OC – > bottom RunLoop

Introduction to the

• As the name implies
  • Operating cycle
  • Do something in a loop while the program is running

• Application category
  • Timer, PerformSelector
  • GCD Async Main Queue
  • Event response, gesture recognition, interface refresh
  • Network request
  • AutoreleasePool

Join without RunLoop

• After line 13, the program is about to exit

The RunLoop

• UIApplicationMain creates a runLoop object
  • If we delete this code and click to open the APP it will immediately flash back.

  

• Pseudocode guesses how this RunLoop works
  • RetVal is always 0 so the program does not exit
  • Let the thread sleep and wait
  • When an event occurs, the program wakes up and handles the event
  • Return 0 and continue the loop without exiting

• The program does not exit immediately, but remains running
• The basic functions of RunLoop
  • Keep the program running
  • Handle various events in the App (such as touch events, timer events, etc.)
  • Save CPU resources, improve program performance: work when you should work, rest when you should rest
  • .

RunLoop object

• IOS has two sets of apis to access and use RunLoop
  • Foundation: NSRunLoop
  • The Core Foundation: CFRunLoopRef
• Both NSRunLoop and CFRunLoopRef represent RunLoop objects
  • NSRunLoop is a layer of OC wrapper based on CFRunLoopRef
  • CFRunLoopRef is open source
  • Opensource.apple.com/tarballs/CF… download

  

RunLoop with thread

• Each thread has a unique RunLoop object corresponding to it
• Runloops are stored in a global Dictionary, with threads as keys and runloops as values

• The thread is created without a RunLoop object; the RunLoop is created the first time it gets it
• The RunLoop is destroyed at the end of the thread
• The RunLoop for the main thread is automatically acquired (created), and RunLoop is not enabled for the child thread by default
  • UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class])); This can be interpreted as no runloop when the main thread was created, but it was called at the same time[NSRunLoop currentRunLoop]Actively get (create) a runloop for the main thread.

Get the RunLoop object

• Foundation

  • [NSRunLoop currentRunLoop]; // Get the RunLoop object for the current thread
  • [NSRunLoop mainRunLoop]; // Get the main thread RunLoop object

• Core Foundation

  • CFRunLoopGetCurrent(); // Get the RunLoop object for the current thread
  • CFRunLoopGetMain(); // Get the main thread RunLoop object

• The source code to explore

  

  • 1. Runloop returns the key from the dictionary based on the thread
  • 2. Add a newloop to the dictionary if the loop is empty

Runloop-related classes

• Five classes for RunLoop in Core Foundation
  • CFRunLoopRef
  • CFRunLoopModeRef
  • CFRunLoopSourceRef
  • CFRunLoopTimerRef
  • CFRunLoopObserverRef
• Simplify what works
  • So one runloop per thread
  • CFMutableSetRef: Collections are arrays but arrays are ordered and collections are unordered
  • _modes: Data loaded in the modes are CFRunLoopModeRef
  • _currentMode: indicates the current mode
  • Runloop has a number of modes in the modes, but only one mode is considered currentMode.

  

  • _NAME: indicates the name of the schema
  • 4 set
  • _sources0 and _source1 are collection objects of CFRunLoopSourceRef
  • _observers is a collection object for CFRunLoopObserverRef
  • _timers is the collection object for CFRunLoopTimerRef

CFRunLoopModeRef

• CFRunLoopModeRef indicates the running mode of RunLoop

• A RunLoop contains several Mode, each Mode and contains several Source0 / Source1 / Timer/Observer

• Only one of these modes can be selected as currentMode when RunLoop starts

• If you need to switch Mode, you can only exit the current Loop, and select another Mode to enter the program will not exit.

  • Different groups of Source0 / Source1 / Timer/Observer can be separated, each other

• If there is no any Source0 / Source1 / Timer Mode/Observer, RunLoop immediately exit

• Two common modes

  • KCFRunLoopDefaultMode (NSDefaultRunLoopMode) : The default Mode of the App, in which the main thread usually runs
    • The default mode of runloop
  • UITrackingRunLoopMode: interface tracing Mode, used by ScrollView to track touch sliding, ensuring that the interface sliding is not affected by other modes
    • Runloop sliding mode

CFRunLoopObserverRef

Add an Observer to listen for all RunLoop states

The running logic of RunLoop

• Source0
  • Touch event handling
  • performSelector:onThread:
• Source1
  • Port-based communication between threads
  • System Event Capture
• Timers
  • NSTimer
  • performSelector:withObject:afterDelay:
• Observers
  • Used to listen for the status of RunLoop
  • UI refresh (BeforeWaiting)
  • Autorelease Pool (BeforeWaiting)
• 01. Notify Observers: enter Loop
• Observers: They are about to deal with Timers
• Observers: Intentions to deal with Sources
• 04, Process Blocks
• 05, processing Source0 (possibly processing Blocks again)
• 06, If Source1 exists, go to Step 8
• 30, Notifying Observers that they are about to start hibernating.
• 30, notifying Observers that they are astounded by a message.
  • 01 > deal with the Timer
  • 02> Handle GCD Async To Main Queue
  • 3 > deal with Source1
• 09. Process Blocks
• 10. According to the previous results, decide what to do
  • 01> Return to Step 02
  • 02 > exit the Loop
• Observers: exit Loop

My understanding by analogy this is my understanding can not be used as a reference.

