread = GetCurrentThreadId();
#else
    loop->_winthread = 0;
#endif
    rlm = __CFRunLoopFindMode(loop, kCFRunLoopDefaultMode, true);
    if (NULL != rlm) __CFRunLoopModeUnlock(rlm);
    return loop;
}

RunLoop 是如何运行的

要了解 RunLoop 是如何运行的，首先得先看一下他的结构。

RunLoop的结构

struct __CFRunLoop {
    CFRuntimeBase _base;
    pthread_mutex_t _lock;            /* locked for accessing mode list */
    __CFPort _wakeUpPort;            // used for CFRunLoopWakeUp 
    Boolean _unused;
    volatile _per_run_data *_perRunData;              // reset for runs of the run loop
    pthread_t _pthread;
    uint32_t _winthread;
    CFMutableSetRef _commonModes;
    CFMutableSetRef _commonModeItems;
    CFRunLoopModeRef _currentMode;
    CFMutableSetRef _modes;
    struct _block_item *_blocks_head;
    struct _block_item *_blocks_tail;
    CFAbsoluteTime _runTime;
    CFAbsoluteTime _sleepTime;
    CFTypeRef _counterpart;
};

接下来分析一波,其中主要关注的是。

类型	变量名	作用
pthread_mutex_t	_lock	用来锁对于 model 的访问的
__CFPort	_wakeUpPort	唤醒当前 Runloop 的 port
pthread_t	_pthread	记录当前线程
CFMutableSetRef	_commonModes	保存定义为 common 的 mode 的集合
CFMutableSetRef	_commonModeItems	保存定义为 common 的 mode 的 source、timer 和 observe
CFRunLoopModeRef	_currentMode	当前运行在哪个 mode 下
CFMutableSetRef	_modes	所有的 mode 的集合

CFRunLoopModeRef的结构

typedef struct __CFRunLoopMode *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 */
};

他们的作用是

类型	变量名	作用
pthread_mutex_t	_lock	用来锁对于 model 的访问的
CFStringRef	_name	当前 mode 的名称
CFMutableSetRef	_sources0	sources0的集合
CFMutableSetRef	_sources1	sources1的集合
CFMutableArrayRef	_observers	监听者的集合
CFMutableArrayRef	_timers	定时器的集合
CFMutableDictionaryRef	_portToV1SourceMap	一个字典用于记录 MachPort 和source1的映射关系
__CFPortSet	_portSet	端口的集合
dispatch_source_t	_timerSource	DISPATCH的定时器
dispatch_queue_t	_queue	_timerSource的队列
mach_port_t	_timerPort	MK 定时器端口

source0 和 sources1 的区别

其中需要注意的是 sources0 看起来和 sources1 差不多，其实还是又区别的。从源码的角度上来看
source0 最终执行到__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
而sources1最终执行到__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__

static void __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__() __attribute__((noinline));
static void __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__(void (*perform)(void *), void *info) {
    if (perform) {
        perform(info);
    }
    asm __volatile__(""); // thwart tail-call optimization
}

static void __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__() __attribute__((noinline));
static void __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__(
#if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED || DEPLOYMENT_TARGET_EMBEDDED_MINI
        void *(*perform)(void *msg, CFIndex size, CFAllocatorRef allocator, void *info),
        mach_msg_header_t *msg, CFIndex size, mach_msg_header_t **reply,
#else
        void (*perform)(void *),
#endif
        void *info) {
    if (perform) {
#if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED || DEPLOYMENT_TARGET_EMBEDDED_MINI
        *reply = perform(msg, size, kCFAllocatorSystemDefault, info);
#else
        perform(info);
#endif
    }
    asm __volatile__(""); // thwart tail-call optimization
}

对比源码发现source在 MACOSX 平台和EMBEDDED(嵌入式平台)做了一些涉及内核mach_msg的操作，想了解具体内容的同学可以自行搜索，我也还没太弄清楚。

Runloop 的入口

苹果为NSRunLoop提供了三个运行函数，分别是

- (void)run; 
- (void)runUntilDate:(NSDate *)limitDate;
- (BOOL)runMode:(NSRunLoopMode)mode beforeDate:(NSDate *)limitDate;

但是其实只有两个函数起作用run函数的内部其实是调用了runUntilDate,想了解NSRunloop的源码的朋友可以通过genstep查看。而其最终对应的Runloop为

void CFRunLoopRun(void) {    /* DOES CALLOUT */
    int32_t result;
    do {
        result = CFRunLoopRunSpecific(CFRunLoopGetCurrent(), kCFRunLoopDefaultMode, 1.0e10, false);
        CHECK_FOR_FORK();
    } while (kCFRunLoopRunStopped != result && kCFRunLoopRunFinished != result);
}

