TOPS-20 Commands Reference Manual

CONTINUE

Continues execution of a fork that was halted.

Format

@CONTINUE (FORK) argument /switch

where:

argument

is the fork name or fork number.

Default - the current fork

/switch

is a keyword, chosen from the list below, indicating your choice of CONTINUE command options.

CONTINUE Command Switches

/BACKGROUND	keeps your terminal at TOPS-20 command level and continues execution of the program in a "background" fork. When the program attempts to do terminal input or output, it halts and displays the message [FORK-NAME wants the TTY].
/NORMALLY	restores your terminal to command level (if any) within the program. Default
/STAY	keeps your terminal at TOPS-20 command level and continues execution of the program in a "background" fork. Output from the program is sent to the terminal and is intermixed with whatever output is currently displayed. When the program attempts to read from the terminal, it can randomly intercept input intended for the EXEC or another program. Therefore, use this switch with programs that, once started, do not request further terminal input.

Characteristics

Continuing a Noncurrent Fork

When you continue a noncurrent fork, by including the fork-name argument in a CONTINUE command, the specified fork becomes your current fork.

Hints

Stopping a Background Program

To stop a background program, give the FREEZE command.

Providing Input to a Background Program

A background program, continued with CONTINUE /BACKGROUND, sends the message [FORK-NAME wants the TTY] when it wants input. A background program, continued with CONTINUE /STAY, prints the program prompt, for example PASCAL>, when it wants input. To (provide input to a program that is running in a background fork, return to program command level with CONTINUE /NORMALLY. (Some programs require you to type an extra RETURN after CONTINUE /NORMALLY to display the program prompt). Then, type the required program input. (See below, Restrictions, Programs Competing for Terminal Input.)

Monitoring your Program

CONTINUE /STAY and CONTINUE /BACKGROUND, by keeping your terminal at TOPS-20 command level (EXEC), let you use TOPS-20 commands to monitor the progress of your program while it is running. Use the INFORMATION FORK-STATUS command to display the CPU time used and the kept and RUN status of each fork belonging to the current EXEC level. More commands for monitoring your programs are listed below in Related Commands.

Running Multiple Programs Simultaneously

To simultaneously run multiple programs in background forks or use commands that affect memory, use one or a combination of the following methods after placing a fork in the background with CONTINUE /STAY or CONTINUE /BACKGROUND:

PUSHing to an Inferior EXEC Level: Type the PUSH command to create an inferior EXEC level and a fresh copy of memory (address space). Then run another program and return to EXEC command level with CONTINUE /STAY or CONTINUE /BACKGROUND. The new program does not affect the background program since both programs are at a different EXEC level. However, see Restrictions below. PUSH to a new EXEC before running each new program.
KEEPing the Fork: Type the KEEP command to give the background fork a "kept" status. (A kept fork is not cleared from memory when another program is loaded.) Then run another program and return to EXEC command level with CONTINUE /STAY or CONTINUE /BACKGROUND. KEEP each background fork before running another program. Check the status of your forks with INFORMATION FORK-STATUS.

Continuing Forks Using the Fork Name

You can continue a fork by typing the fork name as if it were the CONTINUE command. To function as the CONTINUE command, the fork must be "kept" with the KEEP or the SET PROGRAM KEEP command. For more information, refer to the descriptions of these commands.

More Information

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

Restrictions

Similar Programs Competing for Files

If you have two similar programs running simultaneously, they may try to access the same files at the same time (for example, temporary files labeled by job number, used by compilers). This may cause unpredictable situations to develop. To avoid the possibility, run different kinds of programs.

Programs Competing for Terminal Input

If you use CONTINUE /STAY to run a program in a background fork, the program can request input from the terminal while you are giving input to the EXEC or another program. This input can be randomly intercepted by the background program when it requests terminal input. Usually though, the EXEC or the current program receives the input.

