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From Kris Schneider <k...@dotech.com>
Subject Re: Memory Leak in ELEvaluator (cont'd...)
Date Sun, 27 Feb 2005 18:50:41 GMT
Or just use the setAccessible hack:

elcache.jsp:
------------
<%@ page import="java.io.*" %>
<%@ page import="java.lang.reflect.*" %>
<%@ page import="java.util.*" %>
<%@ page import="org.apache.taglibs.standard.lang.jstl.*" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>

<%
String genPath = pageContext.getServletContext().getRealPath("/generated.jsp");
PrintStream ps = null;
try {
     ps = new PrintStream(new BufferedOutputStream(new 
FileOutputStream(genPath, false), 4096));

     ps.println("<%" + "@ taglib prefix=\"c\" 
uri=\"http://java.sun.com/jstl/core\" %\>");
     ps.println("<html><head>");
     ps.println("<meta http-equiv=\"refresh\" content=\"3; 
URL=elcache.jsp\">");
     ps.println("<title>Generated</title>");
     ps.println("</head><body><ul>");

     long time = System.currentTimeMillis();
     for (int i = 0; i < 100; i++) {
         long value = time + i;
         String var = "v_" + value;
         ps.print("<li>");
         ps.print("<c:set var='" + var + "' value='${" + value + "}'/>");
         ps.print("<c:out value='${pageScope." + var + "}'/>");
         ps.println("</li>");
     }

     ps.println("</ul></body></html>");
} catch (FileNotFoundException exc) {
     exc.printStackTrace();
} finally {
     if (ps != null) {
         ps.close();
     }
}

Field cachedExpressionStringsField = 
ELEvaluator.class.getDeclaredField("sCachedExpressionStrings");
cachedExpressionStringsField.setAccessible(true);
Map cachedExpressionStrings = 
(Map)cachedExpressionStringsField.get(ELEvaluator.class);
%>

<html>

     <head>
         <meta http-equiv="refresh" content="3; URL=generated.jsp">
         <title>EL Cache Test</title>
     </head>

     <body>
         <p>Number cached expr strings: <%= cachedExpressionStrings.size() 
%></p>
     </body>

</html>

It should increase by 200 each time elcache.jsp is accessed. The reason for 
the non-zero refresh is that a newly generated.jsp only seemed to be 
recognized for every request by introducing a slight delay. I ran TC 
4.1.31's Jasper in dev mode so it would check for mods on every request as 
well as setting it not to fork compiles. Of course, JSP compilation could 
still be performed in a background thread within the same JVM, which might 
explain why the delay was required...

Daryl Beattie wrote:
> Yeah, that's basically it! Dunno why I never thought of using a
> scriptlet instead of writing a custom tag... It's probably because
> scriptlets are so frowned-upon where I currently work that I hardly ever
> consider using them.
> 
> One thing I did in one of my tests was actually to print out the size of
> the cache in the JSP. So as my JSP refreshed every second, I could watch
> the size of the cache climb. This, of course, requires a change to
> ELEvaluator.java so that the size of the cache is publicly visible --
> perhaps by adding a "getCacheSize()" method.
> 
> Although I don't like to have my test JSPs actually display their own
> results, the problem with this kind of test is that it can't be easily
> converted to a "unit" test; it's results are somewhat subjective.
> Because of that, I found that adding the cache size to the JSP eased my
> results.
> 
> By adding this to ELEvaluator.java:
> public static int getELCacheSize() {
> 	return ELEvaluator.sCachedExpressionStrings.size();
> }
> 
> You can then change the body of the JSP to:
> <body>
> 	<p>EL Cache Test</p>
> 	<p>EL Cache Size: <%=ELEvaluator.getELCacheSize()%></p>
> </body>
> 
> Then you just load the JSP and watch it climb; if it climbs
> indefinitely, you've got a bug in the cache. If it climbs to a fixed
> size and stops there's no bug. ...And I would personally put the refresh
> delay down to 0 just so that the cache is filled up faster... cuz I'm
> impatient. :)
> 
> - Daryl Beattie
> 
> 
> 
>>-----Original Message-----
>>From: Kris Schneider [mailto:kris@dotech.com] 
>>Sent: Friday, February 25, 2005 1:57 PM
>>To: Tag Libraries Developers List
>>Subject: Re: Memory Leak in ELEvaluator (cont'd...)
>>
>>
>>Here's an approach to dynamically generating unique 
>>expressions that might work as a test.
>>
>>elcache.jsp:
>>------------
>><%@ page import="java.io.*" %>
>><%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>
>>
>><%
>>String genPath = 
>>pageContext.getServletContext().getRealPath("/generated.jsp");
>>PrintStream ps = null;
>>try {
>>    ps = new PrintStream(new BufferedOutputStream(new 
>>FileOutputStream(genPath, false), 4096));
>>
>>    ps.println("<%" + "@ taglib prefix=\"c\" 
>>uri=\"http://java.sun.com/jstl/core\" %\>");
>>    ps.println("<html><head>");
>>    ps.println("<meta http-equiv=\"refresh\" content=\"3; 
>>URL=elcache.jsp\">");
>>    ps.println("<title>Generated</title>");
>>    ps.println("</head><body><ul>");
>>
>>    long time = System.currentTimeMillis();
>>    for (int i = 0; i < 100; i++) {
>>        long value = time + i;
>>        String var = "v_" + value;
>>        ps.print("<li>");
>>        ps.print("<c:set var='" + var + "' value='${" + value 
>>+ "}'/>");
>>        ps.print("<c:out value='${pageScope." + var + "}'/>");
>>        ps.println("</li>");
>>    }
>>
>>    ps.println("</ul></body></html>");
>>} catch (FileNotFoundException exc) {
>>    exc.printStackTrace();
>>} finally {
>>    if (ps != null) {
>>        ps.close();
>>    }
>>}
>>%>
>>
>><html>
>>
>>    <head>
>>        <meta http-equiv="refresh" content="3; URL=generated.jsp">
>>        <title>EL Cache Test</title>
>>    </head>
>>
>>    <body>
>>        <p>EL Cache Test</p>
>>    </body>
>>
>></html>
>>
>>If you drop this into TC's $CATALINA_HOME/webapps/ROOT and 
>>add the JSTL libs to $CATALINA_HOME/webapps/ROOT/WEB-INF/lib, 
>>it should do what you want. I tested this with TC 4.1.31 and 
>>Standard 1.0.6, but didn't do any sort of profiling. If you 
>>don't see the output from generated.jsp change for each 
>>request, try increasing the refresh interval.
>>
>>-- 
>>Kris Schneider <mailto:kris@dotech.com>
>>D.O.Tech       <http://www.dotech.com/>

-- 
Kris Schneider <mailto:kris@dotech.com>
D.O.Tech       <http://www.dotech.com/>

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