gistfile1.m

{
    NSOperationQueue * queue = [[[NSOperationQueue alloc] init] autorelease];
    
    NSURL * url = [NSURL URLWithString:@"http://www.example.com/"];
    id<DDFuture> futureData = [queue dd_submitCallableBlock:^id (NSError **error) {
        NSData * data = [NSData dataWithContentsOfURL:url options:0 error:error];
        return data;
    }];

    // This blocks for the result
    NSError * error = nil;
    NSData * data = [futureData result:&error];
    
    if (data != nil) {
        NSString * string = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
        NSLog(@"String:\n%@", string);
    } else {
        NSLog(@"Error: %@", error, [error userInfo]);
    }
}