同步只能在当前线程中执行任务,不具备开启新线程的能力。异步可以在新线程中执行任务,具备开启新线程的能力。
多线程:一个进程可以开启多条线程,每条线程可以执行不同的任务。实质上在同一时间,CPU只能处理一条线程,CPU快速在多线程间调度,产生并发执行假象。
多线程实例应用
-(void)test06
{
#异步主队列: 异步不会阻塞主线程 主队列任务必须放在主线程执行
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"%@--A",[NSThread currentThread]);
});
#第一步: 主线程执行 输出B
NSLog(@"%@--B",[NSThread currentThread]);
dispatch_queue_t queue=dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
#同步全局并发队列: 同步会阻塞主线程 第二步: 输出C
dispatch_sync(queue, ^{
NSLog(@"%@--C",[NSThread currentThread]);
});
#异步全局并发队列: 开启新线程执行任务 未阻塞主线程
dispatch_async(queue, ^{
NSLog(@"%@--D",[NSThread currentThread]);
});
#异步主队列: 异步不会阻塞主线程 主队列任务必须放在主线程执行
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"%@--E",[NSThread currentThread]);
});
#此方法主线程执行 相当于异步主队列
[self performSelector:@selector(testMethod) withObject:nil afterDelay:0];
#第三步: 主队列执行 输出F
NSLog(@"%@--F",[NSThread currentThread];
/*
主队列任务顺序: G->E->A
输出结果为:
B C F D A E G
*/
}
-(void)testMethod{
NSLog(@"%@--G",[NSThread currentThread]);
}
#打印结果
{number = 1, name = main}--B
{number = 1, name = main}--C
{number = 1, name = main}--F
{number = 3, name = (null)}--D
{number = 1, name = main}--A
{number = 1, name = main}--E
{number = 1, name = main}--G
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
[self test01];
[self test02];
[self test03];
[self test04];
[self test05];
}
-(void)test05{
NSOperationQueue *queue=[[NSOperationQueue alloc] init];
NSBlockOperation *operationA=[NSBlockOperation blockOperationWithBlock:^{
NSLog(@"%@--下载第A张图片",[NSThread currentThread]);
}];
NSBlockOperation *operationB=[NSBlockOperation blockOperationWithBlock:^{
NSLog(@"%@--下载第B张图片",[NSThread currentThread]);
}];
NSBlockOperation *operationC=[NSBlockOperation blockOperationWithBlock:^{
NSLog(@"%@--下载第C张图片",[NSThread currentThread]);
}];
# [queue addOperation:operationA];
# [queue addOperation:operationB];
# [queue addOperation:operationC];
#设置依赖 按需求A B C 顺序执行
[operationB addDependency:operationA];
[operationC addDependency:operationB];
#添加任务到队列
[queue addOperation:operationA];
[queue addOperation:operationB];
[queue addOperation:operationC];
}
-(void)test04{
NSOperationQueue *queue=[[NSOperationQueue alloc] init];
#设置最大并发数
# queue.maxConcurrentOperationCount=1;
NSBlockOperation *operation1=[NSBlockOperation blockOperationWithBlock:^{
NSLog(@"%@--下载第一张图片",[NSThread currentThread]);
}];
NSBlockOperation *operation2=[NSBlockOperation blockOperationWithBlock:^{
NSLog(@"%@--下载第二张图片",[NSThread currentThread]);
}];
NSBlockOperation *operation3=[NSBlockOperation blockOperationWithBlock:^{
NSLog(@"%@--下载第三张图片",[NSThread currentThread]);
}];
#InvocationOperation
NSInvocationOperation *operation4=[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(downloadOperation) object:nil];
#添加操作到队列
[queue addOperation:operation1];
[queue addOperation:operation2];
[queue addOperation:operation3];
[queue addOperation:operation4];
[queue addOperationWithBlock:^{
NSLog(@"%@--下载第四张图片",[NSThread currentThread]);
}];
[queue addOperationWithBlock:^{
NSLog(@"%@--下载第五张图片",[NSThread currentThread]);
}];
# [queue cancelAllOperations];
}
-(void)downloadOperation{
NSLog(@"downloadOperation--%@",[NSThread currentThread]);
}
-(void)test03{
dispatch_group_t group=dispatch_group_create();
dispatch_queue_t queue=dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
#下载第一张图片
static UIImage *image1=nil;
# __block UIImage *image1=nil;
dispatch_group_async(group, queue, ^{
NSURL *url1=[NSURL URLWithString:@"http:#pic1.nipic.com/2008-12-25/2008122510134038_2.jpg"];
