Re: Any caveats to using fork in a Foundation/CoreFoundation tool?
Re: Any caveats to using fork in a Foundation/CoreFoundation tool?
- Subject: Re: Any caveats to using fork in a Foundation/CoreFoundation tool?
- From: glenn andreas <email@hidden>
- Date: Thu, 25 Oct 2007 12:15:30 -0500
On Oct 25, 2007, at 11:45 AM, Jim Correia wrote:
I have the need to launch a tool from my GUI application that needs
to be in its own process group (i.e. the parent process should not
be the GUI app which launched it, since it needs to outlive the
parent process.)
It will use CFMessagePort to communicate with the parent app.
I seem to recall that using fork not followed immediately by exec
was a bad idea for Foundation/CoreFoundation tools or applications,
but at the moment I can't find those references in the archives.
Is using fork (or daemon, as the case may be) at the top of main
going to cause me grief when I want to later use Foundation or
CoreFoundation services?
Yes, it will cause problems - basically, after a fork, you not
suppose use anything above libSystem - according to POSIX, you're not
even suppose to use anything except those that are listed as async
signal handler safe (according to one web page "In the child, do not
call any library functions after calling fork() and before calling
exec(). One of the library functions might use a lock that was held
in the parent at the time of the fork(). The child process may
execute only Async-Signal-Safe operations until one of the exec()
handlers is called"). So even malloc could be bad...
So basically all of CoreFoundation is bad (check out the source for
CFMachPort.c in the current CF source to see where it tries to
gracefully handle this problem - with graceful meaning "print a
meaningful message and exit" rather than "hang").
Any other recommended approaches?
I'd add a "magic flag" to the argv list - your tool will check that,
and if missing, will fork and exec itself with that flag added (and
then quit). If it is present, then you are good to go...
Glenn Andreas email@hidden
<http://www.gandreas.com/> wicked fun!
quadrium2 | build, mutate, evolve, animate | images, textures,
fractals, art
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