What does iOS RunLoop do?

RunLoop flow chart

The upload – images. Jianshu. IO/upload_imag…

What does RunLoop do from the entry function?

CFRunLoopRun: CFRunLoopRun: do… 2.CFRunLoopRunSpecific passes the current Loop, default Model, second value 1.0e10, BOOL returnAfterSourceHandled.

CFRunLoopRunSpecific (CFRunLoopGetCurrent (), kCFRunLoopDefaultMode, 1.0 e10,false);
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3. Based on the modeName passed in, __CFRunLoopFindMode is used to get the current CFRunLoopModeRef currentMode. 4. If no event is found or registered in mode, the loop is stopped

    if (NULL == currentMode || __CFRunLoopModeIsEmpty(rl, currentMode, rl->_currentMode)) {
        Boolean did = false;
        if (currentMode) __CFRunLoopModeUnlock(currentMode);
        __CFRunLoopUnlock(rl);
        return did ? kCFRunLoopRunHandledSource : kCFRunLoopRunFinished;
    }
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Take the last runmode, the currentrunloopthemodeReplace it with what you found in step 3mode

    CFRunLoopModeRef previousMode = rl->_currentMode;
    rl->_currentMode = currentMode;
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6. Initialize result as kCFRunLoopRunFinished, notify Observers: RunLoop is about to enter loop, and __CFRunLoopRun is set to result. RunLoop is about to exit.

    int32_t result = kCFRunLoopRunFinished;
    if(currentMode->_observerMask & kCFRunLoopEntry ){ /// 1. Notifying Observers: RunLoop is about to enter loop. __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopEntry); } result = __CFRunLoopRun(rl, currentMode, seconds,returnAfterSourceHandled, previousMode);
    if(currentMode->_observerMask & kCFRunLoopExit ){ /// 10. Notify Observers: RunLoop is about to exit. __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit); }Copy the code

7. When the RunLoop exits, it performs a series of operations. The Unlock is currently in the mode obtained in step 3, sets the _currentMode of the current RunLoop to the previousMode that was saved, and returns result.

    __CFRunLoopModeUnlock(currentMode);
    __CFRunLoopPopPerRunData(rl, previousPerRun);
    rl->_currentMode = previousMode;
    __CFRunLoopUnlock(rl);
    return result;
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Core method`__CFRunLoopRun`What did you do?

1. Inform the Observer that RunLoop is about to enter

if (currentMode->_observerMask & kCFRunLoopEntry ){
    __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopEntry);
}
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__CFRunLoopRun executes what is in the dotted box above, described in the order shown. 2. Notify the Observer that the Timer will be processed

if (rlm->_observerMask & kCFRunLoopBeforeTimers) {
    __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeTimers);
}
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3. Inform the Observer that source0 will be processed

if (rlm->_observerMask & kCFRunLoopBeforeSources) {
    __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeSources);
}
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4. Handle source0

    Boolean sourceHandledThisLoop = __CFRunLoopDoSources0(rl, rlm, stopAfterHandle);
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5. If there is source1, go to step 9. Source1 contains a mach_port and a callback (function pointer),

    msg = (mach_msg_header_t *)msg_buffer;
    if(__CFRunLoopServiceMachPort(dispatchPort, &msg, sizeof(msg_buffer), &livePort, 0)) {// If a message is received, Goto step 9 and start processing MSG goto handle_msg; }Copy the code

6. Notify the Observer that runloop is going to sleep. Poll is false if there is no sources0 event processing and no timeout; Poll is true if sources0 event processing or timeout occurs. If poll is false and RLM ->_observerMask is kCFRunLoopBeforeWaiting, __CFRunLoopDoObservers is executed.

if(! poll && (rlm->_observerMask & kCFRunLoopBeforeWaiting)) __CFRunLoopDoObservers(rl, rlm, kCFRunLoopBeforeWaiting);Copy the code

7. Set runloop to sleep __CFRunLoopSetSleeping(rl); After executing an inner loop do… While, the thread enters the loop and goes to sleep until it receives a new message and then breaks out of the loop (being woken up) and continues executing the Run loop.

