[jira] Closed: (VELOCITY-193) Memory/logger leak with multiple VelocityEngine instances

["Henning Schmiedehausen (JIRA)" <de...@velocity.apache.org>]

     [ https://issues.apache.org/jira/browse/VELOCITY-193?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Henning Schmiedehausen closed VELOCITY-193.
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> Memory/logger leak with multiple VelocityEngine instances
> ---------------------------------------------------------
>
>                 Key: VELOCITY-193
>                 URL: https://issues.apache.org/jira/browse/VELOCITY-193
>             Project: Velocity
>          Issue Type: Bug
>          Components: Engine
>    Affects Versions: 1.3.1
>         Environment: Operating System: All
> Platform: Macintosh
>            Reporter: Ian Beatty
>            Priority: Critical
>             Fix For: 1.5
>
>         Attachments: VelocityBugIsolator.tgz
>
>
> When creating and then releasing to garbage collection multiple VelocityEngine instances, the 
> instances are apparently not closing out or otherwise letting go of their logger instances. As a 
> result, code that needs to create and destroy several VelocityEngine instances will eventually choke 
> and die. This happens with either Avalon Logkit or Log4j, although the exact nature of the choking 
> differs. This test program isolates the problem:
> import org.apache.velocity.app.VelocityEngine;
> public class IsolateVelocityBug {
> 	static public void main( String[] args ) {
> 		int repCount = Integer.parseInt( args[0] );
> 		for( int i = 0; i < repCount; i++ ) {
> 			System.out.println( "Test repetition " + i + "..." );
> 			try {
> 				final VelocityEngine velocityEngine = new VelocityEngine();
> 				velocityEngine.init();
> 			} catch( Exception e ) {
> 				throw new Error( e );
> 			}
> 		}
> 	}
> }
> Run the program with an integer command-line argument specifying the number of times to cycle 
> through the loop, and make sure velocity-1.3.1.jar, commons-collections.jar, and either an Avalon 
> Logkit or Log4j JAR are on your classpath. (I tested with logkit-1.0.1.jar and log4j-1.1.3.jar.) What 
> *should* happen is that the program completes its specified number of loops, doing nothing but 
> writing "Test repetition" over and over with an incrementing number. What *does* happen, at least 
> on my machine, depends on which logging package is provided for Velocity.
> Using Avalon Logkit 1.0.1, the program runs fine for 252 iterations; on the 253nd, it aborts with 
> the following message:
>     "PANIC : Error configuring AvalonLogSystem : java.io.FileNotFoundException: /Users/ibeatty/
> Development/javaDev/VelocityBugIsolator/velocity.log (Too many open files)"
> Using Log4j 1.1.3, the program runs fine for only one iteration; on the second and any subsequent 
> iterations, it continues but prints out a whole mess of
>     "log4j:ERROR Attempted to append to closed appender named [null].
>      log4j:WARN Not allowed to write to a closed appender."
> That happens for as long as I care to let it run (95 iterations, with something over 800 lines of 
> such errors per iteration by the end).
> To me, it sure looks like Velocity is leaving dangling loggers behind as VelocityEngine instances 
> are created and discarded, and that the two logging systems respond differently to this but both 
> have problems.
> Why, might you ask, should anyone care about making many VelocityEngine instances? I ran into it 
> when developing a major web app using JUnit to build comprehensive test suites. To run 
> independently, every test has to start from scratch, which means getting its own VelocityEngine. 
> Many tests means many instances, and the logging problem kicks in. Running JUnit test suites 
> within Intellij IDEA and using Log4j, the ERROR/WARN messages were more than a nuicanse; 
> eventually, I'd start getting out-of-memory errors, too. These went away when I changed the tests 
> to use a shared VelocityEngine instance (which caused its own set of problems).
> Using binary download of Velocity 1.3.1, which claims to have been created on 2003-04-01.
> I find it hard to believe nobody else has tripped over this before, so maybe it's sensitive to the OS 
> or something. It happened whether I compiled the test code with Javac or Jikes. Using Java 
> 1.4.1_01.

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