Nsthread of the multithreaded Trilogy

NSThread What is it? ？

As we all know iOS There are four main ways of multithreading development ,NSThread That's one of them .

Here is apple Official explanation

It can be seen that NSThread yes apple A thread class encapsulated , Developers can operate on threads , And you can monitor thread status .
NSThread Is based on thread usage , Lightweight multithreaded programming method （ relative GCD and NSOperation）, One NSThread Object represents a thread

NSThread Use

NSThread The creation of

The creation method of this class is relatively simple , It can be roughly divided into dynamic and static methods .

• 1. You can create... Dynamically ( Example method ) initialization NSThread object , You need to call - (void)start Method to start the thread .

//  Parameter meaning 
/*target selector The object to which the specified message is sent . selector  To send a message to target Selector . This selector must accept only one parameter , And must not have a return value . argument  A single parameter passed to the target . May be nil. */
 NSThread *firstThread = [[NSThread alloc] initWithTarget:self selector:@selector(sellTicket:) object:nil];
    firstThread.name = @"thread1";
    [firstThread start];

• 2. It can also be done through NSThread Static method of ( Class method ) Quickly create and automatically start new threads

//  Detach New Threads , And use the specified selector as the thread entry point .

    [NSThread detachNewThreadSelector:@selector(pressBack:) toTarget:self withObject:@"thread4"];

• 3. Besides NSObject Base class objects also provide implicit quick creation performSelector, Automatically start a new thread

[self performSelectorInBackground:@selector(threadRun) withObject:@"thread5"];

Some threads communicate

 //  The current thread performs an operation 
// [self performSelector:@selector(threadRun)];
// [self performSelector:@selector(threadRun) withObject:@"thread6"];
// //  Delay n Enter the thread in seconds 
// [self performSelector:@selector(threadRun) withObject:@"thread7" afterDelay:2.0];
// //  Specify the main thread operation in other threads 
// [self performSelectorOnMainThread:@selector(threadRun) withObject:nil
// waitUntilDone:YES];
// // （ In the main thread ） Specify another thread to perform the operation 
// [self performSelector:@selector(threadRun) onThread:thread1
// withObject:nil waitUntilDone:YES];
// wait by YES You need to wait for the main thread to operate ,NO The child thread does not have to wait 
// // It is specified here as a thread 
// [self performSelectorInBackground:@selector(threadRun) withObject:nil];
     // This is designated as the background thread 

NSThread Some properties of

A simple example , Ticket handling

Suppose we need to sell 100 movie tickets , We opened three windows at the same time at the ticket office

{
    
//  Thread synchronization problem ：
    NSThread *firstThread = [[NSThread alloc] initWithTarget:self selector:@selector(sellTicket:) object:nil];
    firstThread.name = @"thread1";
    NSThread *secondThread = [[NSThread alloc] initWithTarget:self selector:@selector(sellTicket:) object:nil];
    secondThread.name = @"thread2";
    NSThread *thirdThread = [[NSThread alloc] initWithTarget:self selector:@selector(sellTicket:) object:nil];
    thirdThread.name=@"thread3";
    [firstThread start];
    [secondThread start];
    [thirdThread start];
    [NSThread currentThread];
// while(1) {
    
// NSThread* thread = [[NSThread alloc] initWithTarget:self selector:@selector(sellTicket:) object:nil];
// [thread start];
// }
}
- (void)sellTicket:(NSThread*) thread {
    
    while (self.ticketsCount > 0) {
    
        NSThread *thread = [NSThread currentThread];//  Get the current thread 
        [NSThread sleepForTimeInterval:2];
        self.ticketsCount -- ;
        NSLog(@" Current thread :%@\n The number of votes left is :%d ",thread.name, self.ticketsCount);
   }
}

So let's see what happens , The data will be confused , This is because we have not implemented thread synchronization , It causes competition for resources .

Now we can realize thread synchronization ：

1. The first way @synchronized( object ) Key words are The mutex , When a new thread accesses , If you find that other threads are executing locked code , A new thread enters Sleep .

- (void)sellTicket:(NSThread*) thread {
    
    while (self.ticketsCount > 0) {
    
        @synchronized(self) {
    
        NSThread *thread = [NSThread currentThread];
        [NSThread sleepForTimeInterval:2];
        self.ticketsCount -- ;
        NSLog(@" Current thread :%@\n The number of votes left is :%d ",thread.name, self.ticketsCount);
        }
    }
}

2. You can also use NSLock
   NSLock yes Cocoa Provide us with the most basic lock object , It's also often used , except lock and unlock Outside method ,NSLock It also provides tryLock and lockBeforeDate: Two methods , The previous method tries to lock , If the lock is not available ( It's locked ), It doesn't block threads , Go straight back to NO.lockBeforeDate: Method will be specified in the Date Try locking before , If you cannot lock before the specified time , Then return to NO.

self.threadLock = [[NSLock alloc]init];
while (self.ticketsCount > 0) {
    
        [self.threadLock lock];
        //[self.condition lock];
        NSThread *thread = [NSThread currentThread];
        [NSThread sleepForTimeInterval:2];
        self.ticketsCount -- ;
        NSLog(@" Current thread :%@\n The number of votes left is :%zd ",thread.name, self.ticketsCount);
        [self.threadLock unlock];
        //[self.condition unlock];
    }