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Re: Does perl really need to use sigsetjmp? (18% performancehit)

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Dan Sugalski
January 21, 2001 13:33
Re: Does perl really need to use sigsetjmp? (18% performancehit)
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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;


--------------------------------------"it's like this"-------------------
Dan Sugalski                          even samurai                         have teddy bears and even
                                      teddy bears get drunk

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