Global Variables
The biggest single “gotcha” for
scripts running under
Apache::Registry
is caused by global variables.
The mod_cgi environment is rather kind to the
slack programmer. Your scripts, which tend to be short and simple,
get loaded, run, and then thrown away. Perl rather considerately
initializes all variables to undef
at startup, so
one tends to forget about the dangers they represent.
Unhappily, under mod_perl and
Apache::Registry
, scripts effectively run as
subroutines. Global variables get initialized at startup as usual,
but not again, so if you don’t explicitly initialize
them at each call, they will carry forward whatever value they had
after the last call. What makes these bugs more puzzling is that as
the Apache child processes start, each one of them has its variables
set to 0. The errant behavior will not begin to show until a child
process is used a second time — and maybe not even then.
There are several lines of attack:
Do away with every global variable that isn’t absolutely necessary
Make sure that every global variable that survives is initialized
Put your code into modules as subroutines and call it from the main script — for some reason global variables in the module will be initialized
To illustrate this tiresome behavior we created a new directory /usr/www/APACHE3/APACHE3/site.mod_perl/mod_perl and copied everything across into it from.../mod_cgi. The startup file go was now:
httpd.perl -d /usr/www/APACHE3/APACHE3/site.mod_perl/mod_perl
The Config ...
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