Re: Core dumps in redisplay.

[David Kastrup]

"Jan D." <address@hidden> writes:

>> Also with regard to the other report you answered (where I was wrong):
>> I might well be mistaken.  I am just trying to get a hold of why Emacs
>> keeps crashing on me.  It appears, anyway, that something seriously
>> elusive is going on here.  I'll probably have to implement some kind
>> of trace buffering for interrupt_input_block in order to get a hold of
>> what is happening here.
>>
>> I already disassembled stuff because I thought the compiler might be
>> at fault.  Maybe I should also try without optimization.
>
>
> If you configured with GTK, there is a possibility that multiple
> threads are updating interrupt_input_block.  I've tried to handle that
> situation, but bugs may of course still remain.

How did you try to handle it?  Basically, we have the following
accesses to interrupt_input_blocked:

BLOCK_INPUT increases it
UNBLOCK_INPUT decreases it
TOTALLY_UNBLOCK_INPUT resets it
throws reset it to the state at the time of the catch

The last two options would behave really badly in the presence of
multithreading.

There must only be one thread touching interrupt_input_blocked, or we
get into trouble.  I don't see that we can sensibly handle the case
"reset to state at the time of the catch" in any manner with two
threads accessing the variable.  We need one variable per thread then,
and the input is blocked if either variable is nonzero.  Only a
per-thread variable can be reset to a meaningful value.

Could you elaborate on what happens here in parallel threads?  I can't
imagine that one can execute Lisp sanely in two threads, so one thread
would be likely C-only?  Why would that thread have to meddle with
interrupt_input_blocked at all?

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum