从函数返回值而不退出C中的函数

Question

I have a C program where via tcp socket I am sending a command to the peer process. On receiving this command, the peer process will start performing the requested command. But, it takes long time and I don't want the tcp socket to wait for long time for a return value. I think, fork a process will help me to do this. But, I want some other ways to make this thing work out. Please share your thoughts and experience related to this. Please help. thanks in advance,

Answer 1

There are many forms of Inter Process Communication (IPC) strategies in UNIX. One of my favorite is to spawn a child process and receive a notification upon its demise. A primer on IPC can be found here and an example of asynchronously waiting on a child processes death can be found here . If you don't want to spawn a separate process you can used named pipes to have information flow back and forth between the two processes.

Answer 2

You can use a thread and wait on it until the reply comes. pthread and wait will do just fine(threads are light weight processes though).

If you really want to do this by never spawning a process, you'll have to resort to something like callbacks when the TCP reply is received, this might be available from TCP wrapper libraries but including something like this or making something like it doesn't make sense if you are not waiting for a lot of replies. For a few reply waits threads are fine.

Answer 3

I don't have it clear what you mean. You say you want to give an answer before you know the result, or may be, the return value does not depend on the process itself. In term of transactional communications there two approaches, "synchronous" and "asynchronous" transactions. The former waits until the server completes de process and gives the result, the second one will send the request and gets a token, close the socket and later on it will request the result with that token. So, what you could do is give to the requested peer a token where it can ask for an answer once the process is finished. Note that you may give an answer which indicates "the process is still running, try later". In your sever code you need to program this scenario, give each process a number, keeps the result with that number and, when requested, with that number send the results. If this is not appropriate, please explain in more detail what you're trying to accomplish.