DO NOT REPLY [Bug 21720] New: - Memory/logger leak with multiple VelocityEngine instances

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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=21720

Memory/logger leak with multiple VelocityEngine instances

           Summary: Memory/logger leak with multiple VelocityEngine
                    instances
           Product: Velocity
           Version: 1.3.1
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: Critical
          Priority: Other
         Component: Source
        AssignedTo: velocity-dev@jakarta.apache.org
        ReportedBy: beatty@physics.umass.edu


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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