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From: Lew <lewbloch@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Volatile keyword
Date: Mon, 12 Dec 2011 06:34:18 -0800 (PST)
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On Monday, December 12, 2011 4:51:41 AM UTC-8, rap...@gmail.com wrote:
> Does this make all read/writes happen in full.
> 
> For example, if one thread had
> 
> volatile long a = 0xFFFFFFFF00000000L;
> 
> <do stuff>
> 
> a = ~a;
> 
> If another thread read a, would it always give 0xFFFFFFFF00000000 or
> 0x00000000FFFFFFFF and not partial writes (say it updates 32 bits and
> then the next 32 bits).
> 
> I understand that if two threads do a++, it might only increment
> twice, if they both read the old value at the same time.
> 
> Effectively, does the CPU lock the entire 64-bits for the long when
> doing the write update, and so other threads either seen the updated
> value or the old value?

http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.4
http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.7
http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.3.1.4

-- 
Lew