Problem with method that starts process, yields pid then yie

Ruby
1

I’m trying to create a method that will kick off a new process, return
it’s pid… while allowing the return code to also be captured for
later examination…
[on windows platform]

class Exec
def process_handler
# if I do the following below, it will yield the
# pid which is great, but because I did not
# write pipe it to {}, I don’t think it’s possible to capture
the return_level
return IO.popen(“ruby -e ‘sleep 2’ &exit 33”).pid
end
end

puts Exec.new.process_handler.to_s # => 3389
puts $? >> 8 # => gives me an error because I didnt start IO.popen with
{}

As a work around, I tried the following:
class Exec
def process_handler
# if I do the following below, it will yield the
# pid which is great, but because I did not
# write pipe it to {}, I don’t think it’s possible to capture
the return_level
Thread.new {
p = IO.popen(“ruby -e ‘sleep 2’ &exit 33”) {}
$p_return_code = $? >> 8
}
return p, $p_return_code
end
end

The problem here is, p will not be defined until the process has
finished writing to the pipe {}, which will prevent the return of the
pid…

Any suggestions on this? I’m not able to test this code as I’m using
a machine @ an internet cafe.

Kind regards,
Chris

2

On Fri, 2 Dec 2005, x1 wrote:

I’m trying to create a method that will kick off a new process, return it’s
pid… while allowing the return code to also be captured for later
examination… [on windows platform]

should work, but untested on windows:

harp:~ > cat a.rb

require “thread”
class Exec
%w( cmd queue pipe pid thread exitstatus ).each{|a| attr_accessor
a}
def initialize cmd
self.cmd = cmd
self.queue = ::Queue::new
self.thread =
::thread::new(queue) do |q|
pipe = ::IO::popen cmd
q.push pipe
q.push pipe.pid
begin
loop{ stdout = pipe.gets or break }
pipe.close
q.push $?.exitstatus
rescue => e
q.push e
end
end
self.pipe = queue.pop
self.pid = queue.pop
self.exitstatus = nil
end
def wait
self.exitstatus = self.queue.pop
end
def self::[](*a, &b) new *a, &b end
end

require “yaml”

y “start” => Time::now
sleep = Exec[ " ruby -e’ sleep 2 and exit 42 ’ " ]
y “cmd” => sleep.cmd
y “pid” => sleep.pid
y “exitstatus” => sleep.wait
y “finish” => Time::now

harp:~ > ruby a.rb

start: 2005-12-02 14:03:29.920649 -07:00

cmd: " ruby -e’ sleep 2 and exit 42 ’ "

pid: 19947

exitstatus: 42

finish: 2005-12-02 14:03:31.930995 -07:00

kind regards.

-a

3

it seems to work!!

Let me spend some time trying to make sense of it… Thanks
soooooooooooooooo much!!!
grins

4

On Sat, 3 Dec 2005, x1 wrote:

it seems to work!!

Let me spend some time trying to make sense of it… Thanks
soooooooooooooooo much!!!
grins

great.

i learned a bit too : didn’t know about pipe.pid

cheers.

-a

5

I’ve hacked at it and managed to learn quite a few things in the
process but I cant seem to assign the Exec class to a DRb server to
handle requests.

Ideally, the would be able to do something like:

DRb.start_service
sleep = DRbObject.new(nil, ‘druby://server:2001’).execute(“ruby -e
‘sleep 3 and exit 43’”)
p sleep.pid
p sleep.wait

I tried everything I could think of but the script kept breaking.
Here’s what I’ve got that DOES work:

require ‘drb’
require ‘thread’

class Execute
%w( cmd queue pipe pid thread exitstatus alive ).each{|a| attr_accessor
a}
def initialize(cmd)
@cmd = cmd
@queue = Queue.new
@thread = Thread.new(queue) do |q|
pipe = IO.popen(cmd)
q.push pipe
q.push pipe.pid
begin
loop{ stdout = pipe.gets or break }
pipe.close
q.push $?.exitstatus
rescue => e
q.push e
end
end
@pipe = queue.pop
@pid = queue.pop
@exitstatus = nil
end
def wait
@exitstatus = @queue.pop
end
end

hostname = hostname.chomp
port = “4501”

#DRb.start_service “druby://#{hostname}:#{port}”, Execute.new
#DRb.thread.join

job = Execute.new(“cmd /c ruby -e ‘sleep 3 and exit 42’”)
puts job.cmd
puts job.pid
puts job.wait

If I uncomment the DRb lines, the server starts but clients throw an
error :frowning:

6

On Sun, 4 Dec 2005, x1 wrote:

I’ve hacked at it and managed to learn quite a few things in the
process but I cant seem to assign the Exec class to a DRb server to
handle requests.

