6.10 Exercise: Client-Server Revisited

Section 6.4 developed an implementation of request-reply using named pipes. The implementation was limited because multiple readers do not behave well with pipes. Write a new version of these programs in which the clients send their process IDs rather than single characters . To service each request, the server uses a FIFO whose name includes the process ID of the client. After servicing the request, the server closes the response FIFO and unlinks it. Be sure that no client can cause this version of the server to exit.

Although the clients are sending multibyte process IDs to the server, the server will not receive interleaved IDs because writes to the pipe are atomic. Since only one process is reading from each pipe, reads do not need to be atomic.

If the server is responsible for creating the pipe from the process ID that is sent to it, the client may try to open the pipe before it exists, generating an error. Have the client create the reply pipe before sending its ID to the server on the request pipe. After sending its ID, the client opens the reply pipe for reading and blocks until the server opens it for writing. After the client receives its reply, it can close and unlink the reply pipe.

Note that both the client and the server need to run in the same directory so that they can access the same pipes.