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POJava: Caching of non-volatile variables by different threads
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  1. POJava: Caching of non-volatile variables by different threads
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    copied!<p>The situation is the following:</p> <ol> <li>I have an object with lots of setters and getters.</li> <li>Instance of this object is created in a one particular thread where all values are set. Initially I create an "empty" object using new statement and only then I call some setters methods based on some complicated legacy logic.</li> <li>Only then this object became available to all other threads that use only getters.</li> </ol> <p><strong>The question:</strong> Do I have to make all variables of this class volatile or not?</p> <p>Concerns:</p> <ul> <li>Creation of a new instance of the object and setting all its values is separated in time. </li> <li>But all other threads have no idea about this new instance until all values are set. So other threads shall not have a cache of not fully initialized object. Isn't it?</li> </ul> <p><em>Note:</em> I am aware about builder pattern, but I cannot apply it there for several other reasons :(</p> <p><strong>EDITED:</strong> As I feel two answers from Mathias and axtavt do not match very well, I would like to add an example:</p> <p>Let's say we have a <code>foo</code> class:</p> <pre><code>class Foo { public int x=0; } </code></pre> <p>and two threads are using it as described above:</p> <pre><code> // Thread 1 init the value: Foo f = new Foo(); f.x = 5; values.add(f); // Publication via thread-safe collection like Vector or Collections.synchronizedList(new ArrayList(...)) or ConcurrentHashMap?. // Thread 2 if (values.size()&gt;0){ System.out.println(values.get(0).x); // always 5 ? } </code></pre> <p>As I understood Mathias, it can print out 0 on some JVM according to JLS. As I understood axtavt it will always print 5.</p> <p>What is your opinion?</p> <p>-- Regards, Dmitriy</p>
 

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