Indy10 TCP client deliver reply to sending procedure

Question

I am making a client program in Delphi 7 with Indy 10.

It must connect to the server with TIdTCPClient and keep alive the connection for sending and getting commands and replies until the program is closed.

The server can maintain only one constant connection per client to send info-messages. TIdTCPClient is listening through a reading thread.

QUESTION:
I am sending a request to the server (using WriteLn) from some procedure to get a list of strings, for example. How can I get the answer (reply) for that request in the same procedure, without leaving it? Like using TIdHTTP.

I see 2 solutions:

1. making the request from one procedure and handle it in other - the code and logic will be more complicated.

2. for each request in a procedure, create a new TIdTCPClient (Connect, WriteLn, ReadLn, Disconnect, Free) and handle request. But I do not like this solution as it causes large overhead.

Answer 1

Since a reading thread is involved, it does complicate things a little. The reading thread needs to be the one to receive all of the replies and then it can dispatch them to handlers as needed.

Your first solution is fine, if you don't mind breaking up your code. This is the simplest solution, and the best one if the main thread is the one making the requests. You should never block the main thread.

As you mentioned, your second solution is not a very good one.

Another solution would be to create a TEvent for each request, and put each request into a list/queue somewhere. Have the reading thread find and signal the appropriate event when a response is received. The sending procedure can then wait on the event until it is signaled ( TThread.Synchronize() works this way, for example). If the procedure is running in the main thread, use MsgWaitForMultipleObjects() to do the wait, so you can still service the main message queue while waiting.