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    <p>In this case you need to use <em>safe publication idioms</em> when making your object available to other threads, namely (from <a href="http://jcip.net/" rel="noreferrer">Java Concurrency in Practice</a>):</p> <blockquote> <ul> <li>Initializing an object reference from a static initializer;</li> <li>Storing a reference to it into a volatile field or AtomicReference;</li> <li>Storing a reference to it into a final field of a properly constructed object; or</li> <li>Storing a reference to it into a field that is properly guarded by a lock.</li> </ul> </blockquote> <p>If you use safe publication, you don't need to declare fields <code>volatile</code>. </p> <p>However, if you don't use it, <strong>declaring fields <code>volatile</code> (theoretically) won't help</strong>, because memory barriers incurred by <code>volatile</code> are one-side: volatile write can be reordered with non-volatile actions after it.</p> <p>So, <code>volatile</code> ensures correctness in the following case:</p> <pre><code>class Foo { public int x; } volatile Foo foo; // Thread 1 Foo f = new Foo(); f.x = 42; foo = f; // Safe publication via volatile reference // Thread 2 if (foo != null) System.out.println(foo.x); // Guaranteed to see 42 </code></pre> <p>but don't work in this case:</p> <pre><code>class Foo { public volatile int x; } Foo foo; // Thread 1 Foo f = new Foo(); // Volatile doesn't prevent reordering of the following actions!!! f.x = 42; foo = f; // Thread 2 if (foo != null) System.out.println(foo.x); // NOT guaranteed to see 42, // since f.x = 42 can happen after foo = f </code></pre> <p>From the theoretical point of view, in the first sample there is a transitive happens-before relationship </p> <pre><code>f.x = 42 happens before foo = f happens before read of foo.x </code></pre> <p>In the second example <code>f.x = 42</code> and read of <code>foo.x</code> are not linked by happens-before relationship, therefore they can be executed in any order.</p>
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    1. POJava: Caching of non-volatile variables by different threads
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    1. COSorry, I did not get your statment "declaring fields volatile (theoretically) won't help, because memory barriers icurred by volatile are one-side." Could you please explain what does "one-side" mean? Thank you.
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    2. COI think it is clear that the poster does none of these things and wants to know if his code is safe. `Safe publication` seems to be derived practices from the Java concurrency model in JLS chapter 17.
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    3. CO@Dime: I made examples more clear.
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