Objective-c Multithreading

iOS has three multithreaded technologies:

• 1.NSThread
  • Created in two ways:
    • 1. Instance method:
    • -(ID) Initwithtarget: (ID) Target selector: (SEL) Selector object: (ID) argument
    • You can set thread information such as thread priority before you run a thread operation by creating a thread object before you run the thread action
    • 2. Class method:
    • + (void) Detachnewthreadselector: (SEL) Aselector Totarget: (ID) atarget withobject: (ID) anargument
    • create thread directly and start running thread
    • usage Example:
      • [Nsthread detachnewth Readselector: @selector (dosomething:) totarget:self Withobject:nil];
      • nsthread* myThread = [[Nsthread alloc] initwithtarget:self selector: @selector (dosomething:) Object:nil];
      • [MyThread start];
    • parameter explanation:
    • Selector: The method that the thread executes, the selector can have only one parameter, and cannot have a return value.
    • target:selector The object sent by the message
    • argument: The only parameter that is transmitted to target, or nil
    • does not show the method of creating the thread:
    • Call NSObject class method Performselectorinbackground:withobject: The
    • demonstration is performed by default in a child thread:
      • [OBJ Performselectorinbackgro und: @selector (dosomething) Withobject:nil];
    • Demonstration Example: (Sub-thread asynchronous download, main thread UI update)

#import "ViewController.h"#defineKurl @ "http://avatar.csdn.net/2/c/d/1_totogo2010.jpg "@interfaceViewcontroller ()@end@implementationViewcontroller- (void) Viewdidload{[super Viewdidload];//[Nsthread detachnewthreadselector: @selector (downloadimage:) totarget:self Withobject:kurl];Nsthread *thread = [[Nsthread alloc]initwithtarget:self selector: @selector (downloadimage:)Object: Kurl]; [Thread start];}-(void) Downloadimage: (NSString *) Url{nsdata*data =[[NSData alloc] Initwithcontentsofurl:[nsurl Urlwithstring:url]]; UIImage*image =[[UIImage alloc]initwithdata:data];if(Image = =Nil) {}Else{[Self performselectoronmainthread: @selector (updateUI:) withobject:image Waituntildone:yes];//execute (inter-thread communication) in the main thread}}-(void) UpdateUI: (uiimage*) Image{self.imageview.image=image;}@end

• 2.NSOperation
  • To encapsulate the independent unit of work in the execution program, providing an asynchronous execution mechanism.
  • Nsoperation class as abstract class, based on template method design pattern
  • The operations can be run independently or in conjunction with the Operation queue.
  • There are two ways of using it:
    • 1. Use a defined two subclass: Nsinvocationoperation and Nsblockoperation.
    • Nsinvocationoperation:
      • How to create:
      • nsinvocationoperation* operation = [[Nsinvocationoperation alloc]initwithtarget:self selector: @selector ( Customtaskmethod:) Object:params];
    • Nsblockoperation:
      • How to create:
      • nsblockoperation* blockoperation = [nsblockoperation blockoperationwithblock: ^{
      • To do the task.
      • }];
    • After creating the blockoperation, you can call Addexecutionblock: method to add more block
    • Demonstration examples:

#import "ViewController.h"#defineKurl @ "http://avatar.csdn.net/2/c/d/1_totogo2010.jpg "@interfaceViewcontroller ()@end@implementationViewcontroller- (void) Viewdidload{[super Viewdidload]; Nsinvocationoperation*operation =[[Nsinvocationoperation alloc]initwithtarget:selfselector: @selector (downloadimage:)Object: Kurl]; Nsoperationqueue*queue =[[Nsoperationqueue alloc]init]; [Queue addoperation:operation];//additional setup after loading the view, typically from a nib.}-(void) Downloadimage: (NSString *) Url{nslog (@"url:%@", URL); Nsurl*nsurl =[Nsurl Urlwithstring:url]; NSData*data =[[NSData Alloc]initwithcontentsofurl:nsurl]; UIImage* Image =[[UIImage Alloc]initwithdata:data]; [Self Performselectoronmainthread: @selector (updateUI:) withobject:image waituntildone:yes];}-(void) UpdateUI: (uiimage*) Image{self.imageview.image=image;}

