（IOS）多线程开发

一、线程的使用

以向网络请求一张图片为例

-(void)downURL:(NSURL *)aURL

{

    NSData *d = [NSData dataWithContentsOfURL:aURL];

    UIImage *img = [UIImage imageWithData:d];

    //imgView.image = img;

    // 切换回主线程执行UI的操作

    [imgView performSelectorOnMainThread:@selector(setImage:) withObject:img waitUntilDone:NO];

}

方法1：系统后台执行

[self performSelectorInBackground:@selector(downURL:) withObject:url];

方法2：利用C级的NSThread执行

[NSThread detachNewThreadSelector:@selector(downURL:) toTarget:self withObject:url];    // 分派线程执行一个方法，静态方法创建了线程，并开始执行

NSThread *t1 = [[NSThread alloc] initWithTarget:self selector:@selector(downURL:) object:url];

[t1 start];     // 创建具体线程对象需要触发开始

方法3：利用OC级的NSOperation执行，此处使用的是NSOperation的子类NSInvocationOperation（或NSBlockOperation）去执行，因为NSOperation只是一个抽象类，不能直接实例化使用

NSInvocationOperation *op1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(downURL:) object:url];

[op1 setQueuePriority:NSOperationQueuePriorityNormal]

NSInvocationOperation *op2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(downURL:) object:url];

//[op1 start];   // 线程对象不放到队列中的话需要触发开始

queue = [[NSOperationQueue alloc] init];

queue.maxConcurrentOperationCount = ;  // 设置队列同时执行线程最大数

[queue addOperation:op1];   // 队列会自动打开线程

[queue addOperation:op2];

[op1 release];

[op2 release];

方法4：继承NSOperation自定义线程类，利用target-action机制

-(void)someMethod

{

    BIDImageOperation *op = [[BIDImageOperation alloc] initWithTarget:self Selector:@selector(refreshUI:) URL:url1];

    [op start];

    // [op release];

}

-(void)refreshUI:(UIImage *)aImg

{

    [imgView performSelectorOnMainThread:@selector(setImage:) withObject:aImg waitUntilDone:NO];

}

using

#import <Foundation/Foundation.h>

@interface BIDImageOperation : NSOperation

{

    NSString *_imgURL;

    id _target;

    SEL _action;

}

@property (nonatomic,retain) NSString *imgURL;

@property (nonatomic,assign) id target;

@property (nonatomic,assign) SEL action;

-(id)initWithTarget:(id)aTarget Selector:(SEL)aSelector URL:(NSString *)aURL;

@end

######################################

#import "BIDImageOperation.h"

@implementation BIDImageOperation

@synthesize imgURL = _imgURL,target = _target,action = _action;

-(id)initWithTarget:(id)aTarget Selector:(SEL)aSelector URL:(NSString *)aURL

{

    if (self = [super init]) {

        self.imgURL = aURL;

        self.target = aTarget;

        self.action = aSelector;

    }

    return self;

}

-(void)main

{

    if ([self isCancelled]) {

        return;

    }

    NSURL *url = [NSURL URLWithString:self.imgURL];

    NSData *data = [NSData dataWithContentsOfURL:url];

    UIImage *img = [UIImage imageWithData:data];

    if ([self isCancelled]) {

        return;

    }

    [self.target performSelector:self.action withObject:img];

}

@end

custom thread

二、线程安全

以一个售票服务的程序为例

1.锁

-(void)someMethod

{

    NSThread *t1 = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];

    t1.name = @"window1";

    [t1 start];

    NSThread *t2 = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];

    t2.name = @"window2";

    [t2 start];

    //[NSThread detachNewThreadSelector:@selector(saleTicket) toTarget:self withObject:nil];

}

-(void)saleTicket

{

    while ()

    {

        [lock lock];   // 对可能出现互斥的变量设置部分进行锁定

        if (count>)

        {

            count =  - ticket;

            NSLog(@"%@ 卖出：%d 剩余：%d",[NSThread currentThread].name,ticket,count);

            ticket++;

        } else {

            [lock unlock];

            break;

        }

        [lock unlock];

    }

}

2.取消

[op cancel];并不能将线程取消掉，因为该方法是建议关闭而已，除非线程里的main或调用的方法中有对这个建议做接受处理，如下

if ([self isCancelled]) // or  if([op isCancelled])

{

     return;

}

在dealloc方法中，自定义线程类的成员变量都应该添加[op cancel];，队列则需要添加[queue cancelAllOperations];来停止退出线程。

巴特西

（IOS）多线程开发

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