I have been investigating this problem further.
The problem appears to be if any module tries to set an environment variable during
the first init run then it will get wiped out by the shutdown of perl. This then
means that the during the second init run the environment variable will not exist and
therefore the module could possibly fail if it depended on it being in place. I have
now recreated this with a simple module of my own.
What I believe is happening .......
The "perl_startup" routine appears to use some of the perl routines to make a copy of
the environment, and points the exec process at this new environment. The
"perl_startup" routine is run before any of the init routines.
The init routines then run and a module set an environment variable. This variable is
stored in the new copied environment.
After the init processes finish Apache performs the shutdown of the modules to test
the restart process. During this phase mod_perl runs the "mp_dso_unload" routine
which will shutdown perl. My belief is during this shutdown the new environment is
dereferenced, and therefore the environment is set back to the original pointer. What
this means is all the environment variables that were set during the first run of the
init process are lost. The upshot of this is during the second init run you start
with a fresh environment.
The reason I am now fairly sure this is the case is if you set the environment
variable PERL_DESTRUCT_LEVEL to -1 it forces the "mp_dso_unload" routine NOT to unload
perl. This means the new environment is not lost, and both my test module and the IBM
module now work as expected.
I believe the problem lies somewhere in the "perl_startup" routine where it makes
changes to the environment.
Possible culprits....
....
perl_clear_env();
mod_perl_pass_env(p, cls);
...
...
/* Force the environment to be copied out of its original location
above argv[]. This fixes a crash caused when a module called putenv()
before any Perl modified the environment - environ would change to a
new value, and the check in my_setenv() to duplicate the environment
would fail, and then setting some environment value which had a previous
value would cause perl to try to free() something from the original env.
This crashed free(). */
my_setenv("MODPERL_ENV_FIXUP", "0");
my_setenv("MODPERL_ENV_FIXUP", NULL);
Clearly there has been a change in the way perl does some of the environment handling
between 5.005 and 5.8+ as both the IBM module and my test module work fine with 5.005.
My questions are now
1/ What real effect on the system am I likely to suffer having the PERL_DESTRUCT_LEVEL
set to -1 ??
2/ Does anyone have any background on the "perl_startup" routine with regard to the
environment calls, and in particular the part where a forced copy of the environment
is made for a previous crash situation ? It seems this "fix" might have a side
effect of not allowing any other module to set environment variables during the init
phase.
Rgds
Darren Heather
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