When terminal input is intercepted by the background program, the program will usually type input error messages. To give input to the program, stop the program by typing two CTRL/Cs or the program's exit command. Then, if the background program is at a higher EXEC command level, give POP commands to return to the EXEC level that holds the background program. (POP terminates the current EXEC and erases programs in its memory.) Finally, give the CONTINUE /NORMALLY command; this puts you at program command level so that you can give the requested input.

Remember, input is intercepted by the background program randomly. Therefore, you may have to type extra CTRL/Cs, program exit commands, and POPs. To reduce confusion about the direction of terminal input, it is recommended that you use CONTINUE /STAY only when you plan to work at the current EXEC level while a program runs in a background fork. You should also CONTINUE /STAY programs that simply end without requesting terminal input. Use CONTINUE /BACKGROUND when you plan to work at a lower EXEC level or at another program command level.

When a program started with CONTINUE /BACKGROUND requests terminal input, it sends the message, [FORK-NAME wants the TTY]. No input is taken by the background program until you return to program command level with CONTINUE /NORMALLY. You should CONTINUE /BACKGROUND programs that request terminal input.

Maintaining Access to Directories

While a fork is running in the background, use caution in using the CONNECT, ACCESS and END-ACCESS commands. Changing your directory access could leave the fork unable to reference certain files.

No I/O Control with Some Programs

Most programs read and write data to the terminal through standard input and output designators. Some programs however, use different methods of communicating with the terminal. Therefore, when you use /BACKGROUND and /STAY to control terminal input and output from a background fork, the input and output behavior of programs with nonstandard designators can be unpredictable.

Continued Programs Do Not Prompt for input

When you continue a program, the program continues from exactly where it was interrupted. If the program was waiting for input, it will simply continue to wait for input; it won't prompt you again. For example, assume you are running the DECmail/MS program and you press CTRL/C at the MS> prompt. Next, you CONTINUE MS. The cursor moves to the next line but no MS> prompt appears. This is because MS has continued to do the last thing it was doing when you interrrupted it with CTRL/C - waiting for a command at the MS> prompt. MS does not know that its prompt is no longer displayed before the cursor.

So, when you continue a program and nothing happens, consider what you were doing when you CTRL/C'd the program. If you were at the MS> prompt, type an MS command or, press RETURN again to redisplay the MS> prompt. If you had typed a portion of and MS command, press CTRL/R to redisplay the command. If you had typed a portion of a mail message, press CTRL/K to redisplay the message.

Effect on Memory and Terminal

The CONTINUE /NORMALLY command resumes processing the program in memory, and leaves your terminal at program command level (if any). The CONTINUE /BACKGROUND and CONTINUE /STAY commands resume processing the program in memory, but leave your terminal at TOPS-20 command level.

Related Commands

DETACH CONTINUE	for disengaging your current job from your terminal and continuing the program that the job is running
FORK	for changing the current fork
FREEZE	for halting a program in a background fork
INFORMATION FILE-STATUS	for monitoring files being written by your program
INFORMATION FORK-STATUS	for displaying the number and the status of each fork in your job
INFORMATION MEMORY-USAGE	for monitoring your program's use of memory
INFORMATION PROGRAM-STATUS	for monitoring your program's use of CPU time
KEEP	for giving a fork a kept status
PUSH	for obtaining a lower TOPS-20 command level (and a fresh copy of memory)
REENTER	for starting your current program at its alternate entry point (if any)
START	for starting your current program at the beginning
RESET, SET NAME, SET PROGRAM, UNKEEP	other multiforking-class commands for performing related functions