SInt32 CFRunLoopRunInMode(CFStringRef modeName, CFTimeInterval seconds, Boolean returnAfterSourceHandled) {     /* DOES CALLOUT */
    CHECK_FOR_FORK();
    return CFRunLoopRunSpecific(CFRunLoopGetCurrent(), modeName, seconds, returnAfterSourceHandled);
}

会发现他们最终都会调用CFRunLoopRunSpecific函数

SInt32 CFRunLoopRunSpecific(CFRunLoopRef rl, CFStringRef modeName, CFTimeInterval seconds, Boolean returnAfterSourceHandled) {     /* DOES CALLOUT */
    CHECK_FOR_FORK();

    if (__CFRunLoopIsDeallocating(rl)) return kCFRunLoopRunFinished;

    __CFRunLoopLock(rl);
    CFRunLoopModeRef currentMode = __CFRunLoopFindMode(rl, modeName, false);
    if (NULL == currentMode || __CFRunLoopModeIsEmpty(rl, currentMode, rl->_currentMode)) {
        Boolean did = false;
        if (currentMode) __CFRunLoopModeUnlock(currentMode);
        __CFRunLoopUnlock(rl);
        return did ? kCFRunLoopRunHandledSource : kCFRunLoopRunFinished;
    }
    volatile _per_run_data *previousPerRun = __CFRunLoopPushPerRunData(rl);
    CFRunLoopModeRef previousMode = rl->_currentMode;
    rl->_currentMode = currentMode;
    int32_t result = kCFRunLoopRunFinished;

    if (currentMode->_observerMask & kCFRunLoopEntry ) __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopEntry);
    result = __CFRunLoopRun(rl, currentMode, seconds, returnAfterSourceHandled, previousMode);
    if (currentMode->_observerMask & kCFRunLoopExit ) __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit);

        __CFRunLoopModeUnlock(currentMode);
        __CFRunLoopPopPerRunData(rl, previousPerRun);
    rl->_currentMode = previousMode;
    __CFRunLoopUnlock(rl);
    return result;
}

这里主要的逻辑是各种判空处理和设置currentMode以及通知Observers涉及到的Runloop的两种状态kCFRunLoopEntry kCFRunLoopExit。真正涉及到source timer等事件处理主要是在__CFRunLoopRun 函数中，代码太长就不贴了。最终运行逻辑如下图黑圈部分。

定时器

iOS定时器大致三种

NSTimer

这里有 gnustep 给出的源码地址，想要了解的朋友可以去查看。其本质也就是CFRunLoopTimerRef，需要将其添加进Runloop中才可以运行。优点是面向对象使用，用起来比较方便，缺点是需要将其添加进入标记为common的Runloop中，因为timer默认是添加的 default 的 mode 中，在用户拖拽滚动屏幕时会造成回调事件无法响应。另外由于是依赖Runloop所以如果单次Runloop处理的事情较多，耗时比较久，会造成响应的时间不准确。

CADisplayLink

CADisplayLink是一个和屏幕刷新率一致的定时器。运行时仍然依赖Runloop，但其原理和NSTimer不同，后续会有单独博客来写。每当屏幕显示内容刷新结束的时候，Runloop就会向CADisplayLink指定的target发送一次指定的selector消息， CADisplayLink类对应的 selector 就会被调用一次。如果在两次屏幕刷新之间执行了一个长任务，那其中就会有一帧被跳过，那么回调事件也将少一次，经常被用作监控FPS。

GCD

精确度高，不受Runloop影响

// 创建GCD定时器
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);

dispatch_source_set_timer(_timer, dispatch_walltime(NULL, 0), 1.0 * NSEC_PER_SEC, 0); //每秒执行

// 事件回调
dispatch_source_set_event_handler(_timer, ^{

    dispatch_async(dispatch_get_main_queue(), ^{
        // 在主线程中实现需要的功能

    }
}

});

// 开启定时器
dispatch_resume(_timer);

// 挂起定时器（dispatch_suspend 之后的 Timer，是不能被释放的！会引起崩溃）
dispatch_suspend(_timer);

// 关闭定时器
dispatch_source_cancel(_timer);

Autorelease

在APP启动时打印[NSRunloop mainRunLoop]

