iOS的CoreFoundation框架是開源的
NSRunloop只是對CFRunLoop的封裝奋刽，CFRunLoop在CoreFoundation中政供。
示例demo

CFRunLoop

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;
    CFTypeRef _counterpart;
};

CFRunLoopMode

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 */
};

CFRunLoopSource

struct __CFRunLoopSource {
    CFRuntimeBase _base;
    uint32_t _bits;
    pthread_mutex_t _lock;
    CFIndex _order;            /* immutable */
    CFMutableBagRef _runLoops;
    union {
        CFRunLoopSourceContext version0;    /* immutable, except invalidation */
        CFRunLoopSourceContext1 version1;    /* immutable, except invalidation */
    } _context;
};

CFRunLoopObserver

struct __CFRunLoopObserver {
    CFRuntimeBase _base;
    pthread_mutex_t _lock;
    CFRunLoopRef _runLoop;
    CFIndex _rlCount;
    CFOptionFlags _activities;        /* immutable */
    CFIndex _order;            /* immutable */
    CFRunLoopObserverCallBack _callout;    /* immutable */
    CFRunLoopObserverContext _context;    /* immutable, except invalidation */
};

CFRunLoopTimer

struct __CFRunLoopTimer {
    CFRuntimeBase _base;
    uint16_t _bits;
    pthread_mutex_t _lock;
    CFRunLoopRef _runLoop;
    CFMutableSetRef _rlModes;
    CFAbsoluteTime _nextFireDate;
    CFTimeInterval _interval;        /* immutable */
    CFTimeInterval _tolerance;          /* mutable */
    uint64_t _fireTSR;            /* TSR units */
    CFIndex _order;            /* immutable */
    CFRunLoopTimerCallBack _callout;    /* immutable */
    CFRunLoopTimerContext _context;    /* immutable, except invalidation */
};

image1.png

RunLoop內(nèi)部執(zhí)行過程

SInt32 CFRunLoopRunSpecific(CFRunLoopRef rl, CFStringRef modeName, CFTimeInterval seconds, Boolean returnAfterSourceHandled) {     /* DOES CALLOUT */
    CHECK_FOR_FORK();
    if (__CFRunLoopIsDeallocating(rl)) return kCFRunLoopRunFinished;
    __CFRunLoopLock(rl);
    
    /// 首先根據(jù)modeName找到對應mode
    CFRunLoopModeRef currentMode = __CFRunLoopFindMode(rl, modeName, false);
    
    /// 通知 Observers: RunLoop 即將進入 loop愧旦。
    __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopEntry);
    
    /// 內(nèi)部函數(shù)缸匪，進入loop
    result = __CFRunLoopRun(rl, currentMode, seconds, returnAfterSourceHandled, previousMode);
    
    /// 通知 Observers: RunLoop 即將退出斋泄。
    __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit);
    
    return result;
}

/// 核心函數(shù)
static int32_t __CFRunLoopRun(CFRunLoopRef rl, CFRunLoopModeRef rlm, CFTimeInterval seconds, Boolean stopAfterHandle, CFRunLoopModeRef previousMode) {
    
    int32_t retVal = 0;
    
    do {  // itmes do
        
        /// 通知 Observers: 即將處理timer事件
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeTimers);
        
        /// 通知 Observers: 即將處理Source事件
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeSources)
        
        /// 處理Blocks
        __CFRunLoopDoBlocks(rl, rlm);
        
        /// 處理sources0
        Boolean sourceHandledThisLoop = __CFRunLoopDoSources0(rl, rlm, stopAfterHandle);
        
        /// 處理sources0返回為YES
        if (sourceHandledThisLoop) {
            /// 處理Blocks
            __CFRunLoopDoBlocks(rl, rlm);
        }
        
        
        /// 判斷有無端口消息(Source1)
        if (__CFRunLoopServiceMachPort(dispatchPort, &msg, sizeof(msg_buffer), &livePort, 0, &voucherState, NULL)) {
            /// 處理消息
            goto handle_msg;
        }
        
        /// 通知 Observers: 即將進入休眠
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeWaiting);
        __CFRunLoopSetSleeping(rl);
        
        /// 等待被喚醒
        __CFRunLoopServiceMachPort(waitSet, &msg, sizeof(msg_buffer), &livePort, poll ? 0 : TIMEOUT_INFINITY, &voucherState, &voucherCopy);
        
        
        // user callouts now OK again
        __CFRunLoopUnsetSleeping(rl);
        
