Re: [sr-dev] Thread safety of global variables used in app_perl

Hi Torrey,

I don't think that's how the app_perl module works. I believe it spawns a single instance of the interpreter that is shared among the processes. I could be mistaken, but that's how it looks from the module code.

On 10/14/2016 03:22 AM, Torrey Searle wrote:

My experience with app_perl is that global variables are not shared between processes. So if you have 10 kamailio processes you would have 10 different %hash with different values. So it is thread safe, but perhaps isn't what you want.

Torrey

On 13 October 2016 at 23:15, Alex Balashov <abalashov@evaristesys.com mailto:abalashov@evaristesys.com> wrote:

I meant a global Perl variable -- one that would persist in a
persistent interpreter. Specifically, a "package variable" of this type:

   our %hash = ();


On 10/13/2016 04:26 PM, Daniel-Constantin Mierla wrote:

    Hello,

    is it about a global variable defined inside the perl script or
    you mean
    kamailio.cfg variables? The terminology you used might be clear
    for Perl
    guys, but as I am not one, I want to clarify it...

    As generic remarks -- kamailio is multi-process application, so each
    child is a process, not a thread. Each process has its own private
    memory space, so a global kamailio.cfg variable such as $var(x) is
    defined in each process and each process has access to the one
    specific
    to it. There are shared memory variables, like $shv(z) that all
    processes can access and change, requiring synchronization to
    avoid races.

    Cheers,
    Daniel


    On 13/10/16 19:13, Alex Balashov wrote:

        Hi,

        Given the presence of a global (e.g. "our") package variable
        in an
        embedded Perl script used through app_perl, is there any
        implicit
        thread safety?

        That is to say, can a Perl function invoked by one SIP
        worker reset
        the value of a global while another instance of the function
        invoked
        by a different SIP worker is accessing it?

        And if so, is it safe to use generic perlthr locking to
        avoid this?

        Thanks!

        -- Alex




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Alex Balashov | Principal | Evariste Systems LLC

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