Question

I have PHP server, in which I need to update client A about some client B action, at the moment it’s done. How it is normally being accomplished ?

My current solution would be:

1. A leaves an open $.ajax(...).done(function myCallBack(){...}); call for this.
2. when A is in myCallBack(){...} it issues another $.ajax(...).done(function myCallBack(){...});. This way the communication with server stays open for receiving new info anytime
3. the PHP would have to continually check for inter-session communication file to transfer data to/from two concurrent sessions

Leaving $.ajax(...).done(function myCallBack(){...}); open (and spawning new ones all the time) is the way to do it ?

For inter-session communication – is there a way to signal events or something like that (instead of continuously monitoring some file [a waste of resources!]) ?

Answer 1

This is how I solved it:

Client A leaves an open ajax call: $.ajax(...).done(function myCallBack(){...});: on the PHP server side (session), A locks on a semaphore using sem_acquire($semaphore_A), and waits.

Client B removes semaphore $semaphore_A using sem_remove($semaphore_A), thus releasing A that returns to client JS callback myCallBack().

Of-course, it’s very simplistic, and I use shared-memory (e.g. shm_attach()) to exchange status and data between processes.

For other developers stuck with this technique:

what took me so long to debug it, is the fact the I opened a session (session_start()) and didn’t close it (session_ write_ close()) – which locked other processes and prevented any concurrency !