in reply to Re: Threaded MPM Sharing Variables (this time with complete test code)
in thread Threaded MPM Sharing Variables (this time with complete test code)

After a few more attempts at leaning on F5, I am indeed getting multiple "Initializing"-lines in the logfile.
Then this occurred to me:
root@myserver:/usr/local/lib/site_perl/U2D# ps aux | grep apa
root      9546  0.0  0.3 148856  9920 ?        Ss   13:16   0:00 /usr/
+sbin/apache2 -k start
www-data  9549  0.0  0.3 173424  9880 ?        S    13:16   0:00 /usr/
+sbin/apache2 -k start
www-data  9550  0.0  0.3 173424  9860 ?        S    13:16   0:00 /usr/
+sbin/apache2 -k start
www-data  9551  0.0  0.3 173424  9860 ?        S    13:16   0:00 /usr/
+sbin/apache2 -k start
www-data  9552  0.0  0.3 173424  9860 ?        S    13:16   0:00 /usr/
+sbin/apache2 -k start
www-data  9553  0.0  0.3 173424  9860 ?        S    13:16   0:00 /usr/
+sbin/apache2 -k start
www-data  9618  0.0  0.3 173424  9860 ?        S    13:19   0:00 /usr/
+sbin/apache2 -k start
root      9723  0.0  0.0   7624   920 pts/0    S+   13:20   0:00 grep 
+apa
root@myserver:/usr/local/lib/site_perl/U2D# grep Initializing /var/www
+/testSharing.log
02-08-2011 13:19:38:736 9549-172922688: Initializing fruits.
02-08-2011 13:19:39:361 9550-172922688: Initializing fruits.
02-08-2011 13:19:39:426 9551-172922688: Initializing fruits.
02-08-2011 13:19:39:457 9552-172922688: Initializing fruits.
02-08-2011 13:19:39:480 9553-172922688: Initializing fruits.
02-08-2011 13:19:39:499 9618-172922688: Initializing fruits.

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Which leads me to think that for each running instance of apache2, the variable will have to be initialized at least once. Or is that too shortsighted?
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Re^3: Threaded MPM Sharing Variables (this time with complete test code)
by busymeister (Initiate) on Aug 05, 2011 at 04:55 UTC

    Hello Neighbour,

    Here is the javascript code:

    function init() {
    var options = {
        type:         "POST",
        url:        "testSharing",
    };
    for(var i = 0; i < 100; i++) $.ajax(options);
}
$(document).ready(init);

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    You need to download jQuery so that this code works but you can also create equivalent code that does not use jQuery and that does the same thing. At least you have the idea of what I am doing.

    As far as permissions go:

    sudo chown www-data:www-data /testSharing.log
sudo chmod 660 /testSharing.log

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    will do the trick.

    In your case, you are running multiple processes, as you can see in your log output (the four digit number before the hyphen after the milliseconds field). In order to force Apache to run as a single process with multiple threads, you need to change the config in apache2.conf by adding/changing:

    <IfModule mpm_worker_module>
    StartServers          1 
    MinSpareThreads       5      
    ThreadsPerChild      20 
    MaxRequestsPerChild   0
    ServerLimit           1
    PerlInterpMax         1
</IfModule>

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    Also, install the worker mpm by running:

    sudo apt-get install apache2-mpm-worker

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    Then, you will only have a single process and multiple threads, as you will clearly see when you run the javascript above and check the log file.

    I hope someone can help me with this problem. Still not clear why multiple instances are initialized.

    Sincerely,

    Pawel

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      Thanks for the javascript-code. I've got the libjs-jquery package installed, but I'm not sure how to use the javascript-code you provided (I'm not a webdev :)). Do I just put it in a .js-file and plop it in /var/www to access it using a browser? (Which only shows the contents, it doesn't run it).

      Switching from apache2-mpm-prefork (needed for php5) to apache2-mpm-worker seems to have reduced the number of running apache2-process to 3 (One owned by root, 2 by www-data).

      Putting files in / is against the filesystem-hierarchy standard (and my personal opinion on where to put files). Though your trick will allow apache2 access to /testSharing.log, this is not the place to put that file. Regardless, I got it to work using /var/www/testSharing.log (as I explained earlier), so that's not really an issue.

      Trying my previous method by holding down F5 for a bit now gets me only one occurrence of 'Initializing'.

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      Hello Neighbour,

      For some reason I cannot reply directly to your last message. Here is the html that would run my code:

      <html>
<head>
<script type="text/javascript" src="http://localhost/jquery-1.6.1.min.
+js"></script>
<script>
function init() {
    var options = {
        type:         "POST",
        url:        "http://localhost/testSharing",
    };
    for(var i = 0; i < 100; i++) $.ajax(options);
}
$(document).ready(init);
</script>
</head>
<body>
</body>
</html>

      [download]

      This is assuming that you place your jquery source at the root (the file is named jquery-1.6.1.min.js). You can download jquery from http://jquery.com/. I am not sure what the package is that you installed. Javascript files are simple text files with code that you can place directly in your document root.

      Also don't forget to update your apache2.conf file with the <IfModule mpm_worker_module> etc. This will force Apache to process requests in a single process, which you should see when you look at the log file outputted by the handler. There should only be one number in the process ID field.

      Pressing F5 with your finger is simply not fast enough, which is why we need the javascript code to pound the server with several requests simultaneously so that we force it to use at least two threads at the same time. That's why you also need to pay attention to the output in the log file I created. The process ID should be the same (threads::shared cannot share a variable across processes; testing it across multiple process does not make sense). Then, you should see different thread IDs as well. Ideally, there is only one Initializing statement even if several threads access the shared variable. My problem is that I get multiple Initializing statements even when all requests are processed in one process and multiple threads answer. Note that during my testing I had cases where some new threads did not output Initializing... but others did. So it looked to me like the sharing of the variable worked sometimes and other times it did not. I would like to understand why.

      Anyway, I am excited to hear whether you can reproduce my results as well. Don't forget to update apache2.conf and let me know how the javascript works for you.

      Sincerely,

      Pawel

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      Remove "http://localhost/" from the URLs in the html code I sent you :).
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      An even better solution is to add

      sleep(1);

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      before the line

      logTestMessage('Releasing lock.');

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      Then you can press F5 as much as you want (at least five times).
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