Re: 4 week-old pretest bugs

[Richard Stallman]

    Some, but the root cause is still unknown.  It seems UNBLOCK_INPUT gets 
called 
    more than BLOCK_INPUT, so the counter goes below zero and Emacs aborts (in 
    UNBLOCK_INPUT).

It is easy to see how a function could return failing to do
UNBLOCK_INPUT, which would cause the opposite problem.  However, it is
hard to see how anything could do UNBLOCK_INPUT without BLOCK_INPUT.
Perhaps an ugly control flow might bypass the BLOCK_INPUT and not
bypass the corresponding UNBLOCK_INPUT.

Misuse of TOTALLY_UNBLOCK_INPUT or UNBLOCK_INPUT_TO could cause this
problem.

UNBLOCK_INPUT_TO is used in unwind_to_catch.  Maybe there is a way you
can arrange to record how recently unwind_to_catch was last called.
If you create a counter, and have code that gets called fairly often
increment it, you could make unwind_to_catch record the counter values
of the last 10 times it was called.  Maybe that would enable you
to tell whether unwind_to_catch plays a role in this bug.