<CFRunLoop 0x60000186c000 [0x7fff80617cb0]>{wakeup port = 0x1a03, stopped = false, ignoreWakeUps = false, 
current mode = kCFRunLoopDefaultMode,
common modes = <CFBasicHash 0x600002a52160 [0x7fff80617cb0]>{type = mutable set, count = 2,
entries =>
    0 : <CFString 0x7fff867f6c40 [0x7fff80617cb0]>{contents = "UITrackingRunLoopMode"}
    2 : <CFString 0x7fff8062b0a0 [0x7fff80617cb0]>{contents = "kCFRunLoopDefaultMode"}
}
,
common mode items = <CFBasicHash 0x600002a52c70 [0x7fff80617cb0]>{type = mutable set, count = 11,
entries =>
    0 : <CFRunLoopSource 0x60000116c180 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 0, info = 0x0, callout = PurpleEventSignalCallback (0x7fff384c19f5)}}
    1 : <CFRunLoopObserver 0x60000156c5a0 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2000000, callout = _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv (0x7fff2b0c046e), context = <CFRunLoopObserver context 0x0>}
    2 : <CFRunLoopObserver 0x60000156c460 [0x7fff80617cb0]>{valid = Yes, activities = 0x1, repeats = Yes, order = -2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x7fff4808bf54), context = <CFArray 0x600002a04a80 [0x7fff80617cb0]>{type = mutable-small, count = 1, values = (
    0 : <0x7f8956803038>
)}}
    3 : <CFRunLoopSource 0x60000116c600 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -2, context = <CFRunLoopSource context>{version = 0, info = 0x600002a31ef0, callout = __handleHIDEventFetcherDrain (0x7fff48126da3)}}
    6 : <CFRunLoopSource 0x6000011683c0 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = 0, context = <CFRunLoopSource context>{version = 0, info = 0x60000007c0c0, callout = FBSSerialQueueRunLoopSourceHandler (0x7fff3662186a)}}
    7 : <CFRunLoopObserver 0x60000156c320 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 1999000, callout = _beforeCACommitHandler (0x7fff480bc2eb), context = <CFRunLoopObserver context 0x7f8954c01140>}
    8 : <CFRunLoopSource 0x600001160300 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 1, info = 0x3003, callout = PurpleEventCallback (0x7fff384c1a01)}}
    9 : <CFRunLoopObserver 0x60000156c500 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x7fff4808bf54), context = <CFArray 0x600002a04a80 [0x7fff80617cb0]>{type = mutable-small, count = 1, values = (
    0 : <0x7f8956803038>
)}}
    10 : <CFRunLoopObserver 0x6000015646e0 [0x7fff80617cb0]>{valid = Yes, activities = 0x20, repeats = Yes, order = 0, callout = _UIGestureRecognizerUpdateObserver (0x7fff47c2f06a), context = <CFRunLoopObserver context 0x600000f656c0>}
    11 : <CFRunLoopObserver 0x60000156c3c0 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2001000, callout = _afterCACommitHandler (0x7fff480bc354), context = <CFRunLoopObserver context 0x7f8954c01140>}
    12 : <CFRunLoopSource 0x60000116c3c0 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 0, info = 0x600001160480, callout = __handleEventQueue (0x7fff48126d97)}}
}
,
modes = <CFBasicHash 0x600002a51ec0 [0x7fff80617cb0]>{type = mutable set, count = 3,
entries =>
    0 : <CFRunLoopMode 0x600001f68270 [0x7fff80617cb0]>{name = UITrackingRunLoopMode, port set = 0x1f03, queue = 0x600000a6c980, source = 0x600000a6ca80 (not fired), timer port = 0x2a03, 
    sources0 = <CFBasicHash 0x600002a52cd0 [0x7fff80617cb0]>{type = mutable set, count = 4,
entries =>
    0 : <CFRunLoopSource 0x60000116c180 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 0, info = 0x0, callout = PurpleEventSignalCallback (0x7fff384c19f5)}}
    3 : <CFRunLoopSource 0x60000116c3c0 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 0, info = 0x600001160480, callout = __handleEventQueue (0x7fff48126d97)}}
    4 : <CFRunLoopSource 0x6000011683c0 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = 0, context = <CFRunLoopSource context>{version = 0, info = 0x60000007c0c0, callout = FBSSerialQueueRunLoopSourceHandler (0x7fff3662186a)}}
    5 : <CFRunLoopSource 0x60000116c600 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -2, context = <CFRunLoopSource context>{version = 0, info = 0x600002a31ef0, callout = __handleHIDEventFetcherDrain (0x7fff48126da3)}}
}
,
    sources1 = <CFBasicHash 0x600002a52d00 [0x7fff80617cb0]>{type = mutable set, count = 1,
entries =>
    0 : <CFRunLoopSource 0x600001160300 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 1, info = 0x3003, callout = PurpleEventCallback (0x7fff384c1a01)}}
}
,
    observers = (
    "<CFRunLoopObserver 0x60000156c460 [0x7fff80617cb0]>{valid = Yes, activities = 0x1, repeats = Yes, order = -2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x7fff4808bf54), context = <CFArray 0x600002a04a80 [0x7fff80617cb0]>{type = mutable-small, count = 1, values = (\n\t0 : <0x7f8956803038>\n)}}",
    "<CFRunLoopObserver 0x6000015646e0 [0x7fff80617cb0]>{valid = Yes, activities = 0x20, repeats = Yes, order = 0, callout = _UIGestureRecognizerUpdateObserver (0x7fff47c2f06a), context = <CFRunLoopObserver context 0x600000f656c0>}",
    "<CFRunLoopObserver 0x60000156c320 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 1999000, callout = _beforeCACommitHandler (0x7fff480bc2eb), context = <CFRunLoopObserver context 0x7f8954c01140>}",
    "<CFRunLoopObserver 0x60000156c5a0 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2000000, callout = _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv (0x7fff2b0c046e), context = <CFRunLoopObserver context 0x0>}",
    "<CFRunLoopObserver 0x60000156c3c0 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2001000, callout = _afterCACommitHandler (0x7fff480bc354), context = <CFRunLoopObserver context 0x7f8954c01140>}",
    "<CFRunLoopObserver 0x60000156c500 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x7fff4808bf54), context = <CFArray 0x600002a04a80 [0x7fff80617cb0]>{type = mutable-small, count = 1, values = (\n\t0 : <0x7f8956803038>\n)}}"
),
    timers = (null),
    currently 604176379 (711094024663053) / soft deadline in: 1.8446033e+10 sec (@ -1) / hard deadline in: 1.8446033e+10 sec (@ -1)
},

