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    <p>Yes, it is guaranteed that thread 2 will print "done" . Of course, that is if the write to <code>b</code> in Thread 1 actually happens before the read from <code>b</code> in Thread 2, rather than happening at the same time, or earlier!</p> <p>The heart of the reasoning here is the <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.4.5"><em>happens-before relationship</em></a>. Multithreaded program executions are seen as being made of events. Events can be related by happens-before relationships, which say that one event happens before another. Even if two events are not directly related, if you can trace a chain of happens-before relationships from one event to another, then you can say that one happens before the other.</p> <p>In your case, you have the following events:</p> <ul> <li>Thread 1 writes to <code>s</code></li> <li>Thread 1 writes to <code>b</code></li> <li>Thread 2 reads from <code>b</code></li> <li>Thread 2 reads from <code>s</code></li> </ul> <p>And the following rules come into play:</p> <ul> <li>"If x and y are actions of the same thread and x comes before y in program order, then hb(x, y)." (the <em>program order</em> rule)</li> <li>"A write to a volatile field (§8.3.1.4) happens-before every subsequent read of that field." (the <em>volatile</em> rule)</li> </ul> <p>The following happens-before relationships therefore exist:</p> <ul> <li><em>Thread 1 writes to <code>s</code></em> happens before <em>Thread 1 writes to <code>b</code></em> (program order rule)</li> <li><em>Thread 1 writes to <code>b</code></em> happens before <em>Thread 2 reads from <code>b</code></em> (volatile rule)</li> <li><em>Thread 2 reads from <code>b</code></em> happens before <em>Thread 2 reads from <code>s</code></em> (program order rule)</li> </ul> <p>If you follow that chain, you can see that as a result:</p> <ul> <li><em>Thread 1 writes to <code>s</code></em> happens before <em>Thread 2 reads from <code>s</code></em></li> </ul>
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    1. POHappens-before relationships with volatile fields and synchronized blocks in Java - and their impact on non-volatile variables?
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    1. COI don't see where this documentation states that if `a` is assigned before some `volatile` variable `b` then both variables are synchronized between two threads. Is there something in the data model that says the when a `volatile` variable is modified all other variables are synchronized between the threads as opposed to just the one `volatile` variable?
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    2. COIndeed there is! I have expanded my answer to attempt to explain this. Apologies for posting the answer without the explanation; i was dragged off to a meeting.
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    3. COAh. OK. So the `happens before` rule applies to all variables (volatile or not) between threads on one variable is volatile. Thanks. Learn something new every day.
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