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Surprised by limitation of Win32 "system(1" hack

by eyepopslikeamosquito (Bishop)
on Jun 24, 2015 at 05:26 UTC ( #1131761=perlquestion: print w/replies, xml ) Need Help??

eyepopslikeamosquito has asked for the wisdom of the Perl Monks concerning the following question:

On Windows, running this program:

use strict; use warnings; $| = 1; my $cmd = qq{$^X -le "print 'pid=', \$\$"}; for my $i (1..70) { print "$i: run $cmd ---------\n"; my $rc = system(1, $cmd); sleep(1); print "$i: done (rc=$rc).\n"; $rc < 0 and print "$i: ($!)\n"; }
surprised me by producing:

1: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=4600 1: done (rc=384). 2: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=3036 2: done (rc=4432). 3: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=7156 3: done (rc=6364). 4: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=5604 4: done (rc=4000). 5: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=5784 5: done (rc=2820). 6: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=1820 6: done (rc=6592). 7: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=6672 7: done (rc=6484). 8: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=6452 8: done (rc=4800). 9: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" -------- +- pid=3340 9: done (rc=6652). 10: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4620 10: done (rc=6524). 11: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4240 11: done (rc=224). 12: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=3200 12: done (rc=208). 13: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4120 13: done (rc=4112). 14: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=5324 14: done (rc=1312). 15: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=7032 15: done (rc=6272). 16: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4164 16: done (rc=6884). 17: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4504 17: done (rc=6404). 18: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6292 18: done (rc=6396). 19: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=748 19: done (rc=416). 20: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6804 20: done (rc=1296). 21: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6696 21: done (rc=5712). 22: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4028 22: done (rc=7148). 23: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=3220 23: done (rc=4852). 24: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6788 24: done (rc=92). 25: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6932 25: done (rc=3176). 26: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=960 26: done (rc=5332). 27: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4832 27: done (rc=6928). 28: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=1088 28: done (rc=4500). 29: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=3648 29: done (rc=6456). 30: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6756 30: done (rc=3568). 31: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=332 31: done (rc=1484). 32: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=5624 32: done (rc=5944). 33: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=3612 33: done (rc=6576). 34: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=828 34: done (rc=4408). 35: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=3116 35: done (rc=3172). 36: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4944 36: done (rc=5956). 37: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4752 37: done (rc=3592). 38: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6668 38: done (rc=2780). 39: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6612 39: done (rc=4128). 40: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=2500 40: done (rc=6760). 41: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6808 41: done (rc=4616). 42: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=5252 42: done (rc=2640). 43: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4396 43: done (rc=6368). 44: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=5088 44: done (rc=2604). 45: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6828 45: done (rc=6664). 46: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6012 46: done (rc=6680). 47: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6136 47: done (rc=2980). 48: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6676 48: done (rc=6556). 49: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=5764 49: done (rc=1412). 50: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6720 50: done (rc=3468). 51: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6908 51: done (rc=6156). 52: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=228 52: done (rc=2332). 53: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=5204 53: done (rc=4728). 54: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6236 54: done (rc=5952). 55: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6128 55: done (rc=6924). 56: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=5988 56: done (rc=3900). 57: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6656 57: done (rc=6604). 58: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6432 58: done (rc=32). 59: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=432 59: done (rc=6324). 60: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=2376 60: done (rc=7056). 61: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6384 61: done (rc=3432). 62: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=7152 62: done (rc=5652). 63: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=6764 63: done (rc=6480). 64: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- pid=4336 64: done (rc=5028). 65: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- 65: done (rc=-1). 65: (Resource temporarily unavailable) 66: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- 66: done (rc=-1). 66: (Resource temporarily unavailable) 67: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- 67: done (rc=-1). 67: (Resource temporarily unavailable) 68: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- 68: done (rc=-1). 68: (Resource temporarily unavailable) 69: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- 69: done (rc=-1). 69: (Resource temporarily unavailable) 70: run C:\Strawberry\perl\bin\perl.exe -le "print 'pid=', $$" ------- +-- 70: done (rc=-1). 70: (Resource temporarily unavailable)

That is, there appears to be a limit of 64 processes with the Win32 system(1 hack. Anyone know why? This is just a guess, but I remember that Win32 WaitForMultipleObjects has a limit of 64 handles.

Super search found Getting a return code from waitpid in Windows. I was using the "system(1" hack only out of laziness. I should be able to work around this limitation ... though if I need to go to the bother of calling waitpid etc. I will probably just bite the bullet and use Win32::Process instead.

Replies are listed 'Best First'.
Re: Surprised by limitation of Win32 "system(1" hack
by BrowserUk (Patriarch) on Jun 24, 2015 at 12:24 UTC
    though if I need to go to the bother of calling waitpid etc. I will probably just bite the bullet and use Win32::Process instead.

    Why? Why is "the bother of calling waitpid" so onerous?

    This just ran to completion in 10 seconds or so(Note:1000):

    use strict; use warnings; $| = 1; my $cmd = qq{$^X -le "print 'pid=', \$\$"}; for my $i ( 1 .. 1000 ) { print "$i: run $cmd ---------\n"; my $rc = system( 1, $cmd ); waitpid( $rc, 0 ); }

    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
    I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!
Re: Surprised by limitation of Win32 "system(1" hack
by Anonymous Monk on Jun 24, 2015 at 07:11 UTC
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