Ideally, the would be able to do something like:

 harp:~ > cat servant.rb
 #! /usr/bin/env ruby
 %w( thread drb socket time yaml ).each{|lib| require lib}

 class Execute
   %w( cmd queue pipe pid thread exitstatus alive ).each{|a|

attr_accessor a}
def initialize(cmd)
@cmd = cmd
@queue = Queue.new
@thread = Thread.new(queue) do |q|
pipe = IO.popen(cmd)
q.push pipe
q.push pipe.pid
begin
loop{ stdout = pipe.gets or break }
pipe.close
q.push $?.exitstatus
rescue => e
q.push e
end
end
@pipe = queue.pop
@pid = queue.pop
@exitstatus = nil
end
def wait
@exitstatus = @queue.pop
end
end

 class Executioner
   def execute cmd
     Execute::new cmd
   end
 end

 mode = ARGV.shift
 hostname = Socket.gethostname
 port = 4501

 case mode
   when %r/server/i
     DRb.start_service "druby://#{ hostname }:#{ port }",

Executioner.new
DRb.thread.join

   when %r/client/i
     DRb.start_service
     executioner = DRbObject.new nil, "druby://#{ hostname }:#{ port

}"
sleep = executioner.execute “ruby -e’ sleep 3 and exit 43 '”
y “start” => Time::now.iso8601
y “pid” => sleep.pid
y “exitstatus” => sleep.wait
y “finish” => Time::now.iso8601
end

 harp:~ > ./servant.rb server &
 [1] 15727



 harp:~ > ./servant.rb client
 ---
 start: "2005-12-03T16:58:19-07:00"
 ---
 pid: 15729
 ---
 exitstatus: 43
 ---
 finish: "2005-12-03T16:58:22-07:00"

hth.

-a

7

What we have so far works, however ideally, printing the pid should
not rely on the completion of the job. The only thing that should rely
on the completion of the job would be outputting the exitstatus.
Here’s my vision…

class JobServer

        def execute(cmd)

                    # kicks off the job and returns the pid

                    return pid

        end

        def status(pid)

                    # returns the status of the job. IE is the pid

alive? or dead?

                    return pid.alive?

        end

        def exitstatus(pid)

                    # returns the exitstatus based on the PID

                    return pid.exitstatus

        end

end

Scenerio: I need to kick off two jobs and a third upon completion of

the first (when exit statis is 0).

Ideally, one would be able to kick off a job with execute() and know

about it’s pid. Then later on, be able to reference the status of that
pid, such as alive? or dead?. If dead, one could call the
exitstatus() method to find out what the return code of that job was.

case mode

        when %r/server/i

                    DRb.start_service "druby://#{ hostname }:#{ port

}",

                    JobServer.new

                    DRb.thread.join

        when %r/client/i

                    DRb.start_service

                    job = DRbObject.new(nil, "druby://#{ hostname

}:#{ port }")

                    pid = job.execute("ruby -e' sleep 3 and exit 43

'")

                    # without having to wait on the execution

above to finish:

                    if job.status(pid) == true

                                puts "exit status = " +

job.existstatus(pid)

                    else

                                puts "job still running"

                    end

end

#Again, this code isnt functional, just a concept of how I would see.
What’s preventing me from turning waht we have into this is my lack of
knowledge in the following w/ your code:

1) not exactly sure attr_accessor does

2) not sure what Queue.new does

3) not sure what def initialize does

Again, I really² appreciate your help in understanding and assistance.

8

weird thing is, with your first example, the pid prints out before the
command finishes… where with the second example, nothing is printed
out until the command exits.

