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I'm even curious to know why a flag like _PROTECT_FROM_CLOSE was created in the first place. :)
Sometimes two processes need to communicate via file descriptors and std* is not enough- Unix example I know of is UCSPI (ooks-pie) UNIX Client-Server Program Interface which qmail uses. In a case like that, you need to keep non-STD* filehandles from closing when you exec a new process, otherwise the child tries using FD 3 (or FDs 6 and 7, etc) and finds it is closed.

Unix has no problem with this, it uses fcntl($fh, F_SETFD, ~FD_CLOEXEC) and all is well. But those POSIX macros are not implemented in Win32-land, at least not in ActiveState's Perl. Hence my desire to try _PROTECT_FROM_CLOSE on FD 3.

I was all over the web looking for insight, tried other tricks like setting $^F=3 (never even glanced at that perlvar before) but no luck. The best I found was a terse comment that said "Can't be done. OS limitation." which gave me the courage to give up!

Thanks for looking into it, and confirming that I'm not alone.

edit:
Here is my original goal, which seems to be elusive to many on the web: have a program write to stdout, stderr, and some 3rd stream. In Unix it would be invoked like "MyProg >stdout.log 2>stderr.log 3>extra_data.log". Windows cmd.exe shell allows FD's 3-9 in redirects but it doesn't pass them to any programs it spawns, they seem to be just for dup'ing 0,1,2 on the command line.

My idea was to write a wrapper in perl that would allow communicating with a sub-program using those higher-number, user-defined file descriptors in Win32.


In reply to Re^2: Win32API::File not setting HANDLE_FLAG_PROTECT_FROM_CLOSE (sources) by Yary
in thread Win32API::File not setting HANDLE_FLAG_PROTECT_FROM_CLOSE by Yary

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