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Re^7: How does CATCH_SET optimize efficiency?

by PerlOnTheWay (Scribe)
on Dec 18, 2012 at 01:16 UTC ( #1009260=note: print w/ replies, xml ) Need Help??


in reply to Re^6: How does CATCH_SET optimize efficiency?
in thread How does CATCH_SET optimize efficiency?

Dave, thanks, this clarify things a lot!

So when there're multiple evals in a FETCH, and an exception is triggered, it will always restart from right after the first eval, no matter what, as only the first eval actually does JMPENV_PUSH, is it right?


Comment on Re^7: How does CATCH_SET optimize efficiency?
Re^8: How does CATCH_SET optimize efficiency?
by dave_the_m (Parson) on Dec 18, 2012 at 12:39 UTC
    In something like
    sub FETCH { eval { $x++ } $x--; eval { die } print; }
    The first eval pushes a new setjmp and runops loop. The inc, dec and die ops are executed within that loop. The die causes a longjmp, which unwinds the C stack, destroying the inner runops loop, and returns control to the exception handler set up by the first call to entertry. That code 'restarts' the op by calling runops(), which executes the print and any remaining ops in FETCH. When FETCH returns, runops() exits, and control is passed back (again) to entertry's exception handler, which this time just immediately returns, passing control to the the middle runops loop, which also immediately returns, and control passes back to the code which handles tied variables.

    Dave.

      So the net effect is that when there's no eval in FETCH, a JMPENV_PUSH is saved, but when there is eval, a run loop is wasted(3 vs 2), is this right?

        Yes.

        Dave.

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