RunLoop知識合集如下圖：

RunLoop.png

CFRunLoop簡化后的代碼分析

static int32_t __CFRunLoopRun(CFRunLoopRef rl, CFRunLoopModeRef rlm, CFTimeInterval seconds, Boolean stopAfterHandle, CFRunLoopModeRef previousMode) {
    
    Boolean didDispatchPortLastTime = true;
    int32_t retVal = 0;
    do {
        
        //通知Observers:即將處理Timers
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeTimers);
        //通知Observers:即將處理Sources
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeSources);
        //處理Blocks
        __CFRunLoopDoBlocks(rl, rlm);
        
        //處理Sources0
        __CFRunLoopDoSources0(rl, rlm, stopAfterHandle);
        if (sourceHandledThisLoop) {
            //有可能再次處理Blocks
            __CFRunLoopDoBlocks(rl, rlm);
        }
        
        //判斷是否有sources1,就跳轉到handle_msg標記處
        if (__CFRunLoopServiceMachPort(dispatchPort, &msg, sizeof(msg_buffer), &livePort, 0, &voucherState, NULL)) {
            goto handle_msg;
        }

        //通知Observers：即將進入休眠
        __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeWaiting);
        
        //進入休眠，等待其他消息喚醒
        __CFRunLoopSetSleeping(rl);
        __CFPortSetInsert(dispatchPort, waitSet);
        do {
           
            __CFRunLoopServiceMachPort(waitSet, &msg, sizeof(msg_buffer), &livePort, poll ? 0 : TIMEOUT_INFINITY, &voucherState, &voucherCopy);
        } while (1);
        
        if (kCFUseCollectableAllocator) {
            // objc_clear_stack(0);
            // <rdar://problem/16393959>
            memset(msg_buffer, 0, sizeof(msg_buffer));
        }
      
        //醒來
        __CFPortSetRemove(dispatchPort, waitSet);
        __CFRunLoopUnsetSleeping(rl);
        
        //通知Observers:已經(jīng)喚醒
       __CFRunLoopDoObservers(rl, rlm, kCFRunLoopAfterWaiting);
        
    handle_msg: //看看是誰喚醒了RunLoop，進行相應的處理

        if (被timer喚醒的) {
         //處理Timer
          CFRunLoopDoTimers(rl, rlm, mach_absolute_time()))
        }
        else if (被GCD喚醒的) {
            __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__(msg);
        } else {
            //被source1喚醒的
            sourceHandledThisLoop = __CFRunLoopDoSource1(rl, rlm, rls, msg, msg->msgh_size, &reply);
        }

        //執(zhí)行Blocks
        __CFRunLoopDoBlocks(rl, rlm);
        
        //根據(jù)之前的執(zhí)行結果，來決定怎么做
        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;
        }
        
        voucher_mach_msg_revert(voucherState);
        os_release(voucherCopy);
        
    } while (0 == retVal);
    
    return retVal;
}



SInt32 CFRunLoopRunSpecific(CFRunLoopRef rl, CFStringRef modeName, CFTimeInterval seconds, Boolean returnAfterSourceHandled) {     /* DOES CALLOUT */
    
    //通知Observer:進入Loop
    __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopEntry);
    
    //核心的Loop邏輯
    __CFRunLoopRun(rl, currentMode, seconds, returnAfterSourceHandled, previousMode);
    
    //通知Observer:退出Loop
    __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit);
    
    return result;
}



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