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POin what architectures/OS other thread can see default nonfinal field values after constructor call?
 

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  1. POin what architectures/OS other thread can see default nonfinal field values after constructor call?
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    <p>I'm trying to reproduce a memory visibility issue in case of insufficient object initialization for non-final fields (JLS <a href="http://docs.oracle.com/javase/specs/jls/se5.0/html/memory.html#17.5" rel="nofollow noreferrer">17.5 Final Field Semantics</a>, <a href="http://docs.oracle.com/javase/specs/jls/se5.0/html/memory.html#65124" rel="nofollow noreferrer">FinalFieldExample</a> class example). Where it stated "However, f.y is not final; the reader() method is therefore not guaranteed to see the value 4 for it"</p> <p>I've tried this code:</p> <pre><code>public class ReorderingTest2 { public static void main(String[] args) { for (int i = 0; i &lt; 2500; i++) { new Thread(new Reader(i)).start(); new Thread(new Writer(i)).start(); } } static class Reader implements Runnable { private String name; Reader(int i) { this.name = "reader" + i; } @Override public void run() { //System.out.println(name + " started"); while (true) { FinalFieldExample.reader(name); } } } static class Writer implements Runnable { private String name; Writer(int i) { this.name = "writer" + i; } @Override public void run() { //System.out.println(name + " started"); while (true) { FinalFieldExample.writer(); } } } static class FinalFieldExample { int x; int y; static FinalFieldExample f; public FinalFieldExample() { x = 3; y = 4; } static void writer() { f = new FinalFieldExample(); } static void reader(String name) { if (f != null) { int i = f.x; int j = f.y; if (i != 3 || j != 4) { System.out.printf("reader %s sees it!%n", name); } } } } } </code></pre> <p>As in <a href="https://stackoverflow.com/questions/6264466/jvm-reordering-visibility-effect-test">previous my similar topic</a> - I've tried on different PCs (from 2 to 8 cores) with Windows and even on our server-side Solaris 32 core box - I couldn't reproduce it: f.x and f.y - are always already proper-initialized.</p> <p>For Intel/x86/x64 architecture as <a href="https://stackoverflow.com/questions/6264466/jvm-reordering-visibility-effect-test/6265793#6265793">I got the answer</a> - they have pretty much <a href="http://bartoszmilewski.wordpress.com/2008/11/05/who-ordered-memory-fences-on-an-x86/" rel="nofollow noreferrer">default memery guarantees</a> which prevent such constructor logic reordering. Seems the same is true for Solaris/sparc too?</p> <p>So in what architecture/OSes this reordering can be reproduced? </p>
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    1. CObtw you dont need so many threads (unless you do have the cores) and you have a datarace in reader. basically the reader can see 2 different instances of `f`. As for the question, I guess Azul can be a possible answer since it has the weakest model (x86 has one of the strongest). The other one could be anything running on IA-64.
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    2. COEdit: I dont know if the test is good since accessing 'f' will always hit the cache (the reference it's always the same location) but reading off it probably won't. Perhaps you'd like large object spanning more than a single cache line as well.
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    3. COI've tried 2 or 8 cycles instead of 2500 (you can try quickly) - no change. Data races don't matter, this null check is actually against NPE before first `f` assignment, then it just test whether object where `f` point to is fully initialized, no matter if it is new object or the same as in null check... And I tried large objects in the http://stackoverflow.com/questions/6264466/jvm-reordering-visibility-effect-test
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