MPW Shell -- Bugs and Conflicts

For Mac OS 8 only (9 and X not affected):

If you use Apple's MPW Shell, you need to know about the following bugs:

• CloseView: If you have Apple's CloseView 7.2.1, which came with Mac OS 8.0, get rid of it. When activated, CloseView overwrites memory which it does not own but which MPW Shell uses, and the very next time you use certain MPW Shell commands (notably Search and StreamEdit), your computer will freeze.
• Menu Bar Crash: If you select 57 or more characters in an MPW Shell window and then click anywhere in the menu bar, MPW Shell crashes. The crash does not terminate any other programs, but it disables cascading menus in all other applications until you reboot. I suspect the crash happens because of this chain of logic: At the instant you click in the menu bar, MPW copies the top worksheet window's selection into the "File > Open Selection" menu item, which is statically allocated to hold no more than 64 bytes. For example, if you select the word "myfile," the menu item becomes
  
      Open "myfile"
  
  which you'll notice is 7 bytes longer than the selection. All of which means that if your selection is 57 bytes or more, MPW Shell overfills that 64 byte area and overwrites something sensitive.
  

  Important: If you are trying to re-create this crash on your computer, remember: To select the text, do not triple-click, which selects the whole line. The crash does not occur if the selection includes a newline, because then the menu item becomes simply
  
      Open Selection
  
  Instead, try pasting the next line into any worksheet, and double click on the word in the middle:

  -> 123456789012345678901234567890123456789012345678901234567890 <-

  How to Avoid Triggering This Bug: Whenever using MPW Shell, cultivate the habit of clicking (to deselect the text) in any window that has a long line of text selected. Once you do this, clicking in the menu bar becomes safe. I once thought that this habit would be difficult to learn, but it's one of the easiest, most automatic habits I've ever formed.

These bugs are present in MPW Shell versions 3.4 and 3.5.

The author uses a "G1" Macintosh (a Power Mac 6100) for word processing and in-house C++ programming. He thought the 6100 was just God-forsakenly unstable until he discovered these two undocumented bugs.

This article is for all you fans of lowendmac.com.

• Home

Copyright © 2003-2007  J. E. Brown   all rights reserved.
feedback: write me here
P. O. Box 1368
Los Alamos, NM USA 87544-1368