Berger, Daniel
2006-Nov-01 19:49 UTC
[Win32utils-devel] fatal flaw in popen4 on windows? [WAS] Re: Nonblocking IO read (fwd)
Hi Ara, I''ll take a look. In the meantime, I''ve cc''d the win32utils-devel mailing list to see if anyone has any ideas/suggestions. Regards, Dan> -----Original Message----- > From: ara.t.howard at noaa.gov [mailto:ara.t.howard at noaa.gov] > Sent: Wednesday, November 01, 2006 12:36 PM > To: Berger, Daniel > Subject: fatal flaw in popen4 on windows? [WAS] Re: > Nonblocking IO read (fwd) > > > > hi dan- > > forgot to cc you on this... hopefully you''ll have some suggestions? > > regards. > > -a > -- > my religion is very simple. my religion is kindness. -- the > dalai lama > > ---------- Forwarded message ---------- > Date: Wed, 1 Nov 2006 12:19:12 -0700 (MST) > From: ara.t.howard at noaa.gov > To: ruby-talk ML <ruby-talk at ruby-lang.org> > Subject: fatal flaw in popen4 on windows? [WAS] Re: > Nonblocking IO read > > > On Thu, 2 Nov 2006, Robert Klemme wrote: > > > Tom Pollard wrote: > >> Anyway, you would only need nonblocking IO if you wanted > to read bits > >> of the > >> stderr stream before the command exited, but that doesn''t > sound like what > >> you''re want. > > > > Actually this is not correct: if there is a lot written to > stderr then > > you need to read that concurrently. If you do not do that then the > > process will block on some stderr write operation that fills up the > > pipe and you get a deadlock because your code waits for process > > termination. > > not only is that true but, afaik, it''s why popen4 cannot even > work on windows! this program will eventually hang on either > windows or unix > > > harp:~ > cat a.rb > require ''rubygems'' > require ''popen4'' > > n = (ARGV.shift || 4242).to_i > ruby = ARGV.shift || ''ruby'' > > system "ruby -e 42" or abort "ruby not in your path!" > > STDOUT.sync = STDERR.sync = true > > program = <<-program > #{ n }.times do > t = Time.now.to_f > STDOUT.puts t > STDERR.puts t > end > program > > > POpen4.popen4(ruby) do |stdout, stderr, stdin, pid| > STDOUT.puts pid > > stdin.puts program > stdin.close > > Thread.new{ stdout.each{|line| STDOUT.puts line} } > # > # uncomment and it won''t hang!!! > # > #Thread.new{ stderr.each{|line| STDERR.puts line} } > end > > puts ''done'' > > > > however, on windows it will always hang - even if the line > above is uncommented. this is because if one popen4s a > process it''s __essential__, as robert correctly points out, > to continually consume any stdout or stderr produced - > otherwise the program will eventually get stuck in EPIPE and > you''ll be waiting for this stuck program. > > and here''s the rub: you cannot reliably consume both stdout > and stderr under windows using threads or, afaik, nonblocking > io. perhaps the new nonblock_* methods could help with this? > it''d no doubt be a major reworking... > > *** i''m really hoping someone will chime in here and prove me > wrong *** > > for reference i''m including the code for my open4 lib''s spawn > method: which illustrates the logical concept of what must be > done to avoid a subprocess blocked writing to it''s parent''s pipes... > > > # > # for complete code see > # http://codeforpeople.com/lib/ruby/open4/open4-0.9.1/lib/open4.rb > # http://rubyforge.org/frs/?group_id=1024&release_id=7556 > # > > def spawn arg, *argv #--{{{ > argv.unshift(arg) > opts = ((argv.size > 1 and Hash === argv.last) ? argv.pop : {}) > argv.flatten! > cmd = argv.join('' '') > > getopt = getopts opts > > ignore_exit_failure = getopt[ ''ignore_exit_failure'', > getopt[''quiet'', false] > ] > ignore_exec_failure = getopt[ ''ignore_exec_failure'', > !getopt[''raise'', true] > ] > exitstatus = getopt[ %w( exitstatus exit_status status ) ] > stdin = getopt[ %w( stdin in i 0 ) << 0 ] > stdout = getopt[ %w( stdout out o 1 ) << 1 ] > stderr = getopt[ %w( stderr err e 2 ) << 2 ] > pid = getopt[ ''pid'' ] > timeout = getopt[ %w( timeout spawn_timeout ) ] > stdin_timeout = getopt[ %w( stdin_timeout ) ] > stdout_timeout = getopt[ %w( stdout_timeout io_timeout ) ] > stderr_timeout = getopt[ %w( stderr_timeout ) ] > status = getopt[ %w( status ) ] > cwd = getopt[ %w( cwd dir ), Dir.pwd ] > > exitstatus > case exitstatus > when TrueClass, FalseClass > ignore_exit_failure = true if exitstatus > [0] > else > [*(exitstatus || 0)].map{|i| Integer i} > end > > stdin ||= '''' if stdin_timeout > stdout ||= '''' if stdout_timeout > stderr ||= '''' if stderr_timeout > > started = false > > status > begin > Dir.chdir(cwd) do > Timeout::timeout(timeout) do > popen4(*argv) do |c, i, o, e| > started = true > > %w( replace pid= << push update ).each do |msg| > break(pid.send(msg, c)) if pid.respond_to? msg > end > > # > # this is the critical bit!!! > # > > te = ThreadEnsemble.new c > > te.add_thread(i, stdin) do |i, stdin| > relay stdin, i, stdin_timeout > i.close rescue nil > end > > te.add_thread(o, stdout) do |o, stdout| > relay o, stdout, stdout_timeout > end > > te.add_thread(e, stderr) do |o, stderr| > relay e, stderr, stderr_timeout > end > > te.run > end > end > end > rescue > raise unless(not started and ignore_exec_failure) > end > > raise SpawnError.new(cmd, status) unless > (ignore_exit_failure or (status.nil? and > ignore_exec_failure) or > exitstatus.include?(status.exitstatus)) > > status > #--}}} > end > > > kind regards. > > -a > -- > my religion is very simple. my religion is kindness. -- the > dalai lama > > -a > -- > my religion is very simple. my religion is kindness. -- the > dalai lama >This communication is the property of Qwest and may contain confidential or privileged information. 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