Here’s a twist: Why is the runloop set to sleep, but the thread?

Runloops correspond to threads one by one. A runloop corresponds to a core thread, which is core because runloops can be nested, but there can only be one core, and their relationship is stored in a global dictionary. Runloop is used to manage threads. When a thread’s Runloop is enabled, the thread will go to sleep after executing a task. When a task is available, the thread will be awakened to perform the task.

The paragraph above is taken from the bigwig

An internal loop is executed if USE_DISPATCH_SOURCE_FOR_TIMERS is waiting for awakening

do{// Read messages from the buffer MSG = (mach_MSG_header_t *)msg_buffer; / / 7. Call __CFRunLoopServiceMachPort, listeningwaitIf there is no port message, mach_MSg_trap will be entered and RunLoop will sleep until a port message is received or the __CFRunLoopServiceMachPort(waitSet, &msg, sizeof(msg_buffer), &livePort, poll ? 0 : TIMEOUT_INFINITY); MSG ->msgh_local_port, then livePort! =modeQueuePort, so it will walkelse
            if(modeQueuePort ! = MACH_PORT_NULL && livePort == modeQueuePort) { // Drain the internal queue. If one of the callout blocks sets the timerFired flag,breakOut and service the timer. // Exhaust the internal queue if there is a callback block set to timerFired, breaks out of the loop and serves the timer.while (_dispatch_runloop_root_queue_perform_4CF(rlm->_queue));
                if (rlm->_timerFired) {
                    // Leave livePort as the queue port, and service timers below
                    rlm->_timerFired = false;
                    break; // Exit the loop to perform a wake up operation}else{// If MSG is not empty and does not match msg_buffer, release the MSG as if nothing happenedif (msg && msg != (mach_msg_header_t *)msg_buffer) free(msg);
                }
            } else{// Go ahead and leave the inner loopbreak; // Exit the loop to perform a wake up operation}}while (1);
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One of the things that really bothers me here is what all these various ports are and how livePorts are equal to Modequeueports.

 if(modeQueuePort ! = MACH_PORT_NULL && livePort == modeQueuePort)Copy the code

How does this judgment work? I searched globally for modeQueuePort and found only one place with an assignment that required USE_DISPATCH_SOURCE_FOR_TIMERS.

modeQueuePort = _dispatch_runloop_root_queue_get_port_4CF(rlm->_queue);
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When the kernel successfully receives the message, the livePort is assigned the value MSG -> MSgh_LOCAL_port

if(MACH_MSG_SUCCESS == ret) {// Message received successfully *livePort = MSG? msg->msgh_local_port : MACH_PORT_NULL;return true;
}
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So, as long as the message is successfully received, the livePort is not equal to the modeQueuePort, and the loop is broken.

Further down the line, however, you see a string of code with the same rules, but with a method that wakes up RunLoop.

#if USE_DISPATCH_SOURCE_FOR_TIMERS
       if(modeQueuePort ! = MACH_PORT_NULL && livePort == modeQueuePort) { CFRUNLOOP_WAKEUP_FOR_TIMER();if (!__CFRunLoopDoTimers(rl, rlm, mach_absolute_time())) {
                // Re-arm the next timer, because we apparently fired early
                __CFArmNextTimerInMode(rlm, rl);
            }
        }
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Oh, my god, what shit? It’s hard to read it out, but it’s a conflict here, and I doubt life. Scared me into looking for information. Finally, I found an explanation of this passage in the big guy’s blog.

Instead of waking up after runLoop sleep, it jumps in at step 5 of runLoop10 to handle timer events

At last the inner circle was more or less clear

8. Inform the Observer that the thread has just been awakened. The hibernation is over.

if(! poll && (rlm->_observerMask & kCFRunLoopAfterWaiting)) { __CFRunLoopDoObservers(rl, rlm, kCFRunLoopAfterWaiting); }Copy the code

9: Process the messages received on wake up, then go back to step 2.