        /// 通知 Observers: 被喚醒握侧，結(jié)束休眠
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopAfterWaiting);
        
    handle_msg:
        if (被Timer喚醒) {
            /// 處理Timers
            __CFRunLoopDoTimers(rl, rlm, mach_absolute_time())亲雪；
        } else if (被GCD喚醒) {
            /// 處理gcd
            __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__(msg);
        } else if (被Source1喚醒) {
            /// 被Source1喚醒里初，處理Source1
            __CFRunLoopDoSource1(rl, rlm, rls, msg, msg->msgh_size, &reply)
        }
        
        /// 處理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__

image2.png

分析示例

#import "ViewController.h"
//#import "LGThread.h"
#import <objc/message.h>

@interface ViewController ()<NSPortDelegate>
@property (nonatomic, strong) NSPort* subThreadPort;
@property (nonatomic, strong) NSPort* mainThreadPort;
//@property (nonatomic, assign) BOOL isStopping;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

//    [self testThredRunLoop];

//    [self cfTimerDemo];
    
//    [self cfObseverDemo];
    
//    [self source0Demo];
    
    [self setupPort];
}

//- (void)testThredRunLoop  {
//    // runloop 和 線程
//    // 主運行循環(huán)
//     CFRunLoopRef mainRunloop = CFRunLoopGetMain();
//     // 當前運行循環(huán)
//     CFRunLoopRef currentRunloop = CFRunLoopGetCurrent();
//
//    // 子線程runloop 默認不啟動
//
//    self.isStopping = NO;
//    LGThread *thread = [[LGThread alloc] initWithBlock:^{
//
//        // thread.name = nil 因為這個變量只是捕捉
//        // LGThread *thread = nil
//        // thread = 初始化 捕捉一個nil進來
//        NSLog(@"%@---%@",[NSThread currentThread],[[NSThread currentThread] name]);
//        [NSTimer scheduledTimerWithTimeInterval:1 repeats:YES block:^(NSTimer * _Nonnull timer) {
//            NSLog(@"hello word");            // 退出線程--結(jié)果runloop也停止了
//            if (self.isStopping) {
//                [NSThread exit];
//            }
//        }];
//         [[NSRunLoop currentRunLoop] run];
//    }];
//
//    thread.name = @"lgcode.com";
//    [thread start];
//}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    
//    self.isStopping = YES;
    
    NSMutableArray* components = [NSMutableArray array];
    NSData* data = [@"hello" dataUsingEncoding:NSUTF8StringEncoding];
    [components addObject:data];
    [self.subThreadPort sendBeforeDate:[NSDate date] components:components from:self.mainThreadPort reserved:0];
}

#pragma mark - mode演練
- (void)timerDemo{
    
    // CFRunLoopMode 研究
    CFRunLoopRef lp     = CFRunLoopGetCurrent();
    CFRunLoopMode mode  = CFRunLoopCopyCurrentMode(lp);
    NSLog(@"mode == %@",mode);
    CFArrayRef modeArray= CFRunLoopCopyAllModes(lp);
    NSLog(@"modeArray == %@",modeArray);

    NSTimer *timer = [NSTimer timerWithTimeInterval:1 repeats:YES block:^(NSTimer * _Nonnull timer) {
        NSLog(@"fire in home -- %@",[[NSRunLoop currentRunLoop] currentMode]);
    }];
    [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
}

#pragma mark - timer
- (void)cfTimerDemo{
    CFRunLoopTimerContext context = {
        0,
        ((__bridge void *)self),
        NULL,
        NULL,
        NULL
    };
    CFRunLoopRef rlp = CFRunLoopGetCurrent();
    /**
     參數(shù)一:用于分配對象的內(nèi)存
     參數(shù)二:在什么是觸發(fā) (距離現(xiàn)在)
     參數(shù)三:每隔多少時間觸發(fā)一次
     參數(shù)四:未來參數(shù)
     參數(shù)五:CFRunLoopObserver的優(yōu)先級 當在Runloop同一運行階段中有多個CFRunLoopObserver 正常情況下使用0
     參數(shù)六:回調(diào),比如觸發(fā)事件,我就會來到這里
     參數(shù)七:上下文記錄信息
     */
    CFRunLoopTimerRef timerRef = CFRunLoopTimerCreate(kCFAllocatorDefault, 0, 1, 0, 0, lgRunLoopTimerCallBack, &context);
    CFRunLoopAddTimer(rlp, timerRef, kCFRunLoopDefaultMode);

}

void lgRunLoopTimerCallBack(CFRunLoopTimerRef timer, void *info){
    NSLog(@"%@---%@",timer,info);
}