    1 : <CFRunLoopMode 0x600001f68340 [0x7fff80617cb0]>{name = GSEventReceiveRunLoopMode, port set = 0x2c03, queue = 0x600000a6cb00, source = 0x600000a6cc00 (not fired), timer port = 0x2f03, 
    sources0 = <CFBasicHash 0x600002a52d90 [0x7fff80617cb0]>{type = mutable set, count = 1,
entries =>
    0 : <CFRunLoopSource 0x60000116c180 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 0, info = 0x0, callout = PurpleEventSignalCallback (0x7fff384c19f5)}}
}
,
    sources1 = <CFBasicHash 0x600002a52dc0 [0x7fff80617cb0]>{type = mutable set, count = 1,
entries =>
    0 : <CFRunLoopSource 0x6000011603c0 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 1, info = 0x3003, callout = PurpleEventCallback (0x7fff384c1a01)}}
}
,
    observers = (null),
    timers = (null),
    currently 604176379 (711094025794486) / soft deadline in: 1.8446033e+10 sec (@ -1) / hard deadline in: 1.8446033e+10 sec (@ -1)
},

    2 : <CFRunLoopMode 0x600001f681a0 [0x7fff80617cb0]>{name = kCFRunLoopDefaultMode, port set = 0x2403, queue = 0x600000a6c700, source = 0x600000a6c800 (not fired), timer port = 0x1b03, 
    sources0 = <CFBasicHash 0x600002a52d30 [0x7fff80617cb0]>{type = mutable set, count = 4,
entries =>
    0 : <CFRunLoopSource 0x60000116c180 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 0, info = 0x0, callout = PurpleEventSignalCallback (0x7fff384c19f5)}}
    3 : <CFRunLoopSource 0x60000116c3c0 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 0, info = 0x600001160480, callout = __handleEventQueue (0x7fff48126d97)}}
    4 : <CFRunLoopSource 0x6000011683c0 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = 0, context = <CFRunLoopSource context>{version = 0, info = 0x60000007c0c0, callout = FBSSerialQueueRunLoopSourceHandler (0x7fff3662186a)}}
    5 : <CFRunLoopSource 0x60000116c600 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -2, context = <CFRunLoopSource context>{version = 0, info = 0x600002a31ef0, callout = __handleHIDEventFetcherDrain (0x7fff48126da3)}}
}
,
    sources1 = <CFBasicHash 0x600002a52d60 [0x7fff80617cb0]>{type = mutable set, count = 1,
entries =>
    0 : <CFRunLoopSource 0x600001160300 [0x7fff80617cb0]>{signalled = No, valid = Yes, order = -1, context = <CFRunLoopSource context>{version = 1, info = 0x3003, callout = PurpleEventCallback (0x7fff384c1a01)}}
}
,
    observers = (
    "<CFRunLoopObserver 0x60000156c460 [0x7fff80617cb0]>{valid = Yes, activities = 0x1, repeats = Yes, order = -2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x7fff4808bf54), context = <CFArray 0x600002a04a80 [0x7fff80617cb0]>{type = mutable-small, count = 1, values = (\n\t0 : <0x7f8956803038>\n)}}",
