iOS Development multithreading-multithreading Technology 1

Last Update:2015-08-09 Source: Internet

Author: User

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I. Basic Concepts 1. What is a processA process is an application that is running in the systemEach application is independent of each otherEach process runs within its proprietary and protected memory Space.2. What is a threadA process that wants to execute a program must need a thread,threads are the basic unit of program execution , and all of the tasks that are applied are executed in the Thread.When the program is started, the system automatically creates a thread for the process, called the "mainthread" "U i thread"3. Thread's seriala thread executes a task serially , that is, within a thread , the execution of the task is performed sequentially from theAt the same time, the thread can only perform one task----> CPU can only execute one thread at a timetwo, multi-threading 1. What is multithreadingMultithreading refers to the creation of multiple threads in the same process, and each thread " concurrently" performs its own tasks.Can effectively improve the efficiency of the systemAs a result, when the CPU quickly switches three threads, it can produce concurrency effects2. The principle of multithreadingAt the same time, the CPU can only execute one thread, and only one thread is executing;When multithreading is concurrent, the CPU is quickly dispatched (switched) between multiple threads, which can produce concurrent (simultaneous) execution Phenomena.note: Concurrent execution is an illusion that appears to be performed concurrently.Parallel is just, is true simultaneous Execution.3. Advantages and disadvantages of multithreadingAdvantages:Can improve the execution efficiency of the programCan improve the utilization of system resources appropriatelyDisadvantagesOpen threads require a certain amount of memory space (default: the main thread 1M sub-thread 512B), If too many threads are turned on, it will consume too much memory space;The more threads, the more consumption of CPU thread scheduling;The more threads, the fewer times each thread is dispatched in the same time;Programming is more complex, such as: communication between threads, data sharing between threads, etc.note: The thread created by the system is called the "main thread", and the other threads are called "child threads".three, multi-threaded Application 1. Main threadThe main thread: when the process is turned on, the system will start by default, which is called: "main thread" or "ui thread";Role:Display/refresh UI InterfaceHandle UI Interface (E.G. click, scroll, drag, etc.)2. Considerations for the main threadFor a better user experience, do not talk about long-time tasks in the main thread, otherwise it will affect the smoothness of the ui, causing the phenomenon of lagFor example:If it takes a long time (10s), then the main thread will remain in the task until the task is completed and when 5s clicks, the User's Click event cannot be immediately answered.Put long-time tasks behind a child thread, enabling immediate user-clicked eventsfour, iOS multi-threading Implementation scheme V. Brief introduction of Pthread and NsthreadA brief introduction to the 1.pthreadThe Created Function:int pthread_create (pthread_t * __restrict, Const pthread_attr_t * __restrict,void * (*) (void *), void * __restrict);pthread_t *restrict: address of the thread identifierConst pthread_attr_t *restrict: Setting the properties of a threadvoid * (*) (void *): a function executed in a thread.void *restrict: The argument passed to the execution Function. Can pass a parameter of any typeThe de void * in the C language is equivalent to the ID in OCReturn Value: 0 on behalf of thread creation succeededReturns the other numeric value that represents the thread creation Failure. the returned value is the failed stateAttention:Under the Arc environment, C language and OC cannot be passed directly__bridge bridging: C language does not have automatic memory management, need to add the C language code automatic memory operation, only in the ARC environment only needOC: There is no need to manually add automatic memory management (retain/release/autorelease/) in the ARC environmentThe purpose of adding is to tell the compiler to add automatic memory management code for the OC CodeTo compile the environment settings for the File:Non-arc Mechanism-fno-objc-arcARC:-fobjc-arcCode:<pre class="brush:objc;gutter:true;"><pre class="brush:objc;gutter:true;">#import "ViewController.h" #import <pthread.h> @interface viewcontroller () @end @implementation viewcontroller-( Void) viewdidload{ [super viewdidload];} -(void) touchesbegan: (nsset*) touches withevent: (uievent*) event{ //create a thread identifier pthread_t myThread; nsstring* str = @ "pthread"; int result = Pthread_create (&mythread, NULL, longtimeoperation, str); NSLog (@ "%d", result); void* (longtimeoperation) (void* data) { NSLog (@ "----%@------%@", data, [nsthread currentthread]); Return NULL;} @end</pre></pre>introduction of 2.NSThread1> Thread creation and startupA nsthread represents this Object.Create a startupNsthread *thread = [[nsthread alloc] initwithtarget:self selector: @selector (run) object:nil];[thread start];When a thread starts, it tells the CPU that it is "ready" and executes the appropriate method when the CPU dispatches the Thread.Automatically start a thread after creating a thread[nsthread detachnewthreadselector: @selector (run) totarget:self withobject:nil];Implicitly creating and starting a thread[self performselectorinbackground: @selector (run) withobject:nil];Tip: The latter two ways to create the thread object cannot be set in more Detail.Common methods of 2>Main Thread-related:+ (nsthread *) mainthread; Get the main thread-(BOOL) ismainthread; is the main thread+ (BOOL) ismainthread; is the main threadGet current Thread:Nsthread *current = [nsthread currentthread];Scheduling Priority for Threads+ (double) threadpriority;+ (BOOL) setthreadpriority: (double) p;-(double) threadpriority;-(BOOL) setthreadpriority: (double) p;The scheduling priority value range is 0.0 ~ 1.0, The default 0.5, the higher the value, the higher the priorityThe name of the thread-(void) setName: (nsstring *) n;-(nsstring *) name;Vi. Status of Threads1, the state of the threadThere are four states in a thread: ready, running, blocking, and Dying.note: When a thread enters a blocking state, it is removed from the scheduler thread pool2. Thread state related methodsStart thread (enter Ready State)-(void) start;Blocking (pausing) a thread (entering blocking State)+ (void) sleepuntildate: (nsdate *) date;+ (void) sleepfortimeinterval: (nstimeinterval) ti;Force stop thread (enter death State)+ (void) exit;seven, the thread lock 1, introduced: thread safety issues (multiple threads access the same piece of Data)。。。。。 Not to be continuediOS Development multithreading-multithreading Technology 1

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