• • • 2. Inheriting nsoperation
      • 1. Provide a custom initialization method that provides the initialization process before executing operation, prepares the Operation state
      • 2. Just inherit one method of overriding Nsoperation main
      • 3. Then put the object of the Nsoperation subclass into the Nsoperationqueue queue and the queue will start and start processing it
      • Demonstration examples:

@interfacemovefileoperation:nsoperation- (ID) Initwithsrcurl: (Nsurl *) Srcurl Todestinationurl: (nsurl*) Desurl;@end//movefileoperation.m@interfacemovefileoperation () @property (retain) Nsurl*Srcurl, @property (retain) Nsurl*Desurl;@end@implementationmovefileoperation@synthesizeRooturl, queue;- (ID) Initwithsrcurl: (Nsurl *) Srcurl Todestinationurl: (nsurl*) Desurl; { Self=[Super init];if(self) {Self.srcurl=Srcurl;self.desurl=Desurl;}returnSelf ;}- (void) main{if([self iscancelled]) {return;} Nsdirectoryenumerator*itr =[[Nsfilemanager Defaultmanager] EnumeratorAtURL:self.srcURL includingpropertiesforkeys:niloptions: ( Nsdirectoryenumerationskipshiddenfiles|nsdirectoryenumerationskipspackagedescendants) Errorhandler:nil]; Nserror*error = [NserrorNew]; for(Nsurl *urlinchITR) {if([self iscancelled]) {// Break; }Else{nsstring*filename =[url lastpathcomponent]; Nsurl*desfileurl =[Self.desurl Urlbyappendingpathcomponent:filename]; [[Nsfilemanager Defaultmanager] copyitematurl:url tourl:desfileurl error:&ERROR];} }}

• • • • The operation support thread cancellation behavior through the IsCancelled method:
      • The common locations for correctly calling iscancelled include:
        • 1. Before the actual implementation of the work
        • 2. In each loop of the actuator, if a single execution takes a long time to add the number of calls as appropriate
        • 3. Code where the program is relatively easy to terminate.
      • To configure Operation dependencies:
        • Call the Adddependency: method to establish a dependency relationship between the two Operation objects:
        • This one-way relationship indicates that the current operation object cannot be executed until the target operation object finishes executing.
        • The dependency of the Operation object is not limited to the same operation queue.
        • Operation objects that have dependencies can be added to different operations queues.
        • However, you cannot add circular dependencies between operation.
      • Add Completion Block:
        • The Setcompletionblock: method allows you to complete the work of adding completion block, where you can distribute operation completed messages.
      • How to execute Operation:
        • 1. Add the Operation object to the Operations queue Nsoperatinqueue object:
          • nsoperationqueue* aqueue = [[NSO Perationqueue alloc] init];
          • 1.//Add A single operation
          • [Aqueue Addoperation:anop];
          • 2.//ADD Multiple operations
          • [Aqueue addoperations:anarrayofops waituntilfinished:no];
          • 3.//ADD a block
          • [Aqueue addoperationwithblock:^{
          • /* do something. */
          • }];
          The
          • Nsoperationqueue is designed to be used concurrently to execute the Operation,setmaxconcurrentoperationcount: method to set the maximum number of operations queue execution in parallel. The
          • needs to set dependencies between operation to ensure that the order in which they are executed is what you want.
        • 2. Manual execution of operation:
          • A operation is considered to be operational only if its IsReady method returns YES. The
          • IsReady method is integrated into the Nsoperation dependency management system to ensure operation dependency status.
          • operation only starts running when the dependencies are clear. When
          • executes operation manually, its Start method must be called.
      • Cancel Operation:
        • Once the operation queue is joined, the operation queue has the operation and it cannot be deleted.
        • The only way to bring up operation is to cancel it (cancel)
        • A operation on a cancel can cancel its execution, and calling Cancelalloperations on the action queue object cancels all operation.
        • Operation's cancellation behavior is also considered complete (finished), and other operation objects that depend on it receive a KVO notification to clear the dependency.
      • Wait for operation to end:
        • If the process that creates the operation needs to handle the operation results, you can use the Nsoperation Waituntilfinished method to block code until operation is complete (never wait for a operation to end on the main thread)
      • To suspend and reply to a queue:
        • Call the setsuspended: Method of the Nsoperationqueue object to manipulate the queue to suspend. Suspending a queue does not hinder the operation that is currently executing, it simply blocks the execution of the new operation.
• 3.GCD

Objective-c Multithreading