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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] [Created] (LUCENE-3334) IOUtils.closeSafely should use log suppressed Exceptions in stack trace of original Exception (a new feature of Java 7)
Date Fri, 22 Jul 2011 21:52:09 GMT
IOUtils.closeSafely should use log suppressed Exceptions in stack trace of original Exception
(a new feature of Java 7)
-----------------------------------------------------------------------------------------------------------------------

                 Key: LUCENE-3334
                 URL: https://issues.apache.org/jira/browse/LUCENE-3334
             Project: Lucene - Java
          Issue Type: Improvement
          Components: core/other
            Reporter: Uwe Schindler
            Assignee: Uwe Schindler
            Priority: Minor
         Attachments: LUCENE-3334.patch

I was always against Java 6 support, as it brings no really helpful new features into Lucene.
But there are several things that make life easier in coming Java 7 (hopefully on July 28th,
2011). One of those is simplier Exception handling and suppression on Closeable, called "Try-With-Resources"
(see http://docs.google.com/View?id=ddv8ts74_3fs7483dp, by the way all Lucene classes support
these semantics in Java 7 automatically, the cool try-code below would work e.g. for IndexWriter,
TokenStreams,...).

We already have this functionality in Lucene since adding the IOUtils.closeSafely() utility
(which can be removed when Java 7 is the minimum requirement of Lucene - maybe in 10 years):

{code:java}
try (Closeable a = new ...; Closeable b = new ...) {
  ... use Closeables ...
} catch (Exception e) {
  dosomething;
  throw e;
}
{code}

This code will close a and b in an autogenerated finally block and supress any exception.
This is identical to our IOUtils.closeSafely:

{code:java}
Exception priorException = null;
Closeable a,b;
try (Closeable a = new ...; Closeable b = new ...) {
  a = new ...;
  b = new ...
  ... use Closeables ...
} catch (Exception e) {
  priorException = e;
  dosomething;
} finally {
  IOUtils.closeSafely(priorException, a, b);
}
{code}

So this means we have the same functionality without Java 7, but there is one thing that makes
logging/debugging much nicer:
The above Java 7 code also adds maybe suppressed Exceptions in those Closeables to the priorException,
so when you print the stacktrace, it not only shows the stacktrace of the original Exception,
it also prints all Exceptions that were suppressed to throw this Exception (all Closeable.close()
failures):

{noformat}
org.apache.lucene.util.TestIOUtils$TestException: BASE-EXCEPTION
    at org.apache.lucene.util.TestIOUtils.testSuppressedExceptions(TestIOUtils.java:61)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.rules.TestWatchman$1.evaluate(TestWatchman.java:48)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)
    at org.apache.lucene.util.LuceneTestCase$LuceneTestCaseRunner.runChild(LuceneTestCase.java:1486)
    at org.apache.lucene.util.LuceneTestCase$LuceneTestCaseRunner.runChild(LuceneTestCase.java:1404)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at junit.framework.JUnit4TestAdapter.run(JUnit4TestAdapter.java:39)
    at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:420)
    at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:911)
    at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:768)
    Suppressed: java.io.IOException: TEST-IO-EXCEPTION-1
            at org.apache.lucene.util.TestIOUtils$BrokenCloseable.close(TestIOUtils.java:36)
            at org.apache.lucene.util.IOUtils.closeSafely(IOUtils.java:58)
            at org.apache.lucene.util.TestIOUtils.testSuppressedExceptions(TestIOUtils.java:62)
            ... 26 more
    Suppressed: java.io.IOException: TEST-IO-EXCEPTION-2
            at org.apache.lucene.util.TestIOUtils$BrokenCloseable.close(TestIOUtils.java:36)
            at org.apache.lucene.util.IOUtils.closeSafely(IOUtils.java:58)
            at org.apache.lucene.util.TestIOUtils.testSuppressedExceptions(TestIOUtils.java:62)
            ... 26 more
{noformat}

For this in Java 7 a new method was added to Throwable, that allows logging such suppressed
Exceptions (it is called automatically by the synthetic bytecode emitted by javac). This patch
simply adds this functionality conditionally to IOUtils, so it "registers" all suppressed
Exceptions, if running on Java 7. This is done by reflection: once it looks for this method
in Throwable.class and if found, it invokes it in closeSafely, so the exceptions thrown on
Closeable.close() don't get lost.

This makes debugging much easier and logs all problems that may occur.

This patch does *not* change functionality or behaviour, it just adds more nformation to the
stack trace in a Java-7-way (similar to the way how Java 1.4 added causes). It works here
locally on Java 6 and Java 7, but only Java 7 gets the additional stack traces. For Java 6
nothing changes. Same for Java 5 (if we backport to 3.x).

This would be our first Java 7 improvement (a minor one). Next would be NIO2... - but thats
not easy to do with reflection only, so we have to wait 10 years :-)

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