9

On Tue, 6 Dec 2005, x1 wrote:

What we have so far works, however ideally, printing the pid should not rely
on the completion of the job. The only thing that should rely on the
completion of the job would be outputting the exitstatus.

but that is the exactly the case? example:

harp:~ > ruby servant.rb server &
[2] 31570

harp:~ > ruby servant.rb client

start: “2005-12-05T16:29:21-07:00”

pid: 31572

after getting pid…: “2005-12-05T16:29:21-07:00”

exitstatus: 43

finish: “2005-12-05T16:29:24-07:00”

note the times. only getting the exitstatus relies on job
completion (by
definition) and is a blocking operation.

before i read more of your post make sure you understand the above. the
code
again:

harp:~ > cat servant.rb
#! /usr/bin/env ruby
%w( thread drb socket time yaml ).each{|lib| require lib}
class Execute
%w( cmd queue pipe pid thread exitstatus alive ).each{|a|
attr_accessor a}
def initialize(cmd)
@cmd = cmd
@queue = Queue.new
@thread = Thread.new(queue) do |q|
pipe = IO.popen(cmd)
q.push pipe
q.push pipe.pid
begin
loop{ stdout = pipe.gets or break }
pipe.close
q.push $?.exitstatus
rescue => e
q.push e
end
end
@pipe = queue.pop
@pid = queue.pop
@exitstatus = nil
end
def wait
@exitstatus = @queue.pop
end
end
class Executioner
def execute cmd
Execute::new cmd
end
end

mode, hostname, port = ARGV.shift, Socket.gethostname, 4501

case mode
when %r/server/i
DRb.start_service “druby://#{ hostname }:#{ port }”,
Executioner.new
DRb.thread.join

 when %r/client/i
   DRb.start_service
   executioner = DRbObject.new nil, "druby://#{ hostname }:#{ port

}"
sleep = executioner.execute “ruby -e’ sleep 3 and exit 43 '”
y “start” => Time::now.iso8601
y “pid” => sleep.pid
y “after getting pid…” => Time::now.iso8601
y “exitstatus” => sleep.wait
y “finish” => Time::now.iso8601
end

regarding your questions about ‘initialize’ and ‘new’ - ruby is object
orientied. everything is an object constructed from a class. the
method new,
when called on a class returns an object which was created an
initialized
using it’s initialize method. check out the ‘pickaxe’ and the ‘ruby
way’ for
deep insight into ruby - you can’t code without them.

kind regards.

-a

===============================================================================
| ara [dot] t [dot] howard [at] noaa [dot] gov
| all happiness comes from the desire for others to be happy. all misery
| comes from the desire for oneself to be happy.
| – bodhicaryavatara

cat a.rb

10

On Tue, 6 Dec 2005, x1 wrote:

weird thing is, with your first example, the pid prints out before the
command finishes… where with the second example, nothing is printed
out until the command exits.

trying putting

STDOUT.sync = true

at the top of the script.

harp:~ > ruby servant.rb server &

     q.push pipe
   @pid = queue.pop

end
executioner = DRbObject.new nil, “druby://#{ hostname }:#{ port }”
orientied. everything is an object constructed from a class. the method new,
| all happiness comes from the desire for others to be happy. all misery
| comes from the desire for oneself to be happy.
| – bodhicaryavatara

cat a.rb

-a

11

And here’s the results from windows:

Desktop>process.rb client
starting @ Mon Dec 05 20:27:42 Eastern Standard Time 2005
940
Mon Dec 05 20:27:42 Eastern Standard Time 2005
43
Mon Dec 05 20:27:42 Eastern Standard Time 2005
Finished @ Mon Dec 05 20:27:42 Eastern Standard Time 2005

What’s actually happening, is when this is executed:
sleep = executioner.execute “ruby -e’ sleep 3 and exit 43 '”

Windows waits until the job finishes, and then continues to the next
line…(no fork I guess) Just weird how it worked in the original
example…

12

So… I just restarted and booted into SUSE…

The example works perfect under linux… --weird.
To explain what I’m seeing, I added the output of Time.now directly
after printing the pid & exit status…

linux>ruby process.rb client

start: “2005-12-05T20:20:32-05:00”

pid: 7712

x: “2005-12-05T20:20:32-05:00”

exitstatus: 43

x: “2005-12-05T20:20:35-05:00”

finish: “2005-12-05T20:20:35-05:00”

As we see, it instantly gave me the pid and took two seconds to tell
me the exitstatus. (which is what I want) but with windows, it takes 2
seconds to get anything back. I’ll reboot and run the same script in
windows…