Thread, fork, wait and popen3

ruby-talk
1

Hi:

I am looking for some hints, or possible a snippet of code that
will solve a little task I am working on.

I would like to launch multiple tasks to a load
balancer, and have the main script wait until
they are all complete. I don’t think this part
is too hard.

If that is not too much trouble, I would like to be
able to identify each task as it completes.

The icing on the cake is that I want to call each
process via popen3 so I can control what is sent
to the std ports.

Thanks for any help.

···

–
Jim Freeze
If only I had something clever to say for my comment…
~

2

Hi,

I would like to launch multiple tasks to a load
balancer, and have the main script wait until
they are all complete. I don’t think this part
is too hard.

If that is not too much trouble, I would like to be
able to identify each task as it completes.

Process.wait(or wait2) returns exited child process ID, it
doesn’t help you?

The icing on the cake is that I want to call each
process via popen3 so I can control what is sent
to the std ports.

Currently, no way to get child’s(really grandchild’s) pid and
its exit status, but I guess you can wait EOF on its stdout and
stderr.

···

At Fri, 19 Jul 2002 10:53:00 +0900, Jim Freeze wrote:

–
Nobu Nakada

3

See:
http://rm-f.net/~cout/ruby/treasures/RubyTreasures-0.4/lib/open3x.rb.html
http://rm-f.net/~cout/ruby/treasures/RubyTreasures-0.4/lib/open3y.rb.html

These are two implementations of popen3 that give you the pid. Open3X
forks and the child process remains in the same process group as the
parent. Open3Y does a double-fork like the original Open3 does.

An alternative is that you might be able to do something like the
following:

@n += 1
unique_string = “Spawning child #{@n} from process #{Process.pid}“
Open3.popen3(”#{cmd} # #{unique_string}”)
str = “ps ax --cols=10000 | grep ‘#{unique_string}’ | grep -v grep | awk ‘{print $1}’” # this could probably be implemented in ruby
child_pid = #{str}

I’ve done this when I needed to find the pid of a process that
daemonizes itself.

Hope this helps,

Paul

···

On Fri, Jul 19, 2002 at 10:53:00AM +0900, Jim Freeze wrote:

The icing on the cake is that I want to call each
process via popen3 so I can control what is sent
to the std ports.

4

Process.wait won’t work well with popen3:

require 'open3’
Open3.popen3(“sleep 10”)
p Process.wait

popen3_test2.rb:4:in `wait’: No child processes (Errno::ECHILD)

from popen3_test2.rb:4

Paul

···

On Fri, Jul 19, 2002 at 11:16:48AM +0900, nobu.nokada@softhome.net wrote:

Process.wait(or wait2) returns exited child process ID, it
doesn’t help you?