Getting your own process ID

From: Joshua Beall (jbeall_at_donotspam.remove.me.heraldic.us)
Date: 03/25/05

  • Next message: Andy Hassall: "Re: Image function puzzle" 
    Date: Thu, 24 Mar 2005 23:31:12 GMT

    Hi All,

    I am doing some work where I want to do locking, and prevent scripts from
    running in parallel. I see that I could use the semaphore mechanism, but
    I'd like for my code to be portable, and that extension is not enabled in
    many places.

    I need some way for a process to uniquely identify itself. It can then look
    at the storage container (flat file, DB, whatever is appropriate in
    context), check to see if the requested semaphore is available, and if it
    is, acquire it and then mark itself as the owner. It can then check that it
    did in fact get ownership (as opposed to another process which attempted to
    acquire it at the exact same moment) before proceeding.

    However I am stumped at the point where it needs to indicate ownership. How
    does the PHP script identify itself? It can't use the script name,
    obviously - lots of instances of the script may be running. It can't use
    session ID - the user might submit duplicate requests, and they would both
    have the same session ID. The best I have been able to think of is to use
    the sha1(microtime()) to generate a unique key. But this isn't quite
    foolproof, as it is theoretically possible, though unlikely, for two
    requests to be at the exact same instant.

    The answer that comes to my mind would be to use the process ID. This is
    necessarily unique across the entire server, correct? It seems to be
    exactly what I need. But I can't seem to figure out how to determine the
    current process ID from within PHP. Is this even possible?

    Any ideas?

      -Josh

    p.s. Please forgive me if I have misused the term "semaphore" - I know it
    only from the context I have heard it used in, I don't know the textbook
    definition.

  • Next message: Andy Hassall: "Re: Image function puzzle"

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