Examples

Display the fork status with the INFORMATION FORK-STATUS command. Notice that the arrow points to the current fork. Then, give the CONTINUE command to continue the program in the current, halted fork.
```
@INFORMATION FORK-STATUS
   EDIT (1): Kept, HALT at 6253, 0:02:54.4
=> DUMPER (2): HALT at 700304, 0:01:19.3
@CONTINUE
DUMPER>
```
Run the DSR program and then halt it by typing two CTRL/Cs. Give the CONTINUE /BACKGROUND command to continue DSR in a background fork and return to EXEC command level. Then, give the KEEP command so that you can load another program without clearing the running, background, DSR fork. Check the status of DSR with the INFORMATION FORK-STATUS command.
```
@RUN DSR
DSR>TEST.RNO
^C
@CONTINUE /BACKGROUND
@KEEP
[Keeping DSR]
@INFORMATION FORK-STATUS
=> DSR (1): Kept, Background, Running at 413160, 0:00:00.8
```
Now begin editing a file with the EDIT program. During your editing session the system notifies you that the background fork wants input. To return to DSR command level, first exit the edit program. Then check the fork status with the INFORMATION FORK-STATUS command. Notice that DSR is in a terminal I/O wait state and that EDIT is now the current fork. Since the fork you want to continue is not the current fork, you must specify the fork name with the CONTINUE command. Now type CONTINUE DSR.
```
@EDIT COMAND.CMD
Edit: COMAND.CMD.2
*P
00100   SET DEFAULT PRINT /NOHEADER /NOTIFY:YES
00200   SET PROGRAM MS KEEP START
00300   SET PROGRAM HOST KEEP CONTINUE
00400   SET DEFAULT COMPILE-SWTICHES PAS /NOFLAG-NON-STANDARD
00500   INFO MAIL
00600   TAKE
*I350
00350   SET PROGRAM DUMPER KEEP CONTINUE
DSR>[DSR: wants the TTY]
*E

[COMAND.CMD.3]
@INFORMATION FORK-STATUS
=> EDIT (1): Kept, HALT at 6253, 0:00:51.4
   DSR (1): Kept, Background, TTY I/O wait at 4404426,
0:00:00.8
@CONTINUE DSR

DSR>
```

Begin editing a long file, giving the F (find) command to EDIT. Give a CTRL/C and then the M command to return to TOPS-20 command level. Give the CONTINUE /STAY command and then INFORMATION FILE-STATUS commands to check the progress of EDIT as it searches through the file. (Notice that the byte position shown in response to successive INFORMATION FILE-STATUS commands grows larger.) Finally, give the CONTINUE command to return to EDIT so you can give more EDIT program commands.

@EDIT DOC-PLAN.MEM
Edit: DOC-PLAN.MEM.1
*FABCD$
Yes? (Type H for help): M
@CONTINUE /STAY
@INFORMATION FILE-STATUS
 Connected to PS:<LATTA>,  JFNS:
 4   <LOADTEST>EDIT.EXE.4        Read, Execute
 3   EDIT-BUFFER.OUT.100046      Read, Write, 0.(7)
 2   DOC-PLAN.MEM.1      Read, 43520.(7)
 1   <SYSTEM>EXEC.EXE.153        Read, Execute

 Device assigned to/opened by this job: TTY222

@INFORMATION FILE-STATUS 2
 2   DOC-PLAN.MEM.1      Read, 112640.(7)
@INFORMATION FILE-STATUS 2
 2   DOC-PLAN.MEM.1      Read, 130560.(7)
@CONTINUE

*

Start compiling a long file. After compilation has begun, type two CTRL/Cs to stop the compilation and return to the EXEC command level. Use the CONTINUE /STAY command to resume compilation, and then PUSH to a new EXEC command level. Edit a text file at this lower level, then give the POP and CONTINUE commands to return to the compilation in progress. The compiler finishes, in this case, after you have done so.
```
@COMPILE DUMPER.MAC
MACRO:  DUMPER
^C
@CONTINUE /STAY
@PUSH

 TOPS-20 Command processor 7(55)
@EDIT PROFIL.TXT
Edit: PROFIL.TXT.2
*SAPRIL$JUNE$^:*
00100   JUNE 19, 1987
00500   JUNE 12
00750   JUNE 5
00900   JUNE 18
01400   JUNE 21
*E

[PROFIL.TXT.3}
@POP
@CONTINUE

EXIT
```

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