多线程（一）

作者: dandelionYD | 来源:发表于2019-04-12 09:26 被阅读0次

面试题

1.你理解的多线程？
2.ios的多线程方案有哪几种？你更倾向于哪一种？
3.你在项目中用过GCD?
4.GCD的队列类型
5.说一下OperationQueue和GCD的区别、以及各自的优势
6.线程安全的处理手段有哪些？
7.OC你了解的锁有哪些？
    - 自旋和互斥对比？
    - 使用以上锁需要注意哪些？
  - 用C/OC/C++，任选其一，实现自旋或互斥？

下面我们来看看几个例子

代码详见 gitHub_Demo

例1

#import "ViewController_1.h"
@interface ViewController_1 ()
@end

@implementation ViewController_1
- (void)viewDidLoad {
    [super viewDidLoad];
    
    //这句代码的本质是往Runloop中添加定时器  如果在主线程，runloop自动开启好了的
    [self performSelector:@selector(test1) withObject:nil afterDelay:.0];//afterDelay-->异步执行的 主队列
    //主队列异步执行时，会先执行完主线程上的代码，然后在主线程上顺序执行任务，不会有新的线程产生，所有任务都是在主线程上完成的
    
    NSLog(@"%@",[NSThread currentThread]);
    
    sleep(1);
    
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_async(queue, ^{
        sleep(2);
        NSLog(@"asyncThread--%@",[NSThread currentThread]);
        NSLog(@"1");
        
        //如果是子线程需要自己手动去启动runloop
        [self performSelector:@selector(test) withObject:nil afterDelay:.0];
        
        //手动去启动runloop
//        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
        
        NSLog(@"3");
    });
    NSLog(@"4");
}

-(void)test{
    NSLog(@"2");
}

-(void)test1{
    NSLog(@"test1Thread---%@",[NSThread currentThread]);
    NSLog(@"test1");
}
@end

打印：
没有手动去启动runloop
Multithreading[17114:917201] <NSThread: 0x600000501400>{number = 1, name = main}
Multithreading[17114:917201] 4
Multithreading[17114:917201] test1Thread---<NSThread: 0x600000501400>{number = 1, name = main}
Multithreading[17114:917201] test1
Multithreading[17114:917255] asyncThread--<NSThread: 0x6000005825c0>{number = 3, name = (null)}
Multithreading[17114:917255] 1
Multithreading[17114:917255] 3

=========================================
手动去启动runloop
Multithreading[17130:918365] <NSThread: 0x600000ef1400>{number = 1, name = main}
Multithreading[17130:918365] 4
Multithreading[17130:918365] test1Thread---<NSThread: 0x600000ef1400>{number = 1, name = main}
Multithreading[17130:918365] test1
Multithreading[17130:918422] asyncThread--<NSThread: 0x600000e712c0>{number = 3, name = (null)}
Multithreading[17130:918422] 1
Multithreading[17130:918422] 2
Multithreading[17130:918422] 3

例2

- (void)test{
    NSLog(@"2");
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSThread *thread = [[NSThread alloc] initWithBlock:^{
        NSLog(@"1"); //一完成任务之后，子线程就退出了
    }];
    [thread start];
    [self performSelector:@selector(test) onThread:thread withObject:nil waitUntilDone:YES];
    NSLog(@"===End====");
}

运行结果：NSLog(@"1") 之后 崩溃了

Multithreading_01.png

- (void)test{
    NSLog(@"2");
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSThread *thread = [[NSThread alloc] initWithBlock:^{
        NSLog(@"1");        
    //一完成任务之后，子线程就退出了
    }];
    
    [thread start];
    
    [self performSelector:@selector(test) onThread:thread withObject:nil waitUntilDone:NO];
    
    sleep(2);
    NSLog(@"===End====");
}
打印：
Multithreading[19178:1044135] 1
Multithreading[19178:1043871] ===End====

Multithreading_02.png

修改崩溃：
- (void)test{
    NSLog(@"2");
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSThread *thread = [[NSThread alloc] initWithBlock:^{
        NSLog(@"1");
        [[NSRunLoop currentRunLoop] addPort:[[NSPort alloc] init] forMode:NSDefaultRunLoopMode];
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
    }];
    
