iOS开发笔记4-线程

Posted 2020-06-14

一，创建线程

主线程

    NSThread *current = [NSThread currentThread];

 或

    NSThread *main = [NSThread mainThread];

 

子线程（三种方法）

    NSThread *thread= [[NSThread alloc]initWithTarget:self selector:@selector(run:) object:@"线程A"];

 

    NSThread *thread3 = [NSThread detachNewThreadSelector:@selector(run:) toTarget:self withObject:@"创建完直接启动"];

 

    NSThread *thread3 = [self performSelectorInBackground:@selector(run:) withObject:@"隐式创建"];

 

 

 

二，线程安全隐患

 

以售票为例

#import "ViewController.h"

 

@interface ViewController ()

 

@property (nonatomic,strong)NSThread *thread1;

@property (nonatomic,strong)NSThread *thread2;

@property (nonatomic,strong)NSThread *thread3;

 

@property (nonatomic,assign)int leftTicketCount;

 

@end

 

@implementation ViewController

 

- (void)viewDidLoad {

    [super viewDidLoad];

    

//    默认有10张票

    

    self.leftTicketCount = 10;

    

    

    self.thread1 = [[NSThread alloc]initWithTarget:self selector:@selector(sellTicket) object:nil];

    self.thread1.name = @"售票员1";

    

    self.thread2 = [[NSThread alloc]initWithTarget:self selector:@selector(sellTicket) object:nil];

    self.thread2.name = @"售票员2";

    

    self.thread3 = [[NSThread alloc]initWithTarget:self selector:@selector(sellTicket) object:nil];

    self.thread3.name = @"售票员3";

    

    // Do any additional setup after loading the view, typically from a nib.

}

 

 

-(void)sellTicket

{

    while (1) {

        int count = self.leftTicketCount;

        if (count>0) {

            [NSThread sleepForTimeInterval:0.2];

            self.leftTicketCount = count-1;

            

            NSThread *current = [NSThread currentThread];

            NSLog(@"%@--卖了一张票，还剩%d张票",current,self.leftTicketCount);

            

        }else{

        

            [NSThread exit];

        

        }

    }

 

 

}

 

 

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event

{

    [self.thread1 start];

        [self.thread2 start];

    [self.thread3 start];

}

- (void)didReceiveMemoryWarning {

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}

 

 

 

怎样解决 多个线程调用同一个对象

用互斥锁 如下

-(void)sellTicket

{

    while (1) {

        

        

        @synchronized(self) {

            int count = self.leftTicketCount;

            if (count>0) {

                [NSThread sleepForTimeInterval:0.2];

                self.leftTicketCount = count-1;

                

                NSThread *current = [NSThread currentThread];

                NSLog(@"%@--卖了一张票，还剩%d张票",current,self.leftTicketCount);

                

            }else{

                

                [NSThread exit];

                

            }

        }

 

        }

        

 

}

 

互斥锁的优缺点

优点：能有效防止因多线程抢夺资源造成的数据安全问题

缺点：需要消耗大量的CPU资源

 

互斥锁的使用前提：多条线程抢夺同一块资源 

相关专业术语：线程同步,多条线程按顺序地执行任务

互斥锁，就是使用了线程同步技术

 

 

三，原子性与非原子性

 

OC在定义属性时有nonatomic和atomic两种选择

atomic：原子属性，为setter方法加锁（默认就是atomic）

nonatomic：非原子属性，不会为setter方法加锁

 

atomic加锁原理

@property (assign, atomic) int age;

- (void)setAge:(int)age
{ 

@synchronized(self) { 
_age = age;
}
}

 

原子和非原子属性的选择

nonatomic和atomic对比

atomic：线程安全，需要消耗大量的资源

nonatomic：非线程安全，适合内存小的移动设备

 

四，线程之间的通信

 

线程之间需要用到通信，比如 下载一个图片，线程a需要等到线程b下载好之后再显示出来

以下是例子

//  ViewController.m

//  线程间的通信

//

//  Created by 谢谦 on 16/2/16.

//  Copyright © 2016年 杜苏南. All rights reserved.

//

 

#import "ViewController.h"

 

@interface ViewController ()

@property (nonatomic,weak)IBOutlet UIImageView *iconView;

@end

 

@implementation ViewController

 

- (void)viewDidLoad {

    [super viewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.

}

 

 

 

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event

{

    [self performSelectorInBackground:@selector(download) withObject:nil];

 

 

 

}

 

 

-(void)download

{

    NSURL *url = [NSURL URLWithString:@"fdsf"];

    NSData *data = [NSData dataWithContentsOfFile:url];

    

    

    UIImage *image= [UIImage imageWithData:data];

    

    [self performSelectorOnMainThread:@selector(settingImage:) withObject:image waitUntilDone:NO];

    

 

}

 

-(void)settingImage:(UIImage *)image

{

    self.iconView.image = image;

 

 

}

- (void)didReceiveMemoryWarning {

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}

 

@end

 

 

 

对于   

    [self performSelectorOnMainThread:@selector(settingImage:) withObject:image waitUntilDone:NO];

 有另外两种方法

    [self.iconView performSelector:@selector(settingImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:NO ];

 

    [self.iconView performSelectorOnMainThread:@selector(settingImage:) withObject:image waitUntilDone:NO];