2019獨角獸企業(yè)重金招聘Python工程師標準>>>

一 多線程之間的關(guān)系

2、

二?NSThread

一旦線程停止死亡了，就不能再啟動。所以線程NSThread不能為全局變量

1>.創(chuàng)建和啟動

1.第一種方法：直接創(chuàng)建，手動啟動NSThread?*thread?=?[[NSThread?alloc]?initWithTarget:self?selector:@selector(download：)?object:@"www.baidu.com"];[thread?start];2.第二種方法：創(chuàng)建后立即啟動????[NSThread?detachNewThreadSelector:@selector(download)?toTarget:self?withObject:@"www.baidu.com"];3.第三種方法：隱式創(chuàng)建//主線程[self?performSelector:@selector(download:)?withObject:@"www.baidu.com"];//子線程[self?performSelectorInBackground:@selector(download:)?withObject:@"www.baidu.com"];object是selector方法傳遞的參數(shù) -(void)download:(NSString?*)url {NSLog(@"download--?%@??%@",url,[NSThread?currentThread]); }

2>.睡眠的用法

延遲執(zhí)行不要勇sleep，壞處：卡住主線程 1.第一種[NSThread?sleepForTimeInterval:5.0]; 2.第二種????NSDate?*date?=?[NSDate?dateWithTimeIntervalSinceNow:3.0];[NSThread?sleepUntilDate:date];

3>.強制停止進程

+(void)exit

4>.其他用法

+(NSThread?*)mainThread； +(NSThread?*)currentThread -(BOOL)isMainThread; +(BOOL)isMainThread;

5>.線程間通信

在1個進程中，線程往往不是孤立存在的，多個線程之間需要經(jīng)常進行通信。體現(xiàn)在兩個方面：一，1個線程的數(shù)據(jù)傳遞給另一個線程。二，在1個線程中執(zhí)行完特定任務(wù)后，轉(zhuǎn)到另一個線程繼續(xù)執(zhí)行任務(wù)

-(void)download:(NSString?*)url {NSData?*data?=?[NSData?dataWithContentsOfURL:[NSURL?URLWithString:url]];UIImage?*image?=?[UIImage?imageWithData:data];[self?performSelectorOnMainThread:@selector(pic:)?withObject:image?waitUntilDone:YES]; }-(void)pic:(UIImage?*)image {NSLog(@"pic:%@",image);self.imageView.image?=?image; }-(void)touchesBegan:(NSSet<UITouch?*>?*)touches?withEvent:(UIEvent?*)event {[self?performSelector:@selector(download:)?withObject:@"http://g.hiphotos.baidu.com/image/h%3D200/sign=f23ec3ed1fd8bc3ed90801cab289a6c8/7a899e510fb30f24dc189ad4ce95d143ac4b0362.jpg"]; }