• In layman’s terms, a runloop is a machine that has various modes.
• Each mode has four arrays, like four knobs. The 4 knobs do not affect each other and can be customized by adjusting the knobs.
• When you want to start the machine, you should first select a mode and run the machine as the current mode. To switch the mode, you should stop the current mode first.
• If you select a mode where all four knobs are 0, the machine shuts down automatically and goes into a sleep state waiting for the event to activate.
• The fourth knob can not only control the machine to perform certain actions, but also monitor the state of the machine
• What a loop in a runloop does
  • To enter a mode, remove source0, source1, timers, and Observer from the mode

Source code analysis

SInt32 CFRunLoopRunSpecific(CFRunLoopRef rl, CFStringRef modeName, CFTimeInterval seconds, Boolean returnAfterSourceHandled) {/* DOES CALLOUT */ // notify observers: Loop __CFRunLoopDoObservers(rL, currentMode, kCFRunLoopEntry); / / to do specific result = __CFRunLoopRun (rl, currentMode, seconds, returnAfterSourceHandled, previousMode); // Notify obsercers: Exit Loop __CFRunLoopDoObservers(RL, currentMode, kCFRunLoopExit); return result; } /* rl, rlm are locked on entrance and exit */ static int32_t __CFRunLoopRun(CFRunLoopRef rl, CFRunLoopModeRef rlm, CFTimeInterval seconds, Boolean stopAfterHandle, CFRunLoopModeRef previousMode) { uint64_t startTSR = mach_absolute_time(); int32_t retVal = 0; Do {// Notify obsercers that timers __CFRunLoopDoObservers(RL, RLM, kCFRunLoopBeforeTimers) are about to be processed; // Notify obsercers: sources __CFRunLoopDoObservers(RL, RLM, kCFRunLoopBeforeSources) will be processed; // Notify obsercers that block __CFRunLoopDoBlocks(rL, RLM) is about to be processed; // Handle sources0 if (__CFRunLoopDoSources0(rl, RLM, stopAfterHandle)) {// Handle block __CFRunLoopDoBlocks(rl, RLM); } Boolean poll = sourceHandledThisLoop || (0ULL == timeout_context->termTSR); If (__CFRunLoopServiceMachPort(dispatchPort, &msg, sizeof(msg_buffer), &livePort, 0, &voucherState, NULL)) {// if there is source1, goto handle_msg goto handle_msg; }} // Notify Observers: about to hibernate __CFRunLoopDoObservers(rl, RLM, kCFRunLoopBeforeWaiting); // Start sleeping __CFRunLoopSetSleeping(rl); CFAbsoluteTime sleepStart = poll ? 0.0: CFAbsoluteTimeGetCurrent (); __CFRunLoopServiceMachPort(waitSet, &msg, sizeof(MSg_buffer), &livePort, poll? 0 : TIMEOUT_INFINITY, &voucherState, &voucherCopy); / / wake __CFRunLoopUnsetSleeping (rl); // Notify the observer: hibernate __CFRunLoopDoObservers(rl, RLM, kCFRunLoopAfterWaiting); handle_msg:; // Handle timers __CFRunLoopDoTimers(rl, RLM, Mach_absolute_time ()))} else if (be awakened by GCD) {// Handle GCD __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__(MSG); } else {//source1 __CFRunLoopDoSource1(rl, RLM, RLS, MSG, MSG ->msgh_size, &reply) || sourceHandledThisLoop; } // Handle block __CFRunLoopDoBlocks(rl, RLM); / / set the return value 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; }Copy the code

RunLoop executes the flow

Implementation principle of RunLoop hibernation

• Wait for another message to wake up the current thread to sleep: blocked threads no longer go down
• Unlike while (1), which blocks, such a thread does not really rest

__CFRunLoopServiceMachPort(waitSet, &msg, sizeof(msg_buffer), &livePort, poll ? 0 : TIMEOUT_INFINITY, &voucherState, &voucherCopy);

• This is the kernel-level API that allows threads to hibernate and send messages to the kernel-level CPU to rest and save power.
• All we can control is the API at the page level

RunLoop applications in the real world

• Control the thread lifecycle (thread survival)
• Fixed NSTimer stopping working when sliding
• Monitoring application lag
• Performance optimization

Application 1 solves the problem that NSTimer stops working when sliding

• 1. Create a timer

• Put a textView

• And it turns out that the timer stops when we drag the textView
• The principle of analysis
  • Runloop can only run in one mode at a time.
  • The timer is not in drag mode and works in default mode.
  • If the timer is in drag mode, it can run.
• Put the timer in drag mode as well as NSRunLoopCommonModes in default mode
• ScheduledTimerWithTimeInterval this method will default to the timer in the default mode

- (void)viewDidLoad { [super viewDidLoad]; static int count = 0; NSTimer * timer = [NSTimer timerWithTimeInterval: 1.0 repeats: YES block: ^ (NSTimer * _Nonnull timer) {NSLog (@ "% d", ++count); }]; // [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode]; // [[NSRunLoop currentRunLoop] addTimer:timer forMode:UITrackingRunLoopMode]; // NSDefaultRunLoopMode, UITrackingRunLoopMode are real modes. It's just a tag / / timer can work under _commonModes stored in the array patterns [[NSRunLoop currentRunLoop] addTimer: timer forMode: NSRunLoopCommonModes]; / / [NSTimer scheduledTimerWithTimeInterval: 1.0 repeats: YES block: ^ (NSTimer * _Nonnull timer) {/ / NSLog (@ "% d", ++count); // }]; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } @endCopy the code