[jrugged] r282 committed - Deleted wiki page InitializerThreadSafetyExample1 through web user int...

[jru...@googlecode.com]

Revision: 282
Author: joseph.r...@gmail.com
Date: Thu Nov 22 06:07:05 2012
Log: Deleted wiki page InitializerThreadSafetyExample1 through web
user interface.
http://code.google.com/p/jrugged/source/detail?r=282

Deleted:
/wiki/InitializerThreadSafetyExample1.wiki

=======================================
--- /wiki/InitializerThreadSafetyExample1.wiki Wed Jan 4 07:12:42 2012
+++ /dev/null
@@ -1,112 +0,0 @@
-#summary An example of a potential gotcha when using the Initializer in
jrugged.
-{{{
-package org.fishwife.jrugged;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.fail;
-
-import org.junit.Test;
-
-/**
- * Starting a thread within an object constructor is an anti-pattern. See
Java Concurrency In Practice. The Java memory
- * model does not guarantee that the fields of an object will contain
correct references until the constructor
- * returns. But the Initializer _requires_ you to publish a reference to
the Initializable _during_ object construction
- * (before the constructor returns). This means Initializer's background
thread can see the wrong references. Calling
- * the initializer as the last method in the constructor will not help
because:
- *
- * 1. The java memory model does not guarantee that an object's final
fields are initialized until after the constructor
- * completes.
- *
- * 2. A sub-class can perform may have more constructor logic after the
initializer is invoked.
- *
- * Rather than starting threads in the constructor, the recommended
practice is to create
- * a separate initialize() method that is invoked on an object _after_ it
is fully constructed, meaning all the java
- * memory model guarantees are in place. The initialize() method can then
delegate to Initializer . . . within certain
- * constraints as shown by InitializerThreadSafetyExample2.
- *
- * If you are willing to deal with the potential exceptions/nulls, it is
possible to wait (as this example shows)
- * for the object construction to be complete.
- *
- * This test should print the following (or something similar):
- *
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Found null value for final field!
- * Constructor finished so populating values
- * Set status to Status.UP
- */
-public class TestInitializerThreadSafety1 {
- @Test(timeout = 1000)
- public void threadSafety() throws Exception {
- Service testable = new Service();
-
- while (Status.INIT == testable.status) { }
-
- for (int valIdx = 0; valIdx < testable.values.length;
valIdx++ ) {
- assertEquals(Integer.toString(valIdx), valIdx,
testable.values[valIdx]);
- }
- }
-
- private static class Service implements Initializable {
-
- private volatile Status status = Status.INIT;
-
- /**
- * The java memory model guarantees final references are
set only after the constructor completes. But Initializer
- * requires the "this" reference to escape _during_ object
construction. This means the background thread is given a
- * reference to a partially constructed object.
- */
- private final long[] values;
-
- private Initializer initializer;
-
- public Service() {
-
- initializer = new Initializer(this);
-
- initializer.setRetryMillis(10);
- initializer.initialize();
-
- try {
- Thread.sleep(100);
- } catch (InterruptedException e) {
- fail("Should not happen");
- }
-
- values = new long[16834];
- }
-
- @Override
- public void tryInit() throws Exception {
- if (null == values) {
-
- System.out.println("Found null value for
final field!");
-
- throw new NullPointerException();
-
- } else {
-
- System.out.println("Constructor finished
so populating values");
-
- for (int i = 0; i < values.length; i++) {
- values[i] = i;
- }
- }
- }
-
- @Override
- public void afterInit() {
- status = Status.UP;
-
- System.out.println("Set status to Status.UP");
- }
- }
-}
-}}}