Re: Volatile happens before question

From:

Knute Johnson <nospam@knutejohnson.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 17 Jan 2012 15:46:12 -0800

Message-ID:

<jf5184$r9f$1@dont-email.me>

On 1/17/2012 10:10 AM, markspace wrote:

On 1/17/2012 9:21 AM, Knute Johnson wrote:

And if b = 1 could be reordered before a = true then b would be flopping
all over the place because as soon as a = true b would again have to
be 0.

But those reads and writes could be reordered, couldn't they? The read
of "a" could happen after the read of "b", because there's no
happens-before relationship there (a is not volatile, nor synchronized
in any way).

Or is that what you are saying? The actual problem is worse. (And I did
in fact fubar my explanation and the my reading of the code. It *is*
broken though.) I'm still looking for references, and I might be close.
Uno momento....

In his case b cannot be anything but 0 in thread 2 when a is read in the
if statement. That doesn't mean it is going to stay that way very long.

And to quote Goetz "When a field is declared volatile, the compiler and
runtime are put on notice that this variable is shared and that
operations on it should not be reordered with other memory operations."

--

Knute Johnson