#pragma mark - observe
- (void)cfObseverDemo{
    
    CFRunLoopObserverContext context = {
        0,
        ((__bridge void *)self),
        NULL,
        NULL,
        NULL
    };
    CFRunLoopRef rlp = CFRunLoopGetCurrent();
    /**
     參數(shù)一:用于分配對象的內(nèi)存
     參數(shù)二:你關注的事件
          kCFRunLoopEntry=(1<<0),
          kCFRunLoopBeforeTimers=(1<<1),
          kCFRunLoopBeforeSources=(1<<2),
          kCFRunLoopBeforeWaiting=(1<<5),
          kCFRunLoopAfterWaiting=(1<<6),
          kCFRunLoopExit=(1<<7),
          kCFRunLoopAllActivities=0x0FFFFFFFU
     參數(shù)三:CFRunLoopObserver是否循環(huán)調(diào)用
     參數(shù)四:CFRunLoopObserver的優(yōu)先級 當在Runloop同一運行階段中有多個CFRunLoopObserver 正常情況下使用0
     參數(shù)五:回調(diào),比如觸發(fā)事件,我就會來到這里
     參數(shù)六:上下文記錄信息
     */
    CFRunLoopObserverRef observerRef = CFRunLoopObserverCreate(kCFAllocatorDefault, kCFRunLoopAllActivities, YES, 0, lgRunLoopObserverCallBack, &context);
    CFRunLoopAddObserver(rlp, observerRef, kCFRunLoopDefaultMode);
}

void lgRunLoopObserverCallBack(CFRunLoopObserverRef observer, CFRunLoopActivity activity, void *info){
    NSLog(@"%lu-%@",activity,info);
}

#pragma mark - source0:演練

// 就是喜歡玩一下: 我們下面來自定義一個source
- (void)source0Demo{
    
    CFRunLoopSourceContext context = {
        0,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        schedule,
        cancel,
        perform,
    };
    /**
     
     參數(shù)一:傳遞NULL或kCFAllocatorDefault以使用當前默認分配器惨好。
     參數(shù)二:優(yōu)先級索引煌茴，指示處理運行循環(huán)源的順序。這里我傳0為了的就是自主回調(diào)
     參數(shù)三:為運行循環(huán)源保存上下文信息的結(jié)構
     */
    CFRunLoopSourceRef source0 = CFRunLoopSourceCreate(CFAllocatorGetDefault(), 0, &context);
    CFRunLoopRef rlp = CFRunLoopGetCurrent();
    // source --> runloop 指定了mode  那么此時我們source就進入待緒狀態(tài)
    CFRunLoopAddSource(rlp, source0, kCFRunLoopDefaultMode);
    // 一個執(zhí)行信號
    CFRunLoopSourceSignal(source0);
    // 喚醒 run loop 防止沉睡狀態(tài)
    CFRunLoopWakeUp(rlp);
    // 取消 移除
    CFRunLoopRemoveSource(rlp, source0, kCFRunLoopDefaultMode);
    CFRelease(rlp);
}

void schedule(void *info, CFRunLoopRef rl, CFRunLoopMode mode){
    NSLog(@"準備代發(fā)");
}

void perform(void *info){
    NSLog(@"執(zhí)行吧,騷年");
}

void cancel(void *info, CFRunLoopRef rl, CFRunLoopMode mode){
    NSLog(@"取消了,終止了!!!!");
}

#pragma mark - source1: port演示

- (void)setupPort{
    
    self.mainThreadPort = [NSPort port];
    self.mainThreadPort.delegate = self;
    // port - source1 -- runloop
    [[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 start];
    // 主線 -- 子線程
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"%@", [NSThread currentThread]); // 3

        NSString *str;
        dispatch_async(dispatch_get_main_queue(), ^{
            // 1
            NSLog(@"%@", [NSThread currentThread]);

        });
    });
}

// 線程之間通訊
// 主線程 -- data
// 子線程 -- data1
// 更加低層 -- 內(nèi)核
// mach

- (void)handlePortMessage:(id)message {
    NSLog(@"%@", [NSThread currentThread]); // 3 1

    unsigned int count = 0;
    Ivar *ivars = class_copyIvarList([message class], &count);
    for (int i = 0; i<count; i++) {
        
        NSString *name = [NSString stringWithUTF8String:ivar_getName(ivars[i])];
//        NSLog(@"%@",name);
    }
    
    sleep(1);
    if (![[NSThread currentThread] isMainThread]) {

        NSMutableArray* components = [NSMutableArray array];
        NSData* data = [@"woard" dataUsingEncoding:NSUTF8StringEncoding];
        [components addObject:data];

        [self.mainThreadPort sendBeforeDate:[NSDate date] components:components from:self.subThreadPort reserved:0];
    }
}
@end

參考文章：
iOS進階-Runloop源碼探究
iOS 透過CFRunloop源碼分析runloop底層原理及應用場景