Using redirection for a simple process controller

 
/* ------------------------------------------------------------------ */
/* This is a simple process controller in REXX.                       */
/* It starts one or more programs and restarts them if they end.      */
/*                                                                    */
/* It uses the redirection of the handle 3 into a file as semaphore   */
/* to check if the program is still running.                          */
/* (Hint: You can use all handles from 1 to 9 for this purpose;       */
/*        handle 0 is the handle for STDIN)                           */
/*                                                                    */
/* Note also that this method does _not_ work for all programs, for   */
/* example VIEW.EXE in OS/2 WARP 4!                                   */
/*                                                                    */
/*                                                                    */
/* (c) 1996 Bernd Schemmer, Germany, EMail: Bernd.Schemmer@gmx.de     */
/*                                                                    */

                    /* get the name of this program                   */
  parse source . . thisProgram

                    /* install an error handler for CTRL-BREAK        */
  signal on halt

  call log "Initializing ..."

                    /* load the neccessary REXXUTIL functions         */
  call rxFuncAdd "SysLoadFuncs", "REXXUTIL", "SysLoadFuncs"
  call SysLoadFuncs

                    /* stem with the programs to start                */
  programsToStart.0 = 0
  i = programsToStart.0

                    /* The entry for VIEW.EXE does _not_ work in      */
                    /* OS/2 WARP 4!!!                                 */
  i=i+1;
  programsToStart.i.Name =      "VIEW.EXE"      /* program name       */
  programsToStart.i.Parameter = "CMDREF.INF"    /* program parameter  */
  programsToStart.i.SemFile =   "$$VIEW$$"      /* "semaphore" file   */

                    /* Note:                                          */
                    /* Use special code to get the names for the      */
                    /* semaphore files if you want to run this        */
                    /* program more than ones at the same time!!!     */
                    /* (e.g. use the routine GetTempFile from RXT&T)  */

  i=i+1;
  programsToStart.i.Name =      "E.EXE"
  programsToStart.i.Parameter = ""
  programsToStart.i.SemFile =   "$$E$$"

  i=i+1;
  programsToStart.i.Name =      "ICONEDIT.EXE"
  programsToStart.i.Parameter = ""
  programsToStart.i.SemFile =   "$$ICON$$"

  programsToStart.0 = i

                    /* get the directory for the "semaphore" files    */
  tempDir = value( "TEMP",, "OS2ENVIRONMENT" )
  if tempDir = "" then
    tempDir = value( "TMP",, "OS2ENVIRONMENT" )
  if tempDir = "" then
    tempDir = ".\"

  if right( tempDir,1 ) <> "\" then
    tempDir = tempDir || "\"

  call log "Starting the programs ..."

                    /* marker for the initial round                   */
  firstRound = 1

                    /* no. of processes started in the initial round  */
  programsStarted = 0


  do forever

    do i = 1 to programsToStart.0
      curProgram = programsToStart.i.name
      curParams = programsToStart.i.Parameter
      curSemFile = tempDir || programsToStart.i.SemFile

                    /* ignore empty entries                           */
      if curProgram = "" then
        iterate

                    /* check, if we can write to the semaphore file   */
      if stream( curSemFile, "c", "OPEN WRITE" ) = "READY:" then
      do
                    /* we can write to the semaphore file ->          */
                    /* program seems not to be running                */
        call stream curSemFile, "c", "CLOSE"

        if firstRound = 0 then
        do
                    /* program ended for misc. reason -> restart it   */
          call log "Program """ || curProgram || """ ended. "
          call log "Restarting the program: " || curProgram
          call log "Parameter are: " || curParams
        end /* if firstRound = 0 then */
        else
        do
                    /* program not yet started -> start it            */
          call log "Starting the program: " || curProgram
          call log "Parameter are: " || curParams
        end /* else */

                    /* start/restart the program                      */
                    /* (redirect handle 3 into the "semaphore" file)  */
        "@start " curProgram curParams "3>" || curSemFile

        if stream( curSemFile, "c", "OPEN WRITE" ) = "READY:" then
        do
                    /* error starting the program                     */
          call stream curSemFile, "c", "CLOSE"

          call log "Error starting """ || curProgram || """"
          call log "Now ignoring the program " || curProgram
          programsToStart.i.name = ""

        end /* if stream( curSemFile, "c", "OPEN WRITE" ) = "READY:" then */
        else
          if firstRound = 1 then
            programsStarted = programsStarted +1

      end /* if stream( curSemFile, "c", "OPEN WRITE" ) = "READY:" then */
      else
      do
        if firstRound <> 0 then
        do
                    /* cannot use the semaphore file                  */
          call log "Error using the semaphore file " || curSemFile
          call log "Now ignoring the program " || curProgram
          programsToStart.i.name = ""

        end /* if firstRound <> 0 then */

      end /* else */

    end /* do i = 1 to programsToStart.0  */

    if firstRound = 1 then
      if programsStarted = 0 then
      do
        call log "Could not start any of the programs!"
        call log "Program ends."
        leave
      end /* if programsStarted = 0 then */
      else
        call log programsStarted || " program(s) started."

    firstRound = 0

                    /* wait 2 seconds before we check again           */
    call SysSleep 2

  end /* do forever */

exit

/* ------------------------------------------------------------------ */
log: PROCEDURE expose thisProgram
  parse arg message

  say "[" || fileSpec( "N", thisProgram ) || " - " || ,
      date() time() || "]" message
RETURN

/* ------------------------------------------------------------------ */
/* error handler for CTRL-BREAK                                       */
halt:

  call log "CTRL-BREAK received. Doing housekeeping ..."
  call log "Press any key after closing all programs started from " || ,
       thisprogram || " ..."
  "@PAUSE >NUL"

  call log "Deleting the semaphore files ... "
  do i = 1 to programsToStart.0
    curSemFile = tempDir || programsToStart.i.SemFile
    curProgram = programsToStart.i.name

    if curProgram <> "" then
    do
      call log "Deleting " || curSemFile
      "@del " curSemFile "2>NUL 1>NUL"
      if rc <> 0 then
      do
        call log "Error " || rc || " deleting " || curSemFile
        call log "(Maybe " || curProgram || " is still running.)"
      end /* if rc <> 0 then */
    end /* if curProgram <> "" then */

  end /* do i = 1 to programsToStart.0 */

  call log "Program ended."
exit 0
/* ------------------------------------------------------------------ */