Hi,
I am experiencing a very strange problem in my Rails app. I use popen3
to execute an external program. Everything works fine in Mongrel, but
when I use the app with LSAPI, after popen3 all MySQL queries fail with
"Mysql::Error (MySQL server has gone away)". Once I comment out popen3
it works fine again.
Does anyone have the slightest idea about what goes wrong here?
Thanks
Andreas
--
Posted via http://www.ruby-forum.com/.
The problem is easy to reproduce in any Rails app using LSAPI and MySQL.
Add the following to a controller action:
require 'open3'
Open3.popen3('/usr/bin/ls') {|stdout, stdin, stderr| stdin.read }
The stdin.read is important.
--
Posted via http://www.ruby-forum.com/.
guessing, but popen3 uses fork. forking with and open db handle is undefined
for almost any db lib - of course people ignore this. i did, and had all
sorts of issues. you can read about them here
Linux Clustering with Ruby Queue: Small Is Beautiful | Linux Journal
i bet what happens is that the parent (rails) has setup an at_exit handler to
close the db on exit. when popen forks and does it's thing in the child, the
child's death kills the db handle (at_exit handlers being inherited - of
course).
this shows what i'm talking about
harp:~ > cat a.rb
at_exit{ puts 'close connection __A__' }
fork{ }
Process.wait
class Object
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
end
module Kernel
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
end
at_exit{ puts 'close connection __B__' }
fork{ }
Process.wait
harp:~ > ruby a.rb
close connection __A__
i'd try putting this
class Object
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
end
module Kernel
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
end
in environment.rb or something. another idea, i'm grasping, is some sort of
buffer flushing thing.
you could try
4242.times do |fd|
begin
IO.for_fd(fd).flush
rescue Errno::EBADF
end
end
right before the popen. wild ass guess though.
good luck.
-a
On Mon, 5 Mar 2007, Andreas Schwarz wrote:
Hi,
I am experiencing a very strange problem in my Rails app. I use popen3
to execute an external program. Everything works fine in Mongrel, but
when I use the app with LSAPI, after popen3 all MySQL queries fail with
"Mysql::Error (MySQL server has gone away)". Once I comment out popen3
it works fine again.Does anyone have the slightest idea about what goes wrong here?
--
be kind whenever possible... it is always possible.
- the dalai lama
I am experiencing a very strange problem in my Rails app. I use popen3
to execute an external program. Everything works fine in Mongrel, but
when I use the app with LSAPI, after popen3 all MySQL queries fail with
"Mysql::Error (MySQL server has gone away)". Once I comment out popen3
it works fine again.Does anyone have the slightest idea about what goes wrong here?
guessing, but popen3 uses fork. forking with and open db handle is undefined
for almost any db lib - of course people ignore this. i did, and had all
sorts of issues. you can read about them here
OK, good to know. I can close the MySQL connection for the popen3 call
and reopen it after it to avoid problems.
i bet what happens is that the parent (rails) has setup an at_exit handler to
close the db on exit.
That makes sense, although I couldn't find any reference to at_exit in
Rails or ruby-lsapi.
i'd try putting this
class Object
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
end
module Kernel
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
endin environment.rb or something.
This fixes the MySQL problem (as does manually
disconnecting/reconnecting), but now I have another problem: popen3 just
doesn't do anything when used within LSAPI. The program is never
executed. Any ideas?
Who would have thought that simply calling an external program could be
so difficult...
Thanks
Andreas
--
Posted via http://www.ruby-forum.com/\.
and reopen it after it to avoid problems.
i bet what happens is that the parent (rails) has setup an at_exit handler to
close the db on exit.That makes sense, although I couldn't find any reference to at_exit in
Rails or ruby-lsapi.
huh - maybe it's the actuall c mysql driver.
i'd try putting this
class Object
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
end
module Kernel
alias_method '__fork__', 'fork'
def fork *a, &b
at_exit{ exit! }
__fork__ *a, &b
end
endin environment.rb or something.
This fixes the MySQL problem (as does manually
disconnecting/reconnecting), but now I have another problem: popen3 just
doesn't do anything when used within LSAPI. The program is never
executed. Any ideas?
hmmm. no. must be related though. i'm staring to thinks it's lsapi which has
setup all the funky at_exit handlers, and that this is causing you grief...
Who would have thought that simply calling an external program could be
so difficult...
me 
ultimately, in ruby queue, i had to setup a drb process before setting up db
connections. then i used that drb process to do all forking/waiting for me.
here's another idea, try systemu, it does not use fork at all
gem install systemu
http://rubyforge.org/frs/?group_id=1024&release_id=7721
http://codeforpeople.com/lib/ruby/systemu/systemu-1.0.0/README
unless you need realtime control over stdin/stdout/stderr it'll do the trick.
regards.
-a
On Mon, 5 Mar 2007, Andreas Schwarz wrote:
--
be kind whenever possible... it is always possible.
- the dalai lama
Ara wrote:
def fork *a, &b
executed. Any ideas?
hmmm. no. must be related though. i'm staring to thinks it's lsapi
which has
setup all the funky at_exit handlers, and that this is causing you
grief...
