Why did we limit the command window history length?

  • Article

In this post: You can hit enter anywhere on the line in the command window, I talked about the command window history.

Daniel asked why the size of the history seems to have a limit of around 256K in VFP9, but no limit in VFP7 (or VFP8).

It was limited to fix this bug report from a customer Oct 2003.

Things to notice about the bug report:

  • It’s just code that can be copy/pasted/run with no fuss
  • It’s a bare minimum of code: not multimegabyte files of code (A 4 GigHz processor can execute about a billion instructions per second. Which one of those billions has the problem?)
  • It clearly demonstrates the issue
  • It says what Observed, and Expected behaviors are

(1) Run these commands from a new .PRG:

COPY FILE HOME(7) + [_COMMAND.PRG] TO HOME(7) + [_COMMAND.mine]

STRTOFILE(REPLICATE([MODIFY COMMAND test]+CHR(13)+ ;

      [MODIFY FORM test]+CHR(13)+[? VERSION()]+CHR(13), ;

      199999),HOME(7) + [_COMMAND.BAK])

o = NEWOBJECT([_shellexecute],HOME() + [\ffc\_environ.vcx])

o.shellexecute(HOME(7),HOME(7),[])

(2) You now have a Windows Explorer window open to your user data directory. Delete _COMMAND.PRG and then rename _COMMAND.BAK to COMMAND.PRG.

(4) Open VFP again...

=== OBSERVED ===

VFP takes a long time to start and when it does, it is using about 325megs of memory.

=== EXPECTED ===

Either a linearly increasing memory usage or limiting _command.prg to a sensible size like 1 MB.

=== COMMENTS ===

To clean up, exit VFP, delete _COMMAND.PRG and rename _command.MINE to _COMMAND.PRG