in reply to Re^36: Why is EO undefined? (More details!)
in thread Why is the execution order of subexpressions undefined?

My definition explicitly allows concurrent derivation of the operands to any non-serialising, binary operator.
Oh, sure, your definition allows it. Noone is questioning that. Your definition isn't the point.

The point being made is that in general, any implementation will effectively be serialized.

You haven't made a convincing argument that the run-time can figure out which parts can be run in parallel, without violating a defined order of execution.

  • Comment on Re^37: Why is EO undefined? (More details!)

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Re^38: Why is EO undefined? (More details!)
by BrowserUk (Patriarch) on Apr 18, 2005 at 13:44 UTC

    The runtime doesn't need to figure anything out.

    If both operands to any, non-serialising, binary operator are non-simple variables (there'd be no chance for concurrency if either is), and the methods which produce those operands are marked (by their authors) as being parallelisable, then the runtime can parallelise them.

    The very fact that they are parallelisable and the programmer has placed them within the same (simple)expression, either side of a non-serialising operator, means that the runtime can call the threaded versions of both methods and wait for them both to complete before continuing.

    But, for that to be workable, the programmer must be able to guarentee the execution order of the derivation of any parameters that will be passed to those two methods.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    Lingua non convalesco, consenesco et abolesco.
    Rule 1 has a caveat! -- Who broke the cabal?
[reply]
      I think we are in violent agreement. Except where the entire universe calls this undefined order of execution, you call it defined order.

      That doesn't matter.

      Since both you, and the rest of the world are saying that you may only write: 

          EXPR1 OP EXPR2

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      if it doesn't matter whether EXPR1 or EXPR2 gets evaluated first.
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[d/l]
        Why are we even continuing this? It is more than a dispute over definitions of terms. BrowserUK refuses to see where the rest of us are comming from. He won't even admit that it is a valid point of view that undefined evaluation order is *a* correct manner of specifying parallelism.
[reply]

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