# Strange interference between LSAPI, popen3 and MySQL **URL:** \ **Category:** Ruby\ **Created:** [March 4, 2007, 7:39pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640 "2007-03-04T19:39:49Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 4, 2007, 7:39pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/1 "2007-03-04T19:39:49Z")
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 ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 4, 2007, 7:57pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/2 "2007-03-04T19:57:35Z")
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. ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 4, 2007, 8:50pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/3 "2007-03-04T20:50:39Z")
On Mon, 5 Mar 2007, Andreas S. 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? 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](http://www.linuxjournal.com/article/7922) 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 ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 4, 2007, 9:43pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/4 "2007-03-04T21:43:02Z")
> > 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 > end > > in 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 ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 4, 2007, 10:13pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/5 "2007-03-04T22:13:48Z")
On Mon, 5 Mar 2007, Andreas S. wrote: > 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. > > ``` > > 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… > 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://rubyforge.org/frs/?group_id=1024&release_id=7721) [http://codeforpeople.com/lib/ruby/systemu/systemu-1.0.0/README](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 ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 4, 2007, 10:33pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/6 "2007-03-04T22:33:06Z")
Ara wrote: > On Mon, 5 Mar 2007, Andreas S. 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://rubyforge.org/frs/?group_id=1024&release_id=7721) > [http://codeforpeople.com/lib/ruby/systemu/systemu-1.0.0/README](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.). ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 5, 2007, 12:17am UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/7 "2007-03-05T00:17:03Z")
Hi~ On Mar 4, 2007, at 1:33 PM, Andreas S. wrote: > I grepped for at\_exit in the LSAPI source code, but didn’t find > > > up db > > 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.). > > – > Posted via [http://www.ruby-forum.com/](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 Z. – Lead Rails Evangelist – removed\_email\_address@domain.invalid – Engine Y., Serious Rails Hosting – (866) 518-YARD (9273) ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 5, 2007, 12:46am UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/8 "2007-03-05T00:46:10Z")
On 3/4/07, Ezra Z. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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-lsapi jeremy ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 5, 2007, 1:16am UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/9 "2007-03-05T01:16:13Z")
On Mar 4, 2007, at 3:45 PM, Jeremy K. wrote: > It’s all under a BSD-looking license: > gem install ruby-lsapi > > jeremy You’re right, my bad. I didn’t realize they distributed the C code that does the management as well. – Ezra Z. – Lead Rails Evangelist – removed\_email\_address@domain.invalid – Engine Y., Serious Rails Hosting – (866) 518-YARD (9273) ---
**Author:** ![andreas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ee7513/32.png) [@andreas](https://www.ruby-forum.com/u/andreas)\ **Post date:** [March 9, 2007, 9:37pm UTC](https://www.ruby-forum.com/t/strange-interference-between-lsapi-popen3-and-mysql/87640/10 "2007-03-09T21:37:42Z")
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 W. > **[LiteSpeed | Internet. Accelerated. - LiteSpeed Technologies](https://www.litespeedtech.com/)** > > LiteSpeed provides one-stop web-acceleration solutions that embrace and advance cutting-edge technologies. Web server, load balancer, cache solutions, and more.