三 GCD

1>線程：同步與異步

同步：只能在當前線程中執(zhí)行任務(wù)，不具備開啟新線程的能力

異步：可以在新的線程中執(zhí)行任務(wù)，具備開啟新線程的能力

2>任務(wù)：并發(fā)與串行

并發(fā)：可以讓多個任務(wù)并發(fā)（同時）執(zhí)行，自動開啟多線程。只有在異步下才有效

串行：讓任務(wù)一個接一個地執(zhí)行

-(void)asyncGlobalQueue {//獲得全局的并發(fā)隊列dispatch_queue_t?queue?=?dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,?0);?//第一個參數(shù)是優(yōu)先級//異步并行。自動創(chuàng)建多條線程dispatch_async(queue,?^{NSLog(@"將任務(wù)放到全局隊列中執(zhí)行?%@",??[NSThread?currentThread]);dispatch_async(queue,?^{NSLog(@"異步并行1?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步并行2?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步并行3?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步并行4?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步并行5?%@",??[NSThread?currentThread]);});}); }-(void)asyncSerialQueue {//異步串行，自動會創(chuàng)建線程，但只開1條dispatch_queue_t?queue?=?dispatch_queue_create("cn.wx",?NULL);dispatch_async(queue,?^{NSLog(@"異步串行1?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步串行2?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步串行3?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步串行4?%@",??[NSThread?currentThread]);});dispatch_async(queue,?^{NSLog(@"異步串行5?%@",??[NSThread?currentThread]);}); }-(void)syncGlobalQueue {dispatch_queue_t?queue?=?dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,?0);//同步并行。不會創(chuàng)建線程，使用主線程dispatch_sync(queue,?^{NSLog(@"同步并行1?%@",??[NSThread?currentThread]);NSLog(@"同步并行2?%@",??[NSThread?currentThread]);NSLog(@"同步并行3?%@",??[NSThread?currentThread]);NSLog(@"同步并行4?%@",??[NSThread?currentThread]);NSLog(@"同步并行5?%@",??[NSThread?currentThread]);}); }-(void)syncSerialQueue {dispatch_queue_t?queue?=?dispatch_queue_create("cn.wx",?NULL);//同步串行。不會創(chuàng)建線程，使用主線程dispatch_sync(queue,?^{NSLog(@"同步并行1?%@",??[NSThread?currentThread]);NSLog(@"同步并行2?%@",??[NSThread?currentThread]);NSLog(@"同步并行3?%@",??[NSThread?currentThread]);NSLog(@"同步并行4?%@",??[NSThread?currentThread]);NSLog(@"同步并行5?%@",??[NSThread?currentThread]);}); }

3>.主隊列

-(void)mainQueue {dispatch_queue_t?queue?=?dispatch_get_main_queue();dispatch_async(queue,?^{NSLog(@"雖然是異步，但是是在主線程執(zhí)行，所以不會開線程");}); //????dispatch_sync(queue,?^{ //????????NSLog(@"不能在串行上使用主隊列，否則會阻塞"); //????});}

4>.線程間通信

????dispatch_queue_t?queue?=?dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,?0);dispatch_async(queue,?^{NSLog(@"子線程進行操作");dispatch_async(dispatch_get_main_queue(),?^{NSLog(@"回主線程加載圖片");});});

5>.延時執(zhí)行

不要使用sleep，會卡住主線程

第一種： [self?performSelector:@selector(down)?withObject:@"abv"?afterDelay:3]; 第二種：dispatch_queue_t?queue?=?dispatch_get_main_queue();dispatch_after(dispatch_time(DISPATCH_TIME_NOW,?(int64_t)(3?*?NSEC_PER_SEC)),?queue,?^{NSLog(@"xx");//回到主線程});dispatch_queue_t?queue?=?dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,?0);dispatch_after(dispatch_time(DISPATCH_TIME_NOW,?(int64_t)(3?*?NSEC_PER_SEC)),?queue,?^{NSLog(@"xx");//回到子線程});

6>.只執(zhí)行一次

????static?dispatch_once_t?onceToken;dispatch_once(&onceToken,?^{NSLog(@"xx");})

四 NSOperation

1>.簡述

先將需要執(zhí)行的操作封裝到一個NSOperation對象，一個對象就相當于GCD的一個block

然后將NSOperation對象添加到NSOperationQueue中

系統(tǒng)會自動將NSOperationQueue中的NSOperation取出來

將取出的NSOperation封裝的操作放到一條線程中執(zhí)行

2>.NSOperation的使用

NSOperation是個抽象類，不具備封裝的能力，必須使用它的子類

1>NSInvocationOperation

????NSInvocationOperation?*operation?=?[[NSInvocationOperation?alloc]?initWithTarget:self?selector:@selector(download)?object:nil];/*[operation?start];?如果直接start，那么將會在當前線程（主線程）同步執(zhí)行*///添加操作到隊列中[queue?addOperation:operation];