    [thread start];
    [self performSelector:@selector(test) onThread:thread withObject:nil waitUntilDone:YES];
    
    sleep(2);
    NSLog(@"===End====");
}
打印：
Multithreading[19214:1046668] 1
Multithreading[19214:1046668] 2
Multithreading[19214:1046548] ===End====

【开启了runloop后，延长了子线程的生命】
【如果没有，则会执行完任务子线程就退出了】

iOS中的常见多线程方案

Multithreading_03.png

GCD的常用函数

Multithreading_04.png

GCD的队列

Multithreading_05.png

//异步开启子线程，执行任务
-(void)test1{
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
    dispatch_async(queue, ^{
        NSLog(@"%@",[NSThread currentThread]);
        // <NSThread: 0x6000033da280>{number = 3, name = (null)}
    });
}


//同步，在当前线程执行任务
-(void)test2{
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
    dispatch_sync(queue, ^{
        NSLog(@"%@",[NSThread currentThread]);
        // <NSThread: 0x600002442c80>{number = 1, name = main}
    });
}


//同步，在当前线程执行任务（并发无效 ）
-(void)test3{
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
    dispatch_sync(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务1:%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务2:%@",[NSThread currentThread]);
        }
    });
    
    /*
    执行任务1:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务1:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务1:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务1:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务1:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务2:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务2:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务2:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务2:<NSThread: 0x600002b66980>{number = 1, name = main}
    执行任务2:<NSThread: 0x600002b66980>{number = 1, name = main}
     */
}


//异步，开启新线程执行任务（并发）
-(void)test4{
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
    dispatch_async(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务1:%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务2:%@",[NSThread currentThread]);
        }
    });
    
    /*
     执行任务1:<NSThread: 0x6000018ac740>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x6000018ac4c0>{number = 4, name = (null)}
     执行任务1:<NSThread: 0x6000018ac740>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x6000018ac4c0>{number = 4, name = (null)}
     执行任务2:<NSThread: 0x6000018ac4c0>{number = 4, name = (null)}
     执行任务1:<NSThread: 0x6000018ac740>{number = 3, name = (null)}
     执行任务1:<NSThread: 0x6000018ac740>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x6000018ac4c0>{number = 4, name = (null)}
     执行任务1:<NSThread: 0x6000018ac740>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x6000018ac4c0>{number = 4, name = (null)}
     */
}


//串行队列异步执行任务 （按顺序执行）
-(void)test5{
    dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL); //串行队列
    dispatch_async(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务1:%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务2:%@",[NSThread currentThread]);
        }
    });
    /*
     执行任务1:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务1:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务1:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务1:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务1:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     执行任务2:<NSThread: 0x600002de93c0>{number = 3, name = (null)}
     */
}


//在当前线程（此时是主线程），串行执行任务
-(void)test6{
    dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL); //串行队列
    dispatch_sync(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务1:%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务2:%@",[NSThread currentThread]);
        }
    });
    
    /*
     执行任务1:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600000c69400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600000c69400>{number = 1, name = main}
     */
}


//主队列里面异步执行（此时没有开启新的线程）
-(void)test7{
    dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_async(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务1:%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for(int i=0;i<5;i++){
            NSLog(@"执行任务2:%@",[NSThread currentThread]);
        }
    });
    /*
     执行任务1:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务1:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600003d7d400>{number = 1, name = main}
     执行任务2:<NSThread: 0x600003d7d400>{number = 1, name = main}
     */
}

容易混淆的术语

Multithreading_06.png

dispatch_sync和dispatch_async用来控制是否要开启新的线程
 
队列的类型，决定了任务的执行方式（并发、串行）
 1.并发队列
 2.串行队列
 3.主队列（也是一个串行队列）

注意：异步的它不一定 要开启新的线程（只是具备开启新的线程的能力）
主队列里面异步执行任务

只要是sync（同步），或者是在主队列里，他就是在当前线程里面执行任务，那它一定是串行执行任务

没有开启新的线程，那它肯定是串行 执行任务的

各种队列的执行效果

Multithreading_07.png

总结：

Multithreading_08.png

友情链接：

多线程（一）

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