NSOperationQueue用法

    operationQueue = [[NSOperationQueue alloc] init];
    [operationQueue setMaxConcurrentOperationCount:2];
    NSInvocationOperation *op0 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(loadingnv) object:nil];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(loading) object:nil];
    [operationQueue addOperation:op];
    [operationQueue addOperation:op0];