and thanks for taking a look at the question.
The background
I have several machines that continuously spawn multiple (up to 300) PHP console scripts in a very short time frame. These scripts run quickly (less than a second) and then exit. All of these scripts need read only access to a large trie structure which would be very expensive to load into memory each time each one of the scripts runs. The server runs Linux.
My solution
Create a C daemon that keeps the trie structure in memory and receives requests from the PHP clients. It would receive a request from every one of the PHP clients, perform the lookup on the memory structure and respond with the answer, saving the PHP scripts from doing that work. Both requests and responses are short strings (no longer than 20 characters)
My problem
I am very new to C daemons and inter process communication. After much research, I have narrowed the choices down to Message Queues and Unix domain sockets. Message Queues seem adequate because I think (I may be wrong) that they queue up all of the requests for the daemon to answer them serially. Unix domain sockets seem to be easier to use, though. However, I have various questions I have not been able to find answers to:
- How can a PHP script send and receive messages or use a UNIX socket to communicate with the daemon? Conversely how does the C daemon keep track of which PHP process it has to send a reply to?
- Most examples of daemons I have seen use an infinite while loop with a sleep condition inside. My daemon needs to service many connections that can come at any time, and response latency is critical. How would the daemon react if the PHP script sends a request while it is sleeping? I have read about poll and epoll, would this be the correct way to wait for a received message?
- Each PHP