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Postings from January 2001
At 12:11 PM 1/21/01 +0000, Alan Burlison wrote:
>Note that even if we used C++ it wouldn't help us in this case, because
>although C++ does exceptions, it knows nothing about threads, mutexes or
>CVs. I suspect the perl6 interpreter loop will look something like:
>
> while (! end of script) {
> if (at cancellation point) {
> if (signal detected)
> call script signal handler;
> if (something died)
> rollback stack;
> } else {
> do next OP;
> }
> }
I'm waffling between checking between every op, or having an op that
explicitly checks. (Possibly the end-of-statement cleanup op would do this)
>In other words the C level signal handler will have to do no more than
>setting a flag, as will the implementation of die(). By cancellation
>point I mean somewhere that is defined as 'safe', i.e. not holding any
>mutexes or waiting on any CVs etc.
I'm not sure the core should really care about that. It's arguably not the
interpreter's problem. (Though it's not a strong argument)
> I suspect a reasonable thing might
>be to have a special 'Now it is safe' opcode that is put out by the
>compiler at the appropriate places. It would be nice if this
>corresponded to a syntactic boundary such as an entire statement, so
>that for example
>
> my $a = $b * $c / $d;
>
>was guaranteed to either to be fully evaluated or not at all.
The question, then, is what do we do with function calls in there (say, $a
= $b + foo()), and what about really long running statements like:
$a = $b + 12 while 1;
Dan
--------------------------------------"it's like this"-------------------
Dan Sugalski even samurai
dan@sidhe.org have teddy bears and even
teddy bears get drunk
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