Re: What does volatile guarantee?
On 13-02-2010 15:34, Mike Schilling wrote:
Lew wrote:
Eric Sosman wrote:
The machines I'm familiar with distinguish 32- and 64-bit
"modes" only by the way addresses are generated, handled, and
mapped. 64-bit load and store instructions are available no
matter what the addresses look like, and are atomic (given
proper operand alignment).
The JLS does not guarantee the atomicity of 'long' and 'double'
accesses absent volatility or other sychronization. /Au contraire/:
http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.7
A fact that's IMHO of little practical consequence. If the value isn't
shared, this doesn't matter. If it is shared, volatility or other
sychronization is already required for sensible behavior. Admittedly it can
lead to bizarre behavior when one thread sets a long to -1 and another to 0,
and the result is that every once in a great while its value is 2**32 - 1..
Very true.
synchronized is good!
Arne
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