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https://issues.apache.org/jira/browse/OFBIZ-5395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15093765#comment-15093765
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Jacques Le Roux commented on OFBIZ-5395:
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Just an update about Java Regular Expression Library Benchmarks in 2015 at
https://www.voxxed.com/blog/2016/01/java-regular-expression-library-benchmarks-2015
(http://tusker.org/regex/regex_benchmark.html used in this issue description
was in 2010)
Also at
http://www.javaadvent.com/2015/12/java-regular-expression-library-benchmarks-2015.html
(hopefully one of them will be available at long term...)
> Introduce Tomcat's JreMemoryLeakPreventionListener and why
> ----------------------------------------------------------
>
> Key: OFBIZ-5395
> URL: https://issues.apache.org/jira/browse/OFBIZ-5395
> Project: OFBiz
> Issue Type: Improvement
> Components: framework
> Affects Versions: Trunk
> Reporter: Jacques Le Roux
> Assignee: Jacques Le Roux
> Labels: JreMemoryLeakPreventionListener, ThreadLocal, leak
> Fix For: Trunk
>
> Attachments: OFBIZ-5395-CompilerMatcher.patch
>
>
> After reading few articles on possible memory leaks when using ThreadLocal
> variable with custom classes in application server context where a thread
> pool is used, I checked OFBiz code. There is only 2 custom classes
> concerned: CompilerMatcher and RollbackOnlyCause (JDK classes are not
> concerned by ThreadLocal memory leaks).
> First I must tell, that the memory leak problem is more clearly described in
> those articles when you use an external Application Server (like Tomcat) and
> you deploy/undeploy applications. It seems there are no major issues when you
> use OFBiz OOTB (with Tomcat embedded). Nevertheless, it's a concern by and
> large.
> I have not investigated RollbackOnlyCause, only CompilerMatcher. But, after
> some profiling, I believe both should only generate small amouts of memory
> leaks, almost not noticeable even after several deploy/undeploy cycles.
> Nevertheless I tried to find a good way to get rid of CompilerMatcher
> possible leaks. I thought about 3 ways:
> # *Reverts [CompilerMatcher related
> changes|http://svn.apache.org/viewvc?view=revision&revision=1075322]* done
> for OFBIZ-4107 (introduction of CompilerMatcher) by using
> Perl5Compiler.READ_ONLY_MASK which guarantees thread safety
> ** Pros: no need to introduce ThreadLocal
> ** Cons: performance, local Perl5 variables creation removes the
> patterns-compiled-cache CompilerMatcher introduced (note: [I found the origin
> of CompilerMatcher class
> here|http://mail-archives.apache.org/mod_mbox/jmeter-user/200212.mbox/%3cse0ae21c....@katun.com%3E])
> # *Uses ThreadLocal<CompilerMatcher> local variables* instead of private
> static members
> ** Pros: no need to worry about thread safety
> ** Cons: performance, local ThreadLocal local variables creation removes the
> patterns-compiled-cache ThreadLocal<CompilerMatcher> offers when used as a
> private static member
> # *Introduces [Tomcat's
> JreMemoryLeakPreventionListener|http://wiki.apache.org/tomcat/MemoryLeakProtection].*
> [What it does (in less than a
> minute)?|http://stackoverflow.com/questions/14882794/what-does-tomcats-threadlocalleakpreventionlistener-do-exactly]
> [Why JreMemoryLeakPreventionListener was
> created?|http://www.tomcatexpert.com/blog/2010/04/06/tomcats-new-memory-leak-prevention-and-detection]
> [History (29 pages
> presentation).|http://people.apache.org/~markt/presentations/2010-11-04-Memory-Leaks-60mins.pdf]
> How it does it? [Read
> code!|http://svn.apache.org/viewvc/tomcat/trunk/java/org/apache/catalina/core/JreMemoryLeakPreventionListener.java?view=annotate]
> ** Pros:
> *** no changes related to CompilerMatcher, performance enhancement the cache
> introduces kept
> *** prevents memory leaks when an external Application Server is used or at
> least warn about them (Note: this can only be done in OFBiz internally, for
> app server the best is to document with a section in the [related wiki
> page|https://cwiki.apache.org/confluence/display/OFBTECH/Run+OFBiz+under+outside+Application+Servers].
> ** Cons: none, this should had any noticeable effects when OFBiz is used OOTB
> (Tomcat embedded)
> I decided to go with the JreMemoryLeakPreventionListener solution. Another
> reason for that is that when I profiled OFBiz trunk using the demo site I
> found that we were having a large bloc of memory retained by
> [sun.awt.AppContext|http://www.docjar.com/docs/api/sun/awt/AppContext.html].
> I think we should not have such a thing, the web truk demo does not use AWT
> at all! Fortunately jreMemoryLeakPreventionListener.setAppContextProtection
> prevents this, even if I have still no ideas from where this comes (certainly
> something like explainded in page 14 of the link from "History (29 pages
> presentation)" above)
> I'm also considering to replace the current uses of java.util.regex.Pattern
> by CompilerMatcher in cases of a static pattern is used. When the
> CompilerMatcher cache makes sense (patterns do not change). The interest is
> the better performance of the oro framework, at least so far (Java 1.6, see
> below).
> Some interesting references I noted while analysing this issue:
> * [Oro is 6 times faster than regular Java
> regex|http://www.tusker.org/regex/regex_benchmark.html]. So, with its cache,
> CompilerMatcher is more than an interesting alternative to regular Java regex.
> * Java regex Javadoc:
> [Compiler|https://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html],
>
> [Matcher|https://docs.oracle.com/javase/6/docs/api/java/util/regex/Matcher.html]
> * Oro Javadoc:
> [Compiler|https://jakarta.apache.org/oro/api/org/apache/oro/text/regex/Perl5Compiler.html],
>
> [Matcher|https://jakarta.apache.org/oro/api/org/apache/oro/text/regex/Perl5Matcher.html]
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