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From André Warnier ...@ice-sa.com>
Subject Re: [users@httpd] global variable use in mod_proxy_http.c
Date Wed, 24 Jun 2009 21:31:43 GMT
Brian Kim wrote:
> Hi. All.
> 
> In mod_proxy_http.c, I globally declared a variable, like unsiged int count = 0;
> 
> And I make it increase whenever the proxy gets a new http request.
> 
> I expect it increases like 1, 2, 3, 4,... but it is always same 1.
> 
> Does anydoby know why this happens? How can I use a global variable in
> mod_proxy_http?
> 
Not a simple answer, but read this :
http://marc.info/?l=apache-httpd-users&m=124467015611975&w=2

The basic point is : when it starts, Apache is a single process.  That 
one loads mod_proxy, with your variable initialised to 0.
Then that main Apache forks into children.  Each child is an exact copy, 
thus also with the variable = 0.
The main Apache does not serve requests, so its copy always remains 0.
But it distributes requests, 1 per child, as they come in.
So probably your first request gets handled by child #1.  It serves the 
request, and increments the variable, which for this child is now 1.
Then your next request comes in, and is handled by child #2.
Its variable is still 0.  So it serves the request and increments the 
variable.
Then your next request comes in and is served by child #3.
And so on.
Until... enough requests have come in, that a child that has been used 
before, gets re-used.  Then the variable is at 1, and now becomes 2.
But only in that child.
And so on.

Got it ?

If you start your Apache with a maximum of 3 children e.g., then after 4 
requests you are guaranteed to see a 2.

Morality : you have to find a place to store your counter, that is 
common to all children (or threads).  And of course synchronise access 
to it.


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