iOS学习笔记4-线程
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];
