Question

我想等待几个异步任务完成并尝试使用dispatch_group实现它，请参阅apple docs：Concurrency Programming Guide。

但是当我进入调度组时，sendAsynchronousRequest只是没有返回响应。日志不显示任何错误。谁能告诉我我做错了什么？

dispatch_group_t group = dispatch_group_create();

dispatch_group_enter(group);
// get Data from Server
NSString *url = [ConfigurationManager getDomain];
url = [url stringByAppendingString:[NSString stringWithUTF8String:URL_GET_JACKPOT]];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setTimeoutInterval:TIMEOUT_INTERVAL];
[request setURL:[NSURL URLWithString:url]];

// not getting response
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue currentQueue] completionHandler:^(NSURLResponse *responseCode, NSData *responseData, NSError *error) {
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)responseCode;
    if([httpResponse statusCode] != 200){
        NSLog(@"@Error: Error getting %@, HTTP status code %li, Error: %@", url, (long)[httpResponse statusCode], error);

    }else{
        // process result

    }
    dispatch_group_leave(group); // this never gets called -> deadlock
}];
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

Answer 1

我认为class MyWidget(QtGui.QPushButton): def __init__(self, parent= None): super(MyWidget,self).__init__(parent)的响应在主线程上执行，我不在（dispatch_enter的原因）。当我创建自己的sendAsynchronousRequest对象时，它可以工作。

NSOperationQueue

Answer 2

是的，正如你所说，尝试使用不同的队列，否则你将陷入僵局。

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    dispatch_group_t group = dispatch_group_create();

    dispatch_group_enter(group);
    // get Data from Server
    NSString *url = [ConfigurationManager getDomain];
    url = [url stringByAppendingString:[NSString stringWithUTF8String:URL_GET_JACKPOT]];
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setTimeoutInterval:TIMEOUT_INTERVAL];
    [request setURL:[NSURL URLWithString:url]];

    // not getting response
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *responseCode, NSData *responseData, NSError *error) {
        NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)responseCode;
        if([httpResponse statusCode] != 200){
            NSLog(@"@Error: Error getting %@, HTTP status code %li, Error: %@", url, (long)[httpResponse statusCode], error);

        }else{
            // process result

        }
        dispatch_group_leave(group); // this never gets called -> deadlock
    }];
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
});

在dispatch_group_enter之后没有调用sendAsynchronousRequest

2 个答案: