获取签名的过程中，网络不好时，会造成主线程堵塞

[chenyingchao]

Base Info for this issue

// MARK: - Signature

• (AVIMSignature *)getSignatureByDataSourceWithAction:(NSString *)action
  conversationId:(NSString *)conversationId
  clientIds:(NSArray<NSString *> *)clientIds
  {
  AssertRunInIMClientQueue;

  NSString *clientId = _clientId;

  __block AVIMSignature *signature = nil;

  id signatureDataSource = _signatureDataSource;

  if (signatureDataSource) {

    SEL aSel = @selector(signatureWithClientId:conversationId:action:actionOnClientIds:);
    
    if ([signatureDataSource respondsToSelector:aSel]) {
        
        dispatch_sync(dispatch_get_main_queue(), ^{
            
            signature = [signatureDataSource signatureWithClientId:clientId
                                                    conversationId:conversationId
                                                            action:action
                                                 actionOnClientIds:clientIds];
        });
    }
  

  }

  return signature;
  }

在AVOSCloudIM 9.0.1中 , 获取签名的过程中，网络不好时，会造成主线程堵塞。

1. ChatKit Version：0.7.17
2. App-ID: XX
3. Language：Objective-C
4. iOS System Version：iOS10
5. Prototype（是否是真机）：YES
6. Issue Type：Crash、Bug、Enhancement（希望能支持一个新需求）、Q-A

1. How to repeat the problem.

1. 在AVOSCloudIM 9.0.1中 APP启动
   2.获取签名

2. Please help me in this way.

在9.0之前版本 是在子线程调用签名

3. Here is a Demo.

4. Here is my Debug log