Re: JavaMemoryModel: init methods

From: Jeffrey G. Bogda (
Date: Mon Oct 02 2000 - 19:34:03 EDT

"Boehm, Hans" wrote:

> It seems to me it's unattainable for most large programs. There are too
> many ways to cheat and get better performance. And some of the more
> interesting cheats are even correct, e.g. updating a cache with an atomic
> pointer assignment and not locking on lookup, or "or"ing boolean results by
> initializing a global to "false" and then asynchronously writing "true" into
> it, potentially from multiple threads. Even if the program in question
> doesn't care enough about performance to do this, one if the library writers
> will have.

It sounds to me like you are saying that properly synchronized programs are
possible, but people aren't going to write them. I agree with you, but I think
it is unfortunate. I would rather see programmers and library writers fully
synchronize their shared data and let the compiler and run-time system worry
about "cheating" in order to improve performance. I guess the only way that is
going to happen is if they fully trust the compiler and run-time system or if
the language somehow requires proper synchronization.

> I think we agree. But it seems to me that this is almost exactly what you
> need to do to remove the synchronization in the beans example? You need to
> recognize that field values are constant once the object becomes public, and
> then remove the synchronization on the bean from field accesses, eventhough
> the bean is accessible from multiple threads? Or did I misunderstand?

In some situations I think it should be possible to detect this. It seems like
you have a particular scenario in mind. Can you give some sample code?


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