Multithreading Nsoperation and Nsoperationqueue---

Nsoperation and Nsoperationqueue are more powerful abstractions done on a gcd basis, and because of the more gcd use, there are relatively few introductions to them.

1.NSOperation Basic Concepts

The role of 1.NSOperation

• Multithreaded programming is also possible with nsoperation and Nsoperationqueue

2.NSOperation and Nsoperationqueue specific steps to implement multithreading

• Encapsulates the action that needs to be performed into a Nsoperation object
• Then add the Nsoperation object to the Nsoperationqueue
• The system will automatically remove the nsoperation from the Nsoperationqueue
• Put the removed Nsoperation encapsulated operation into a new thread to execute

2. Use 1 specifically. Nsinvocationoperation

Create a Nsinvocationoperation object

- (id)initWithTarget:(id)target selector:(SEL)sel object:(id)arg;

Call the Start method to start the operation

- (void)start;

Once the operation is performed, the Sel method of the target is called

- (void) invocation{//Note: The parent class does not have the ability to encapsulate operations    //1. Encapsulating TasksNsinvocationoperation *OP1 = [[Nsinvocationoperation alloc] Initwithtarget: SelfSelector@selector(Run) object:Nil];//2. To perform a task, you must call start[OP1 start]; Nsinvocationoperation *OP2 = [[Nsinvocationoperation alloc] Initwithtarget: SelfSelector@selector(run2) object:Nil]; [OP2 start];} - (void) run{NSLog(@"%@", [NsthreadCurrentThread]);} - (void) run2{NSLog(@"%@", [NsthreadCurrentThread]);}

Attention:

• By default, when the Start method is called, it does not open a new thread to perform the operation, but instead performs the operation synchronously on the current thread
• Operations are performed asynchronously only if the nsoperation is placed in a nsoperationqueue

2.NSBlockOperation

Create a Nsblockoperation object

+ (id)blockOperationWithBlock:(void (^)(void))block;

Add more actions by Addexecutionblock: method

- (void)addExecutionBlock:(void (^)(void))block;

Note: The operation is performed asynchronously as long as the nsblockoperation encapsulated operand > 1

Code Implementation:-(void) blockoperation{//1. Encapsulating TasksNsblockoperation *OP1 = [Nsblockoperation blockoperationwithblock:^{//Main thread        NSLog(@"1---%@", [NsthreadCurrentThread]); }];//2. Additional Tasks    //Note: In the absence of a queue, if additional tasks are added to Blockoperation, other tasks are executed in the child thread[Op1 addexecutionblock:^{NSLog(@"2---%@", [NsthreadCurrentThread]);    }]; [Op1 addexecutionblock:^{NSLog(@"3---%@", [NsthreadCurrentThread]); }];//3. Start a task[OP1 start];}

3. Custom Nsoperation

1. The steps to customize Nsoperation are simple

• Rewrite-(void) The Main method, where you implement the task you want to perform

2. Override-(void) The note point of the Main method

• Create an auto-free pool yourself (because if it is an asynchronous operation, you cannot access the main thread's auto-free pool)
• Often pass-(BOOL) IsCancelled method detects if the operation is canceled and responds to cancellation

3.NSOperationqueue

The role of 1.NSOperationQueue

• Nsoperation can invoke the Start method to perform a task, but it is performed synchronously by default
• If you add nsoperation to the Nsoperationqueue (action queue), the system automatically executes the operations in Nsoperation asynchronously

2. Add action to Nsoperationqueue

- (void)addOperation:(NSOperation *)op;- (void)addOperationWithBlock:(void (^)(void))block;

Code implementation:

- (void) blockqueue{//1. Create a queueNsoperationqueue *queue = [[Nsoperationqueue alloc] init];//2. Create a taskNsblockoperation *OP1 = [Nsblockoperation blockoperationwithblock:^{NSLog(@"1 = =%@", [NsthreadCurrentThread]);    }]; Nsblockoperation *OP2 = [Nsblockoperation blockoperationwithblock:^{NSLog(@"2 = =%@", [NsthreadCurrentThread]); }];//NOTE: If you are using block to encapsulate a task, there is a much easier way    //As long as the Addoperationwithblock: method is invoked using the queue, the system is automatically encapsulated into a nsblockoperation \And then add it to the queue. [Queue addoperationwithblock:^{NSLog(@"3 = =%@", [NsthreadCurrentThread]); }];//3. Add Task to queue[Queue ADDOPERATION:OP1]; [Queue addoperation:op2];} - (void) invocationqueue{//1. Create a queue    / * What queues are in GCD: Concurrency: Create yourself, Global serial: Create yourself, Home row nsoperationqueue: Main queue: Mainqueue Create yourself: will execute in child threads * /Nsoperationqueue *queue = [[Nsoperationqueue alloc] init];//2. Create a task    //As long as the queue is created by itself, it executes in the child thread    //And the default is concurrent executionNsinvocationoperation *OP1 = [[Nsinvocationoperation alloc] Initwithtarget: SelfSelector@selector(Download1) object:Nil]; Nsinvocationoperation *OP2 = [[Nsinvocationoperation alloc] Initwithtarget: SelfSelector@selector(download2) object:Nil];//3. Adding tasks to the queue    //As soon as the task is added to the queue, the queue automatically calls start[Queue ADDOPERATION:OP1]; [Queue addoperation:op2];} - (void) download1{NSLog(@"1 = =%@", [NsthreadCurrentThread]);} - (void) download2{NSLog(@"2 = =%@", [NsthreadCurrentThread]);}

3. Maximum number of concurrent

1. What is the concurrency number:

• Number of concurrently executed tasks
• For example, open 3 threads at the same time to perform 3 tasks, the concurrency number is 3

2. Correlation method of maximum concurrency number:

- (NSInteger)maxConcurrentOperationCount;- (void)setMaxConcurrentOperationCount:(NSInteger)cnt;

3. Cancellation, suspension, recovery of the queue

1. Cancel all operations on a queue

- (void)cancelAllOperations;

Tip: You can also call the Nsoperation-(void) Cancel method to cancel a single operation

2. Pausing and resuming queues

- (void)setSuspended:(BOOL)b; // YES代表暂停队列，NO代表恢复队列- (BOOL)isSuspended;

4.NSOperation Other usage

1. Operational dependencies

A dependency can be set between 1.NSOperation to guarantee the order of execution
For example, you must let operation a finish, before you can perform operation B, so write

[operationB addDependency:operationA]; // 操作B依赖于操作A

2. You can create a dependency between nsoperation of different queue
3. Note: Do not rely on each other:

• For example a relies on b,b dependency a

4. Monitoring of the operation
Can listen for an operation completed

- (void (^)(void))completionBlock;- (void)setCompletionBlock:(void (^)(void))block;

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Multithreading---nsoperation and nsoperationqueue