From: gwtmp01@...
Date: 2005-06-27T00:53:04+09:00
Subject: Re: speeding up Process.detach frequency


On Jun 26, 2005, at 6:28 AM, Yukihiro Matsumoto wrote:
> In message "Re: speeding up Process.detach frequency"
>     on Sun, 26 Jun 2005 13:39:35 +0900, nobu.nokada@softhome.net  
> writes:
> |> |It seems like a bug of Process.detach.  After it received the
> |> |termination, it unnecessarily waits for one second again.
> |>
> |> Right.  But using rb_waitpid() withouth WNOHANG does busy-wait.
> |
> |It should check periodically once per 0.06sec in
> |rb_thread_polling().
>
> Isn't it too often for most of the cases?


If the goal is simply to prevent zombie processes, then Process#detach
should just do a double fork.  Here is an implementation of that
technique along with a couple other issues that are common when
creating a detached process (a daemon in Unix terminology):

   def Process.daemon(dir="/")
     return nil unless pid = fork {
       setsid        # become session leader of new session group
       fork {
         # second fork, ensures child is *not* the session leader
         # then throw away references to the terminal or any other
         # redirections.
         [$stdin, $stdout, $stderr].each { |io| io.close }
         Dir.chdir(dir);
         File.umask(0)
         yield if block_given?
       }
       exit(0)
     }
     wait(pid)
   end

Standard practice is for a daemon is to close all open file
descriptors and then reopen what files are relevent for
the daemon (log files usually).  Above I just closed stdin/out/err.
You could loop through all the open files and close them.
This method will make it easy to reopen stdin/stdout/stderr
to the locations expected by the daemon:

   def Process.reopen(stdin=nil, stdout=nil, stderr=stdout)
     $stdin = File.open(stdin || "/dev/null", "r")
     $stdout = File.open(stdout || "/dev/null", "w")
     $stderr = File.open(stderr || "/dev/null", "w")
   end

Here is an example of using these two calls

   Process.daemon {
     Process.reopen(nil, "/tmp/logfile")
     sleep 5;
     puts "this goes to /tmp/logfile"
   }

The interface to reopen could be different.


Gary Wright