dispatch_barrier_async一些用法

来源：互联网发布：安庆网络问政平台2017 编辑：程序博客网时间：2024/05/21 11:28

- (NSDictionary *)HTTPRequestHeaders {    NSDictionary __block *value;    dispatch_sync(self.requestHeaderModificationQueue, ^{        value = [NSDictionary dictionaryWithDictionary:self.mutableHTTPRequestHeaders];    });    return value;}- (void)setValue:(NSString *)valueforHTTPHeaderField:(NSString *)field{    dispatch_barrier_async(self.requestHeaderModificationQueue, ^{        [self.mutableHTTPRequestHeaders setValue:value forKey:field];    });}- (NSString *)valueForHTTPHeaderField:(NSString *)field {    NSString __block *value;    dispatch_sync(self.requestHeaderModificationQueue, ^{        value = [self.mutableHTTPRequestHeaders valueForKey:field];    });    return value;}

1、在AFNetworking中，dispatch_barrier_async用来保证写线程的安全性，；以上面self.mutableHTTPRequestHeader 为例，通过<span style="font-family: Arial, Helvetica, sans-serif;">dispatch_barrier_async，能保证每次写</span><span style="font-family: Arial, Helvetica, sans-serif;">self.mutableHTTPRequestHeader时，没有线程在读</span><span style="font-family: Arial, Helvetica, sans-serif;">self.mutableHTTPRequestHeader；同时，写入</span><span style="font-family: Arial, Helvetica, sans-serif;">self.mutableHTTPRequestHeader时是在子线程中写的</span>

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<span style="font-family:Arial, Helvetica, sans-serif;">2、</span><span style="font-family: Arial, Helvetica, sans-serif;">self.requestHeaderModificationQueue是一个并发队列，</span><span style="font-family: Arial, Helvetica, sans-serif;">dispatch_sync(self.requestHeaderModificationQueue, 实现多线程读取同一个变量，又能保证同步获取到数据</span>

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