线程间的通信
简单说明
线程间通信:在1个进程中,线程往往不是孤立存在的,多个线程之间需要经常进行通信
线程间通信的体现
1个线程传递数据给另1个线程
在1个线程中执行完特定任务后,转到另1个线程继续执行任务
线程间通信常用方法
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait; - (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait;
// // YYViewController.m // 06-NSThread04-线程间通信 // // Created by apple on 14-6-23. // Copyright (c) 2014年 itcase. All rights reserved. //#import "YYViewController.h" @interface YYViewController () @property (weak, nonatomic) IBOutlet UIImageView *iconView; @end
@implementation YYViewController- (void)viewDidLoad { [super viewDidLoad]; }
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
// 在子线程中调用download方法下载图片 [self performSelectorInBackground:@selector(download) withObject:nil]; }
-(void)download { //1.根据URL下载图片 //从网络中下载图片 NSURL *urlstr=[NSURL URLWithString:@"fdsf"];
//把图片转换为二进制的数据 NSData *data=[NSData dataWithContentsOfURL:urlstr];//这一行操作会比较耗时
//把数据转换成图片 UIImage *image=[UIImage imageWithData:data]; //2.回到主线程中设置图片 [self performSelectorOnMainThread:@selector(settingImage:) withObject:image waitUntilDone:NO]; }
//设置显示图片 -(void)settingImage:(UIImage *)image { self.iconView.image=image; }
@end
// // YYViewController.m // 06-NSThread04-线程间通信 // // Created by apple on 14-6-23. // Copyright (c) 2014年 itcase. All rights reserved. //#import "YYViewController.h" #import <NSData.h>
@interface YYViewController () @property (weak, nonatomic) IBOutlet UIImageView *iconView; @end
@implementation YYViewController- (void)viewDidLoad { [super viewDidLoad]; }
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { // 在子线程中调用download方法下载图片
[self performSelectorInBackground:@selector(download) withObject:nil]; }
-(void)download {
//1.根据URL下载图片 //从网络中下载图片 NSURL *urlstr=[NSURL URLWithString:@"fdsf"];
//把图片转换为二进制的数据 NSData *data=[NSData dataWithContentsOfURL:urlstr];//这一行操作会比较耗时
//把数据转换成图片 UIImage *image=[UIImage imageWithData:data];
//2.回到主线程中设置图片 //第一种方式 // [self performSelectorOnMainThread:@selector(settingImage:) withObject:image waitUntilDone:NO];
//第二种方式 // [self.imageView performSelector:@selector(setImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:NO];
//第三种方式 [self.iconView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:NO]; }
//设置显示图片 //-(void)settingImage:(UIImage *)image //{ // self.iconView.image=image; //}
@end
线程安全
一、多线程的安全隐患
资源共享
1块资源可能会被多个线程共享,也就是多个线程可能会访问同一块资源
比如多个线程访问同一个对象、同一个变量、同一个文件
当多个线程访问同一块资源时,很容易引发数据错乱和数据安全问题
示例一:
示例二:
问题代码:
// // YYViewController.m // 05-线程安全 // // Created by apple on 14-6-23. // Copyright (c) 2014年 itcase. All rights reserved. //#import "YYViewController.h"
@interface YYViewController () //剩余票数
@property(nonatomic,assign) int leftTicketsCount; @property(nonatomic,strong)NSThread *thread1; @property(nonatomic,strong)NSThread *thread2; @property(nonatomic,strong)NSThread *thread3;
@end
@implementation YYViewController- (void)viewDidLoad { [super viewDidLoad];
//默认有20张票
self.leftTicketsCount=10;
//开启多个线程,模拟售票员售票
self.thread1=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
self.thread1.name=@"售票员A";
self.thread2=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
self.thread2.name=@"售票员B";
self.thread3=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil]; self.thread3.name=@"售票员C"; }
-(void)sellTickets { while (1) { //1.先检查票数 int count=self.leftTicketsCount; if (count>0) { //暂停一段时间 [NSThread sleepForTimeInterval:0.002];
//2.票数-1 self.leftTicketsCount= count-1; //获取当前线程 NSThread *current=[NSThread currentThread]; NSLog(@"%@--卖了一张票,还剩余%d张票",current,self.leftTicketsCount); }else { //退出线程 [NSThread exit]; } } }
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { //开启线程
[self.thread1 start]; [self.thread2 start]; [self.thread3 start];
}
@end
二、安全隐患分析
三、如何解决
互斥锁使用格式
@synchronized(锁对象) { // 需要锁定的代码 }
注意:锁定1份代码只用1把锁,用多把锁是无效的
代码示例:
// // YYViewController.m // 05-线程安全 // // Created by apple on 14-6-23. // Copyright (c) 2014年 itcase. All rights reserved. //#import "YYViewController.h"
@interface YYViewController ()
//剩余票数 @property(nonatomic,assign) int leftTicketsCount; @property(nonatomic,strong)NSThread *thread1; @property(nonatomic,strong)NSThread *thread2; @property(nonatomic,strong)NSThread *thread3; @end
@implementation YYViewController
- (void)viewDidLoad { [super viewDidLoad]; //默认有20张票 self.leftTicketsCount=10; //开启多个线程,模拟售票员售票
self.thread1=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
self.thread1.name=@"售票员A";
self.thread2=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
self.thread2.name=@"售票员B";
self.thread3=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
self.thread3.name=@"售票员C"; }
-(void)sellTickets { while (1) { @synchronized(self){//只能加一把锁 //1.先检查票数
int count=self.leftTicketsCount; if (count>0) { //暂停一段时间 [NSThread sleepForTimeInterval:0.002]; //2.票数-1
self.leftTicketsCount= count-1; //获取当前线程 NSThread *current=[NSThread currentThread]; NSLog(@"%@--卖了一张票,还剩余%d张票",current,self.leftTicketsCount);
}else { //退出线程 [NSThread exit]; } } } }
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
//开启线程 [self.thread1 start]; [self.thread2 start]; [self.thread3 start]; }
@end
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
四:原子和非原子属性
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; } }
iOS开发的建议
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