On Sun, Sep 09, 2001 at 09:30:50PM +0200, Arthur Bergman wrote:
>
> I would suspect that this is solved in the perlhost/perlsys code which is win32
>specific.
> There is nothiing in ithreads that does this.
Rats.
> Relevant code is iperlsys.h PerlDir_chdir.
Thanks.
> However, should threads have different cwds?
Well, if you want to use any modules that chdir() in threaded code, I
think so. Basically, in a threaded perl, unsafe chdir should be warned
about or perl should DWIM and emulate chdir per thread (as it does on
windows). The former is the halting problem, I think ;-).
> If so it should probably be solved in perl, but can it be done portable?
Don't see why not. The real oddity here is Windows which has a cwd per
volume (A:, B:, etc), and that's either ignored in win32.c or emulated
too, not sure.
> How does Apache deal with this?
By carefully repeating "Don't Do That" as they code the httpd ;-). The
cgi-bin chdir() is done after fork()ing, and most (if not all, not sure)
other chdir()s are pre-thread-startup or when coredumping.
There was an ap_ chdir() wrapper in existance for a while, but that was
removed becuase it wasn't threadsafe and not in use.
That all being said, chdir() is probably in use in various Apache
modules here and there; they'll need a bit of porting for any OS other
than Linux, I suspect, and perhaps even on Linux (don't know if the cwd
is part of the process structures that is shared or not, need to spelunk
& test, unless somebody here knows...).
> Sarathy claims that all stjmp/longjmp code is exeucted while not
> holding any mutexes, so it should be threadsafe. One can note that
> setjmp and longjmp are not non-mt safe. But they can be used to do
> unsafe things.
Or they can be used in a safe manner, such as never jumping between
threads. setjmp() and longjmp() should be safely usable. Is the only
interaction with mutexes that you need to release any acquired after the
setjmp() before calling longjmp()?
- Barrie
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