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POCan I assume 'no data race' between user thread and finalize thread in Java
 

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  1. POCan I assume 'no data race' between user thread and finalize thread in Java
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    <p>Consider the following Java class:</p> <pre><code>class X { public void foo() { bar = 1; } protected void finalize() { if (bar == 1) baz(); } private int bar = 0; } </code></pre> <p>Under the assumption that <code>X.foo()</code> is never called from any <code>finalize()</code> method (directly or indirectly), can I be sure that the code above is free of data-races, that is, can I be sure that <code>X.finalize()</code> sees the value written by <code>X.foo()</code> in every case where <code>X.foo()</code> is actually called?</p> <p>The naive analysis would say that <code>X.finalize()</code> cannot run concurrently with <code>X.foo()</code> (due to the mentioned assumption), so no extra synchronization is necessary.</p> <p>I would guess that the code above is free of data races, but it troubles me that the language specification contains the following explicit statement in <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.4.5" rel="nofollow">§17.4.5</a>, but says nothing about a happens-before relationship between finalize() and methods in general:</p> <blockquote> <p>There is a happens-before edge from the end of a constructor of an object to the start of a finalizer (§12.6) for that object.</p> </blockquote> <p><strong>EDIT:</strong> I see the need to make my question more precise, so here is an attempt at a precise reformulation of the question:</p> <p>Does Java guarantee a <em>happens-before</em> relation between a specific method <code>X.foo()</code> and <code>X.finalize()</code> if I guarantee that <code>X.foo()</code> is never called (directly or indirectly) from any <code>finalize()</code> method? Here, <em>happens-before</em> is to be interpreted exactly as defined in <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.4.5" rel="nofollow">§17.4.5</a>.</p>
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    1. USKristian Spangsege
    1. USKristian Spangsege
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    1. COWhat if the finalizer contains other code before the `if`? In general that code might bring the object into scope again which could mean that other threads would have access to it again. But I'm entirely sure about this; I'm highly interested in seeing if anybody can verify or disprove my comment.
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      1. USViktor Seifert
    2. COYou bring up a very important point that I was not sufficiently aware of. The case where `X.finalize()` contains code that resurrects the instance is not interesting to me (because I control that part of the code, and I know I don't resurrect anything). However, it seems that resurrection can happen in other ways that are outside my control. For example, an application could have a finalizer that resurrects an instance of `X`.
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      1. USKristian Spangsege
 

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