多线程篇

作者: 清风徐来121 | 来源:发表于2020-10-28 09:30 被阅读0次

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因为performSelector方法是需要依赖线程runLoop，但是开辟的子线程默认是没有开启runLoop的，所以方法调用不生效
PerformSelector详细总结

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#import "UserCenter.h"

@interface UserCenter()
{
    // 定义一个并发队列
    dispatch_queue_t concurrent_queue;
    
    // 用户数据中心, 可能多个线程需要数据访问
    NSMutableDictionary *userCenterDic;
}

@end

// 多读单写模型
@implementation UserCenter

- (id)init
{
    self = [super init];
    if (self) {
        // 通过宏定义 DISPATCH_QUEUE_CONCURRENT 创建一个并发队列
        concurrent_queue = dispatch_queue_create("read_write_queue", DISPATCH_QUEUE_CONCURRENT);
        // 创建数据容器
        userCenterDic = [NSMutableDictionary dictionary];
    }
    
    return self;
}

- (id)objectForKey:(NSString *)key
{
    __block id obj;
    // 同步读取指定数据
    dispatch_sync(concurrent_queue, ^{
        obj = [userCenterDic objectForKey:key];
    });
    
    return obj;
}

- (void)setObject:(id)obj forKey:(NSString *)key
{
    // 异步栅栏调用设置数据
    dispatch_barrier_async(concurrent_queue, ^{
        [userCenterDic setObject:obj forKey:key];
    });
}

@end

dispatch_group_async的使用

#import "GroupObject.h"

@interface GroupObject()
{
    dispatch_queue_t concurrent_queue;
    NSMutableArray <NSURL *> *arrayURLs;
}

@end

@implementation GroupObject

- (id)init
{
    self = [super init];
    if (self) {
        // 创建并发队列
        concurrent_queue = dispatch_queue_create("concurrent_queue", DISPATCH_QUEUE_CONCURRENT);
        arrayURLs = [NSMutableArray array];
    }

    return self;
}

- (void)handle
{
    // 创建一个group
    dispatch_group_t group = dispatch_group_create();
    
    // for循环遍历各个元素执行操作
    for (NSURL *url in arrayURLs) {
        
        // 异步组分派到并发队列当中
        dispatch_group_async(group, concurrent_queue, ^{
            
            //根据url去下载图片
            
            NSLog(@"url is %@", url);
        });
    }
    
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        // 当添加到组中的所有任务执行完成之后会调用该Block
        NSLog(@"所有图片已全部下载完成");
    });
}

@end