dispatch_barrier_async一些用法

最新推荐文章于 2024-09-12 15:58:01 发布

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本文介绍了AFNetworking中如何利用GCD确保HTTP头部字段的线程安全操作，包括读写请求头信息的方法，并解释了dispatch_barrier_async和dispatch_sync的作用。

- (NSDictionary *)HTTPRequestHeaders {
    NSDictionary __block *value;
    dispatch_sync(self.requestHeaderModificationQueue, ^{
        value = [NSDictionary dictionaryWithDictionary:self.mutableHTTPRequestHeaders];
    });
    return value;
}

- (void)setValue:(NSString *)value
forHTTPHeaderField:(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>

<span style="font-family: Arial, Helvetica, sans-serif;">
</span>

<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>