NSData *data1=[NSData dataWithContentsOfURL:url1];
image1=[UIImage imageWithData:data1];
NSLog(@"image1--%@",[NSThread currentThread]);
});
#下载第二张图片
static UIImage *image2=nil;
# __block UIImage *image2=nil;
dispatch_group_async(group, queue, ^{
NSURL *url2=[NSURL URLWithString:@"https:#www.baidu.com/img/bd_logo1.png"];
NSData *data2=[NSData dataWithContentsOfURL:url2];
image2=[UIImage imageWithData:data2];
NSLog(@"image2--%@",[NSThread currentThread]);
});
dispatch_group_notify(group, queue, ^{
NSLog(@"notify--%@",[NSThread currentThread]);
#开启上下文
UIGraphicsBeginImageContextWithOptions(image1.size, NO, 0.0);
#绘制第一张图片
CGFloat image1W=image1.size.width;
CGFloat image1H=image1.size.height;
[image1 drawInRect:CGRectMake(0, 0, image1W, image1H)];
#绘制第二张图片
CGFloat image2W=image2.size.width;
CGFloat image2H=image2.size.height;
[image2 drawInRect:CGRectMake(image1W-image2W, image1H-image2H, image2W, image2H)];
#获取绘制好的图片
UIImage *image=UIGraphicsGetImageFromCurrentImageContext();
#关闭上下文
UIGraphicsEndImageContext();
#回主线程刷新界面
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"async--%@",[NSThread currentThread]);
self.imageView.image=image;
});
});
}
-(void)test02{
#第一张图片
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSURL *url1=[NSURL URLWithString:@"http:#pic1.nipic.com/2008-12-25/2008122510134038_2.jpg"];
NSData *data1=[NSData dataWithContentsOfURL:url1];
self.image1=[UIImage imageWithData:data1];
[self mergerImage];
});
#第二张图片
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSURL *url2=[NSURL URLWithString:@"https:#www.baidu.com/img/bd_logo1.png"];
NSData *data2=[NSData dataWithContentsOfURL:url2];
self.image2=[UIImage imageWithData:data2];
[self mergerImage];
});
}
#合并图片
-(void)mergerImage{
if (self.image1 == nil || self.image2 == nil) {
return;
}else{
UIGraphicsBeginImageContextWithOptions(self.image1.size, NO, 0.0);
#绘制第一张图
CGFloat image1W=self.image1.size.width;
CGFloat image1H=self.image1.size.height;
[self.image1 drawInRect:CGRectMake(0, 0, image1W, image1H)];
#绘制第二张图
CGFloat image2W=self.image2.size.width;
CGFloat image2H=self.image2.size.height;
[self.image2 drawInRect:CGRectMake(image1W-image2W, image1H-image2H, image2W, image2H)];
#获取绘制后的图片
UIImage *image=UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
#UI界面显示
dispatch_async(dispatch_get_main_queue(), ^{
self.imageView.image=image;
});
}
}
-(void)test01{
dispatch_queue_t queue=dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
NSLog(@"%@--global_queue",[NSThread currentThread]);
#下载第一张图片
NSURL *url1=[NSURL URLWithString:@"http:#pic1.nipic.com/2008-12-25/2008122510134038_2.jpg"];
NSData *data1=[NSData dataWithContentsOfURL:url1];
UIImage *image1=[UIImage imageWithData:data1];
#下载第二张图片
NSURL *url2=[NSURL URLWithString:@"https:#www.baidu.com/img/bd_logo1.png"];
NSData *data2=[NSData dataWithContentsOfURL:url2];
UIImage *image2=[UIImage imageWithData:data2];
#合并图片
UIGraphicsBeginImageContextWithOptions(image1.size, NO, 0);
#绘制第一张图片
CGFloat image1W=image1.size.width;
CGFloat image1H=image1.size.height;
[image1 drawInRect:CGRectMake(0, 0, image1W, image1H)];
#绘制第二张图片
CGFloat image2W=image2.size.width*0.5;
CGFloat image2H=image2.size.height*0.5;
[image2 drawInRect:CGRectMake(image1W-image2W, image1H-image2H, image2W, image2H)];
#获取绘制好的合成图片
UIImage *image=UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"%@--main_queue",[NSThread currentThread]);
self.imageView.image=image;
});
});
}
