RE: JavaMemoryModel: Re: SoftReference not thread-safe ?

From: David Holmes (
Date: Wed Jan 19 2005 - 18:45:40 EST

Hanson char wrote:
> Is it true that
> 1) the value of "clock" is set by the Garbage Collector,
> 2) so we can assume that this is a stop-the-world event, i.e. only the
> GC runs, and no-one else.
> 3) If we then have several threads that concurrently call get() then
> they should all be set to the same value ?

No. One thread could have read half of clock when it is preempted. A GC
occurs that updates clock. When the original thread resumes it gets a
half-old and half-new timestamp value.

However, given the timestamp is only a hint as to the order in which the GC
might choose to release soft-references, I don't see that the usage
semantics are affected by having a junk timestamp value.

David Holmes

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