2>NSBlockOperation

第一種情況：同步NSBlockOperation?*operation?=?[NSBlockOperation?blockOperationWithBlock:^{NSLog(@"下載一?%@",[NSThread?currentThread]);}];[operation?start];?//?如果直接start，那么將會在當前線程（主線程）同步執(zhí)行第二種情況：異步NSBlockOperation?*operation?=?[[NSBlockOperation?alloc]?init];//operation操作添加多個操作[operation?addExecutionBlock:^{NSLog(@"下載一?%@",[NSThread?currentThread]);}];[operation?addExecutionBlock:^{NSLog(@"下載二?%@",[NSThread?currentThread]);}];[operation?addExecutionBlock:^{NSLog(@"下載三?%@",[NSThread?currentThread]);}];[operation?start];ps：NSBlockOperation還可以直接創(chuàng)建使用對象NSBlockOperation?*operation?=?[NSBlockOperation?blockOperationWithBlock:^{NSLog(@"下載一?%@",[NSThread?currentThread]);}];

3>自定義子類繼承NSOperation

3.NSOperationQueue的使用

1>.基本使用

????//1.創(chuàng)建一個隊列（非主隊列）NSOperationQueue?*queue?=?[[NSOperationQueue?alloc]?init];//設(shè)置最大并發(fā)數(shù)queue.maxConcurrentOperationCount?=?2;//2.創(chuàng)建操作NSBlockOperation?*operation1?=?[NSBlockOperation?blockOperationWithBlock:^{NSLog(@"下載圖片1?--?%@",[NSThread?currentThread]);}];NSBlockOperation?*operation2?=?[NSBlockOperation?blockOperationWithBlock:^{NSLog(@"下載圖片2?--?%@",[NSThread?currentThread]);}];NSInvocationOperation?*operation3?=?[[NSInvocationOperation?alloc]?initWithTarget:self?selector:@selector(down)?object:nil];//操作完后馬上執(zhí)行另一個操作[operation1?setCompletionBlock:^{NSLog(@"下載圖片222");}];//操作依賴,注意不能相互依賴[operation2?addDependency:operation1];[operation3?addDependency:operation2];//3.添加操作到隊列中（自動異步執(zhí)行任務(wù)，并發(fā)）[queue?addOperation:operation1];[queue?addOperation:operation2];[queue?addOperation:operation3];

2>其他用法

????[queue?cancelAllOperations];?//取消隊列的所有操作。也可以直接調(diào)用NSOperation的cancel[queue?setSuspended:YES];?//暫停和恢復隊列。yes為暫停常用場景： -(void)didReceiveMemoryWarning {[super?didReceiveMemoryWarning];[queue?cancelAllOperations]; }-(void)scrollViewWillBeginDecelerating:(UIScrollView?*)scrollView {[queue?setSuspended:YES]; }-(void)scrollViewDidEndDragging:(UIScrollView?*)scrollView?willDecelerate:(BOOL)decelerate {[queue?setSuspended:NO]; }

3>.線程安全

????NSOperationQueue?*queue?=?[[NSOperationQueue?alloc]?init];[queue?addOperationWithBlock:^{//1.異步下載圖片NSURL?*url?=?[NSURL?URLWithString:@"www.baidu.com"];NSData?*data?=?[NSData?dataWithContentsOfURL:url];UIImage?*image?=?[UIImage?imageWithData:data];//2.回到主線程設(shè)置圖片[[NSOperationQueue?mainQueue]?addOperationWithBlock:^{self.imageView.image?=?image;}];}];

五 互斥鎖

????self.obj?=?[[NSObject?alloc]?init];//鎖任意對象，并且需要是唯一一把，所以需要建立個全局變量對象@synchronized(self.obj)?{}

2.atomic:線程安全，需要消耗大量的資源。不建議需要

六 線程注意點

1.不要同時開太多線材（1~3條線材即可，不要超過5條）

2.線程概念

1>主線程：UI線程，顯示、刷新UI界面，處理UI控件的事件

2>子線程：后臺線程，異步線程

3.不要把耗時的操作放在主線程，要放在子線程中執(zhí)行

轉(zhuǎn)載于:https://my.oschina.net/u/2346786/blog/537424

總結(jié)

以上是生活随笔為你收集整理的iOS多线程总结的全部內(nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯，歡迎將生活随笔推薦給好友。