    "<CFRunLoopObserver 0x6000015646e0 [0x7fff80617cb0]>{valid = Yes, activities = 0x20, repeats = Yes, order = 0, callout = _UIGestureRecognizerUpdateObserver (0x7fff47c2f06a), context = <CFRunLoopObserver context 0x600000f656c0>}",
    "<CFRunLoopObserver 0x60000156c320 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 1999000, callout = _beforeCACommitHandler (0x7fff480bc2eb), context = <CFRunLoopObserver context 0x7f8954c01140>}",
    "<CFRunLoopObserver 0x60000156c5a0 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2000000, callout = _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv (0x7fff2b0c046e), context = <CFRunLoopObserver context 0x0>}",
    "<CFRunLoopObserver 0x60000156c3c0 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2001000, callout = _afterCACommitHandler (0x7fff480bc354), context = <CFRunLoopObserver context 0x7f8954c01140>}",
    "<CFRunLoopObserver 0x60000156c500 [0x7fff80617cb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x7fff4808bf54), context = <CFArray 0x600002a04a80 [0x7fff80617cb0]>{type = mutable-small, count = 1, values = (\n\t0 : <0x7f8956803038>\n)}}"
),
    timers = <CFArray 0x60000006d920 [0x7fff80617cb0]>{type = mutable-small, count = 1, values = (
    0 : <CFRunLoopTimer 0x60000116c240 [0x7fff80617cb0]>{valid = Yes, firing = No, interval = 0, tolerance = 0, next fire date = 604176123 (-256.022397 @ 710837994489938), callout = (Delayed Perform) UIApplication _accessibilitySetUpQuickSpeak (0x7fff2576c7c2 / 0x7fff475e21aa) (/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/UIKitCore.framework/UIKitCore), context = <CFRunLoopTimer context 0x600003109540>}
)},
    currently 604176379 (711094025842302) / soft deadline in: 1.84467438e+10 sec (@ 710837994489938) / hard deadline in: 1.84467438e+10 sec (@ 710837994489938)
},

}
}

可以看到Runloop在每个RunloopMode中都注册了两个observers,

activities = 0xa0, order = 2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler 
activities = 0x1, order = -2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler

其中Runloop的状态变化的通知时机有以下这些。

/* Run Loop Observer Activities */
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
};

能看出来这个一个位枚举
activities = 0x1代表着kCFRunLoopEntry
activities = 0xa0代表着(kCFRunLoopBeforeWaiting | kCFRunLoopExit)

通过符号断点_wrapRunLoopWithAutoreleasePoolHandler能够看到具体的汇编实现

其中通过判断代码cmpq $0x80 cmpq $0x20 cmpq $0x1 实现如何调用NSPushAutoreleasePool和NSPopAutoreleasePool。

• 当前activities = kCFRunLoopEntry 直接走向NSPushAutoreleasePool向当前的AutoreleasePoolPage增加一个哨兵对象标志创建自动释放池。

• 当前activities = kCFRunLoopBeforeWaiting 会先运行NSPopAutoreleasePool将加入的对象逐个清理知道遇到哨兵对象。然后则调用NSPushAutoreleasePool。重新添加一个哨兵对象。

• 当前activities = kCFRunLoopEntry 直接走向NSPopAutoreleasePool清理当前的AutoreleasePool。

通过符号断点逐步查看，发现NSPushAutoreleasePool和NSPopAutoreleasePool最终会调用AutoreleasePoolPage::push()和AutoreleasePoolPage::pop(ctxt)这里可以看到具体的源码了。有兴趣的可以自行查看原理。