等待block完成再执行下一句代码

我使用afnetworking发送一个post请求, 需要得到请求结果再执行下一步代码,现在我用过如下两种方式, 但都会造成程序卡住无法往下进行.但是我在另一个put请求用了相同的方法却可行, 哪位大神有了解过这种问题的?求解释

第一种: dispatch_semaphore_t

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.requestSerializer = [AFJSONRequestSerializer serializer];
__block dispatch_semaphore_t sem = dispatch_semaphore_create(0);
[manager POST:@"http://172.16.100.85:8080/service/user/register" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
    self.requestResult = ProtocolErrorSuccess;
    if ([responseObject isKindOfClass:[NSDictionary class]]) {
        self.responseData = responseObject;
    }
    dispatch_semaphore_signal(sem);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    self.requestResult = ProtocolErrorFailure;

    dispatch_semaphore_signal(sem);
}];
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);

if(self.requestResult == ProtocolErrorSuccess) {
    [self saveToken:self.responseData];
}

第二种: NSCondition

[manager POST:@"http://172.16.100.85:8080/service/user/register" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
    self.requestResult = ProtocolErrorSuccess;
    if ([responseObject isKindOfClass:[NSDictionary class]]) {
        self.responseData = responseObject;
    }

    [condition lock];
    [condition signal];
    [condition unlock];

} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    self.requestResult = ProtocolErrorFailure;

    [condition lock];
    [condition signal];
    [condition unlock];
}];

[condition lock];
[condition wait];
[condition unlock];


if(self.requestResult == ProtocolErrorSuccess) {
    [self saveToken:self.responseData];
}