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From Alex Wulms <>
Subject Question about APR SHM
Date Sat, 31 Jul 2010 16:07:05 GMT

I have got a question about APR SHM. The comments of the function
apr_shm_baseaddr_get(const apr_shm_t *m) indicate that the resulting
address is only valid in the callers address space, since the API does
not guarantee that other attaching processes will maintain the same
address mapping.

When I look at the implementation of modules that use SHM (like mod_ssl
and mod_ldap), it seems like the address returned by the function is
re-used as-is in the worker child processes. In both modules, the above
function is invoked from the post_config handler and the resulting
memory structure is then used in the worker child processes.

So my question is: when is the note about the validity of the resulting
address applicable? Is it only applicable when a new process has
attached itself explicitly to an already existing SHM segment with the
apr_shm_attach(...) function? And can I safely ignore it when it
concerns an implicit attachment (inherited) by the child process? And is
it like that on all supported platforms and not only on Unix (I know for
a fact that it is indeed like this on Unix)?

Thanks and kind regards,


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