Re: JavaMemoryModel: Another software-only solution

From: Joel Jones (
Date: Fri Jul 02 1999 - 12:06:06 EDT

First an introduction:

I am Joel Jones, a PhD student at the University of Illinois at
Urbana-Champaign. My research is on annotating Java .class files in a
machine-independent fashion to support machine-dependent optimizations in a
modified JVM JIT. I am on this mailing list because in my quest for
understanding exactly what optimizations are thread-safe, I found chapter
17 less than enlightening.

Raymie Stata <> stated:

> The more ordering constraints there are in the JMM semantics, the
> harder those semantics will be to implement on relaxed-order
> architectures such as Alpha, PowerPC, and IA-64. This observation
> primarily affects two requirements being considered for the JMM
> semantics: that the JMM semantics preserve Java's safety guarantees,
> and that the JMM semantics support the synchronization-free
> initialize-then-publish programming idiom. There's clear consensus
> that preserving the safety guarantees must be a requirement, no
> matter the difficulties that requirement poses on relaxed-order
> architectures. There is no consensus on whether the
> initialize-then-publish idiom is so important that it must be
> supported despite the implementation difficulties it poses on
> relaxed-order machines.

I would support this, with a slight change --- add efficiently after "to
implement" in the first sentence. These architectures provide enough
synchronization primitives to ensure everything grinds to a single
sequentially consistent thread.

Joel Jones PressPot: Annotating Java for Performance

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