RE: JavaMemoryModel: Question about implementation of java.util.concurrent.ConcurrentHashMap

From: Sylvia Else (
Date: Thu Nov 13 2003 - 22:56:36 EST

At 02:33 PM 14/11/2003, Evan Ireland wrote:
>Does anyone know how much, for example, a full read barrier at
>volatile read costs compared with just fetching the one volatile
>from main memory?

This question has arisen here recently in a slightly different context,
because I was concerned about it.

The answer is really that you cannot assume that reading a volatile with
these memory model semantics necessarily involves the high cost of flushing
a cache. The memory cache implementors are able to provide solutions that
avoid this for the significant occurrences, and make volatile reads quite


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