NSInvocationOperation ignoring maxConcurrentOperationCount

Question

我正在尝试使用NSInvocationOperation排队一些TWRequest调用。它似乎以正确的顺序添加方法调用，但doSomething:方法在同一时间被调用，即并发运行，而不是一个接一个，这就是我想要实现的。

此外，complete的顺序错误，这表明它不是一个接一个地运行…

- (void)prepare {
    if(!self.queue){
        self.queue = [[NSOperationQueue alloc] init];
        [self.queue setMaxConcurrentOperationCount:1];
    }
    for(NSString *text in calls){
        NSLog(@"Adding to Queue... %@", text);
        NSInvocationOperation *indexOperation = [[NSInvocationOperation alloc] initWithTarget:self  
                                                                                     selector:@selector(doSomething:) object:text];
        [self.queue addOperation:indexOperation];
    }     
}
- (void)doSomething:(NSString*)someText {
    TWRequest *request = [[TWRequest alloc] initWithURL:[NSURL URLWithString:@"http://something.com"] parameters:nil requestMethod:TWRequestMethodGET];
    NSLog(@"About to Perform Request... %@", someText);
    [request performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error)
     {
         dispatch_sync(dispatch_get_main_queue(), ^{
              // works fine
              NSLog(@"Network Finished... %@", someText);
         });
     }];
}

在日志中我看到这样:

2011-12-30 18:34:34.553 app[32745:10703] Adding to Queue... 1
2011-12-30 18:34:34.555 app[32745:10703] Adding to Queue... 2
2011-12-30 18:34:34.556 app[32745:10703] Adding to Queue... 3
2011-12-30 18:34:34.557 app[32745:13e03] About to Perform Request... 1
2011-12-30 18:34:34.560 app[32745:13e03] About to Perform Request... 2
2011-12-30 18:34:34.563 app[32745:13e03] About to Perform Request... 3
2011-12-30 18:34:35.303 app[32745:10703] Network finished... 3
2011-12-30 18:34:35.454 app[32745:10703] Network finished... 2
2011-12-30 18:34:35.601 app[32745:10703] Network finished... 1

我希望看到(2)在(1)完成后执行请求…指针吗?

Answer 1

操作队列工作正常。正如@Joe在评论中所说，performRequestWithHandler:启动异步连接并立即返回。您可以通过在doSomething的末尾添加NSLog来看到这一点，如下所示:

- (void)doSomething:(NSString*)someText {
    TWRequest *request = [[TWRequest alloc] initWithURL:[NSURL URLWithString:@"http://something.com"] parameters:nil requestMethod:TWRequestMethodGET];
    NSLog(@"About to Perform Request... %@", someText);
    [request performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error)
     {
         dispatch_sync(dispatch_get_main_queue(), ^{
              // works fine
              NSLog(@"Network Finished... %@", someText);
         });
     }];
    NSLog(@"doSomething Finished");
}

要使每个请求连续发生，您需要在操作中使请求同步(使用signedRequest方法和同步NSURLConnection)，或者不使用操作队列并在当前请求的完成处理程序中调用下一个请求。请记住，如果使用操作队列，则执行操作的顺序不是基于它们添加的顺序。您可以考虑将GCD直接用于串行调度队列。