[plt-scheme] scheme_check_threads gives Bus error on OS X

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Sun Nov 6 08:58:28 EST 2005

At Sun, 06 Nov 2005 00:27:11 -0500, Jon Rafkind wrote:
> While trying to use a C library with MzScheme I have found 
> scheme_check_threads as a way to run MzScheme while inside the Cocoa 
> NSApplication main event loop. Calling scheme_check_threads results in a 
> Bus error, however. The setup involved is irrelevant, I think, as I have 
> reduced the problem to a simple example. This is with MzScheme 299.400 
> built from source.

The bus error results from MzScheme trying to call
scheme_wakeup_on_input(), but your application doesn't set it. I'll
change MzScheme to make setting scheme_wakeup_on_input optional, and
you can avoid the problem meanwhile by setting scheme_wakeup_on_input
to a function that does nothing.

On the other hand, if you're not setting scheme_wakeup_on_input and
instead relying on busy-waiting, you probably just want
scheme_thread_block(0.0) to let other threads run.

With either implementation, beware that calling the Cocoa API from
other MzScheme threads probably won't work. MzScheme thread swapping is
implemented by copying and overwriting the C stack. This means that if
any other MzScheme thread calls into the Cocoa API, Cocoa may notice
that the stack isn't consistent with the active event loop.


Posted on the users mailing list.