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KEEP command

The KEEP command protects a fork from being cleared from memory.


Format

     @KEEP (FORK) fork

     where:

     fork is one of the following:  Fork name
                                    Fork number
                                         Default - the current fork


Characteristics

     Characteristics of Kept Forks

          The KEEP command gives a fork a "kept" status.  A kept  fork
          has these characteristics:

           o  A kept fork is not reset when another program is brought
              into  memory.   Normally,  when  a  program  is  run, it
              replaces the fork currently in memory.  However, if  the
              program in memory is in a kept fork and a new program is
              run, the new program is placed  in  a  new  fork.   This
              allows you to have several programs in memory.

           o  A kept fork is not cleared from memory  with  the  RESET
              command   unless   one   of  these  RESET  arguments  is
              specified:  the fork name, a period or an asterisk.

           o  A kept fork can be restarted by  typing  the  kept  fork
              name  as  an  EXEC  command.   The kept fork name can be
              abbreviated to the point where it is  unique  from  EXEC
              commands  and other kept fork names.  ESCAPE recognition
              and question mark help  also  function  with  kept  fork
              names.

              The KEEP command sets the kept fork to  restart  at  its
              starting  address  when the kept fork name is given as a
              command.  For information on changing the fork's restart
              address  see  Hints,  Setting  the  Kept  Fork's Restart
              Address.

           o  A kept fork is named  after  the  program  it  contains.
              Forks  are  numbered  in  the  order  in which they were
              created.  In multiforking-class commands the  fork  name
              and number are interchangable.


     Inferior Forks

          Any inferior forks created by a kept fork are also kept.


Hints

     Keeping Forks Automatically

          Place  SET  PROGRAM  KEEP  commands  in  your  LOGIN.CMD  or
          COMAND.CMD file for programs that you normally place in kept
          forks.   Then  when  you  load  the  program,   the   system
          automatically  keeps  the  fork  and  notifies  you with the
          message [Keeping FORK-NAME].

          The SET PROGRAM command applies only  to  the  current  EXEC
          level.   If  you  want  your  SET  PROGRAM commands to be in
          effect after a PUSH command,  put  the  commands  into  your
          COMAND.CMD   file.    The   COMAND.CMD   file   is  executed
          automatically after every PUSH command.

     Kept Forks Continued Using the Fork Name

          The KEEP command sets  the  fork  to  be  restarted  at  its
          starting  point  when  the  fork name is given as a command.
          So, if a program that was kept  with  the  KEEP  command  is
          running  in  a  background  fork, and you type the kept fork
          name, execution of the program is canceled and  the  program
          returns to its start address, which is usually the program's
          prompt.

          With the SET PROGRAM KEEP command, you have to  specify  the
          point  at  which the fork will restart when the fork name is
          given as a command.  The starting point can be the program's
          continue,  reentry,  or  start  address.   The  command  SET
          PROGRAM KEEP CONTINUE gives the fork name the same  function
          as  the  CONTINUE  /NORMALLY command.  So, if a program that
          was kept with the  SET  PROGRAM  KEEP  CONTINUE  command  is
          running  in  a  background  fork, and you type the kept fork
          name, execution of the program continues and  your  terminal
          is placed at program level.

     More Information

          The KEEP command is one of  the  TOPS-20  multiforking-class
          commands.   For more information about multiforking, see the
          section Running Multiple  Programs  in  the  TOPS-20  User's
          Guide.


Restrictions

     Limited Number of Forks

          There is a limited number of forks available  on  a  system.
          When  all  forks are in use, existing users cannot add forks
          and new users cannot log in.  Therefore, KEEP only necessary
          forks and return idle forks to the system with the UNKEEP or
          RESET commands.


Related Commands

     INFORMATION FORK-STATUS       for displaying the fork status

     RESET                         for clearing forks from memory

     UNKEEP                        for changing  a  kept  fork  to  an
                                   unkept fork

     CONTINUE, FORK, FREEZE,       other       multiforking-class
     INFORMATION PROGRAM-STATUS,   commands
     SET NAME, and SET PROGRAM


Examples

     1.  Display the fork  status  with  the  INFORMATION  FORK-STATUS
         command.   Then,  give  the  KEEP command to make the current
         fork a kept fork and redisplay the fork status.

         @INFORMATION FORK-STATUS
          => EDIT (1): HALT at 6254, 0:00:00.5
             FILCOM (2): ^C from IO wait at 700272, 0:00:00.3
         @KEEP
         @INFORMATION FORK-STATUS
          => EDIT (1): Kept, HALT at 6254, 0:00:00.5
             FILCOM (2): ^C from IO wait at 700272, 0:00:00.3

     2.  Display the fork status, and  KEEP  the  FILCOM  fork.   Then
         verify the new fork status.

         @INFORMATION FORK-STATUS
          => EDIT (1): Kept, HALT at 6254, 0:00:00.5
             FILCOM (2): ^C from IO wait at 700272, 0:00:00.3
         @KEEP FILCOM
         @INFORMATION FORK-STATUS
          => EDIT (1): Kept, HALT at 6254, 0:00:00.5
             FILCOM (2): Kept, ^C from IO wait at 776721, 0:00:00.3