handle_msg:;
        __CFRunLoopSetIgnoreWakeUps(rl);
         if (MACH_PORT_NULL == livePort) {
            CFRUNLOOP_WAKEUP_FOR_NOTHING();
            // handle nothing
        } else if (livePort == rl->_wakeUpPort) {
            CFRUNLOOP_WAKEUP_FOR_WAKEUP();
            // do nothing on Mac OS
        }
#if USE_DISPATCH_SOURCE_FOR_TIMERS
        else if(modeQueuePort ! = MACH_PORT_NULL && livePort == modeQueuePort) {// This is not waking up from runLoop sleep but jumping from step 5 of runLoop10, Is to process the timer event / / www.jianshu.com/p/ec629063390f CFRUNLOOP_WAKEUP_FOR_TIMER (); 9.1 If a Timer runs out of time, trigger the Timer's callback.if (!__CFRunLoopDoTimers(rl, rlm, mach_absolute_time())) {
                // Re-arm the next timer, because we apparently fired early
                __CFArmNextTimerInMode(rlm, rl);
            }
        }
#endif9.2 If there are blocks sent to main_queue, execute the block commandelse if (livePort == dispatchPort) {
            CFRUNLOOP_WAKEUP_FOR_DISPATCH();
            __CFRunLoopModeUnlock(rlm);
            __CFRunLoopUnlock(rl);
            _CFSetTSD(__CFTSDKeyIsInGCDMainQ, (void *)6, NULL);

            __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__(msg);

            _CFSetTSD(__CFTSDKeyIsInGCDMainQ, (void *)0, NULL);
            __CFRunLoopLock(rl);
            __CFRunLoopModeLock(rlm);
            sourceHandledThisLoop = true;
            didDispatchPortLastTime = true;
        } else{/// 9.3 If a Source1 (port based) event is emitted, process the event CFRUNLOOP_WAKEUP_FOR_SOURCE(); // Despite the name, this worksfor windows handles as well
            CFRunLoopSourceRef rls = __CFRunLoopModeFindSourceForMachPort(rl, rlm, livePort);
            if (rls) {
#if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED || DEPLOYMENT_TARGET_EMBEDDED_MINI
                mach_msg_header_t *reply = NULL;
                sourceHandledThisLoop = __CFRunLoopDoSource1(rl, rlm, rls, msg, msg->msgh_size, &reply) || sourceHandledThisLoop;
                if(NULL ! = reply) { (void)mach_msg(reply, MACH_SEND_MSG, reply->msgh_size, 0, MACH_PORT_NULL, 0, MACH_PORT_NULL); CFAllocatorDeallocate(kCFAllocatorSystemDefault, reply); } // return to __CFRunLoopDoBlocks(rl, RLM);Copy the code

10. Inform the Observer that RunLoop is about to exit. Assign a value to retVal if retVal! = 0 will exit the loop and retVal will be returned.

        if (sourceHandledThisLoop &&stopAfterHandle) {/// return when the loop is finished. retVal = kCFRunLoopRunHandledSource; }else if(timeout_context->termTSR < mach_absolute_time()) {retVal = kCFRunLoopRunTimedOut; }else if(__CFRunLoopIsStopped(rl)) {// external callers forcibly stopped __CFRunLoopUnsetStopped(rl); retVal = kCFRunLoopRunStopped; }else if(RLM ->_stopped) {RLM ->_stopped =false;
            retVal = kCFRunLoopRunStopped;
        } else if (__CFRunLoopModeIsEmpty(rl, rlm, previousMode)) {
            /// source/timer/ Observer lost none retVal = kCFRunLoopRunFinished; } // If there is no timeout, mode is not empty, and loop is not stopped, continue loop.Copy the code

Return to the outer method __CFRunLoopRun call and assign a value to result.

     if(currentMode->_observerMask & kCFRunLoopExit ){ /// 10. Notify Observers: RunLoop is about to exit. __CFRunLoopDoObservers(rl, currentMode, kCFRunLoopExit); }return result;
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CFRunLoopRun ends when result == kCFRunLoopRunStopped && result == kCFRunLoopRunFinished

Complete annotated RunLoop source code

RunLoop flow chart

What does RunLoop do from the entry function?

Core method__CFRunLoopRunWhat did you do?

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Core method`__CFRunLoopRun`What did you do?