I grepped for at_exit in the LSAPI source code, but didn't find
anything. Maybe it's the stdout/stderr/stdin redirection stuff...
Who would have thought that simply calling an external program could be
so difficult...me
ultimately, in ruby queue, i had to setup a drb process before setting
up db
connections. then i used that drb process to do all forking/waiting for
me.here's another idea, try systemu, it does not use fork at all
gem install systemu
http://rubyforge.org/frs/?group_id=1024&release_id=7721
http://codeforpeople.com/lib/ruby/systemu/systemu-1.0.0/README
It seems to use popen, isn't this based on fork, too?
The reason I want to use popen3 is not that I need stdin/stderr, but
that there is a clean way to pass arguments without having to build a
command line (potential escaping problems etc.).
Hi~
Ara wrote:
def fork *a, &b
executed. Any ideas?
hmmm. no. must be related though. i'm staring to thinks it's lsapi
which has
setup all the funky at_exit handlers, and that this is causing you
grief...I grepped for at_exit in the LSAPI source code, but didn't find
anything. Maybe it's the stdout/stderr/stdin redirection stuff...Who would have thought that simply calling an external program could be
so difficult...me
ultimately, in ruby queue, i had to setup a drb process before setting
up db
connections. then i used that drb process to do all forking/waiting for
me.here's another idea, try systemu, it does not use fork at all
gem install systemu
http://rubyforge.org/frs/?group_id=1024&release_id=7721
http://codeforpeople.com/lib/ruby/systemu/systemu-1.0.0/READMEIt seems to use popen, isn't this based on fork, too?
The reason I want to use popen3 is not that I need stdin/stderr, but
that there is a clean way to pass arguments without having to build a
command line (potential escaping problems etc.).--
Posted via http://www.ruby-forum.com/\.
LSAPI does its own preforking of Rails processes and disconnects and reconnects the database handles after every fork. The way they manage ruby processes causes weird issues like the one you are seeing. The manager code that does the fork management is closed source so it's hard to know exactly what is going on in there.
Cheers-
-- Ezra Zygmuntowicz-- Lead Rails Evangelist
-- ez@engineyard.com
-- Engine Yard, Serious Rails Hosting
-- (866) 518-YARD (9273)
On Mar 4, 2007, at 1:33 PM, Andreas Schwarz wrote:
On Mon, 5 Mar 2007, Andreas Schwarz wrote:
OK, we figured out what is wrong. "reopen" method need to be defined for
"LSAPI" class since popen3 calls "reopen". LSAPI new release will
address this.
However, the root cause of broken MySQL connection is not LSAPI's fault,
actually a bug in ruby's "open3.rb", the fix is like:
def popen3(*cmd)
pw = IO::pipe # pipe[0] for read, pipe[1] for write
pr = IO::pipe
pe = IO::pipe
pid = fork{
# child
fork{
# grandchild
+ begin
pw[1].close
STDIN.reopen(pw[0])
pw[0].close
pr[0].close
STDOUT.reopen(pr[1])
pr[1].close
pe[0].close
STDERR.reopen(pe[1])
pe[1].close
exec(*cmd)
+ ensure
+ exit!(0)
+ end
}
exit!(0)
}
pw[0].close
pr[1].close
pe[1].close
Process.waitpid(pid)
pi = [pw[1], pr[0], pe[0]]
pw[1].sync = true
if defined? yield
begin
return yield(*pi)
ensure
pi.each{|p| p.close unless p.closed?}
end
end
pi
end
module_function :popen3
end
Whenever an error raise in the grandchild process, this process will not
be terminated properly, and DB connection was closed in this process,
thus the DB connection error in the main process. It happens to both
mongrel and LSAPI.
With above fix, DB connection is in good shape even without the LSAPI
fix, just the command was not getting executed.
Best Regards,
George Wang
http://www.litespeedtech.com/
--
Posted via http://www.ruby-forum.com/.
It's all under a BSD-looking license:
gem install ruby-lsapi
jeremy
On 3/4/07, Ezra Zygmuntowicz <ezmobius@gmail.com> wrote:
LSAPI does its own preforking of Rails processes and disconnects
and
reconnects the database handles after every fork. The way they manage
ruby processes causes weird issues like the one you are seeing. The
manager code that does the fork management is closed source so it's
hard to know exactly what is going on in there.
You're right, my bad. I didn't realize they distributed the C code that does the management as well.
-- Ezra Zygmuntowicz-- Lead Rails Evangelist
-- ez@engineyard.com
-- Engine Yard, Serious Rails Hosting
-- (866) 518-YARD (9273)
On Mar 4, 2007, at 3:45 PM, Jeremy Kemper wrote:
On 3/4/07, Ezra Zygmuntowicz <ezmobius@gmail.com> wrote:
LSAPI does its own preforking of Rails processes and disconnects
and
reconnects the database handles after every fork. The way they manage
ruby processes causes weird issues like the one you are seeing. The
manager code that does the fork management is closed source so it's
hard to know exactly what is going on in there.It's all under a BSD-looking license:
gem install ruby-lsapijeremy