[Openmcl-devel] creating a daemon

Eric Blood eblood at winkywooster.org
Mon Jul 5 08:36:51 PDT 2004

[Long post follows]

I am trying to create an application to run as a daemon at machine
startup.  It is going to include allegro serve, swank, and some of my
own components.  Here is my starting point:

    ;;;  openmcl -l astest.lisp -e '(make-server)'

    (eval-when (:compile-toplevel :load-toplevel :execute)
      (require :aserve)
      (require :swank))

    (in-package :cl-user)

    (defclass server-application (ccl::lisp-development-system)

    (defmethod ccl::toplevel-function ((app server-application) 
      (declare (ignore init-file))
      (swank:create-server :port 8001 :dont-close t)
      (net.aserve:start :port 8000)
      (process-suspend *current-process*))

    (defun make-server ()
      (ccl:save-application "aserver"
	                   :application-class (find-class 'server-application)
                            :prepend-kernel t))

First question, is doing a process suspend on the Initial process at
the end of the toplevel-function a good thing?  If I don't, the
toplevel-function will be repeatedly called.  This is mostly
working--swank is opening a port, but not responding to the inital
handshake, but I am looking into that.

To go a step further, what is the best way to disassociate lisp from
the terminal?  Forcibly close the 0, 1, and 2 file descriptors?  Or,
is there something I can do with *terminal-io*.

I also have been playing around with forking the process:

    (defun fork-test (&optional exit)
      (let ((pid (#_getpid)))
        (dotimes (n 5)
          (format t "~A: ~A" pid n)
          (sleep 1)))
      (when exit
        (#_exit 0)))

The two things that I observe is that the output from the parent
process is displayed over 5 seconds, and then the child process's
output follows immediately afterward.  Some sort of locking?  And if I
exit from the parent process, both the parent and child close.  Is
this behavior also terminal related?  If so, I can understand the
blocking of the child output, but why would the child process exit
when the parent process exits?

    Welcome to OpenMCL Version (Beta: Darwin) 0.14.2-p1!
    ? (fork-test)
    1959: 0
    1959: 1
    1959: 2
    1959: 3
    1959: 4
    ? 1961: 0                           <-- at this point the ouput of 
the child
    1961: 1                                 shows immediately
    1961: 2
    1961: 3
    1961: 4
    ? (fork-test t)                     <-- run tests, but have the 
parent exit
    1959: 0
    1959: 1
    1959: 2
    1959: 3
    1959: 4


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