Attachment 27038 Details for Bug 51195 – Implements the suggested change in StandardHost

[patch] Implements the suggested change in StandardHost

FlushObjectStreamClassCaches.diff (text/plain), 4.46 KB, created by Joern Huxhorn on 2011-05-19 17:19:01 UTC

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Creator: Joern Huxhorn

Created: 2011-05-19 17:19:01 UTC

Size: 4.46 KB

patch

obsolete

>Index: java/org/apache/catalina/core/StandardHost.java
>===================================================================
>--- java/org/apache/catalina/core/StandardHost.java	(Revision 1124979)
>+++ java/org/apache/catalina/core/StandardHost.java	(Arbeitskopie)
>@@ -17,12 +17,15 @@
> package org.apache.catalina.core;
> 
> 
>+import java.lang.reflect.Field;
>+
> import java.util.ArrayList;
> import java.util.List;
> import java.util.Locale;
> import java.util.Map;
> import java.util.WeakHashMap;
> import java.util.regex.Pattern;
>+import java.util.concurrent.ConcurrentHashMap;
> 
> import org.apache.catalina.Container;
> import org.apache.catalina.Context;
>@@ -635,6 +638,8 @@
>      */
>     public String[] findReloadedContextMemoryLeaks() {
>         
>+        preventObjectStreamFalsePositives();
>+        
>         System.gc();
>         
>         List<String> result = new ArrayList<String>();
>@@ -653,6 +658,82 @@
>     }
> 
>     /**
>+     * This method performs additional cleanup to work around the issue described in LBCORE-205 (Logback JIRA)
>+     * and https://issues.apache.org/bugzilla/show_bug.cgi?id=51195
>+     *
>+     * The class java.io.ObjectStreamClass, which is used for serialization, has an internal class Caches
>+     * that keeps SoftReferences to classes previously (de)serialized. This causes a semi-leak since it prevents
>+     * unloading of those classes (and their classloader, including all other loaded classes) until memory is
>+     * running really low, forcing the SoftReferences to be collected by the garbage collection.
>+     *
>+     * This, in turn, causes a leak warning in Tomcat 7 leak-detection.
>+     * One could argue that this is a false positive since the webapp will, at some point, be completely collected.
>+     *
>+     * Regardless of this point, the fix below will, beside fixing the warning, relieve stress from the garbage
>+     * collector, since the amount of memory kept by a webapp classloader can be quite significant.
>+     * Freeing up those resources as soon as possible does make sense in any case.
>+     *
>+     * Calling the method below should be quite safe.
>+     * All relevant exceptions (including SecurityException) are handled properly.
>+     * Clearing the maps in Caches is a safe operation, too, since they are instances of ConcurrentMap and clear()
>+     * is performed atomic. Sudden cleanup of those maps would occur "naturally" in case of low memory, anyway.
>+     *
>+     * The only small "downside" will be a little bit of slowdown in case of further (de)serialization directly
>+     * afterwards since the caches will need to be repopulated.
>+     */
>+    private void preventObjectStreamFalsePositives() {
>+        Throwable t=null;
>+        String className = "java.io.ObjectStreamClass$Caches";
>+        try {
>+            Class clazz = Class.forName(className);
>+            clearStaticConcurrentHashMap(clazz, "localDescs");
>+            clearStaticConcurrentHashMap(clazz, "reflectors");
>+        } catch (ClassNotFoundException e) {
>+            t = e;
>+        } catch (SecurityException e) {
>+            t = e;
>+        }
>+        
>+        if(t != null) {
>+            // ignore
>+            // this would be the right place to add some info that flushing
>+            // did not work out.
>+            // no harm is done, though
>+        }
>+    }
>+    
>+    
>+    private void clearStaticConcurrentHashMap(Class clazz, String fieldName) {
>+        Throwable t=null;
>+        try {
>+            Field field = clazz.getDeclaredField(fieldName);
>+            field.setAccessible(true);
>+            Object value = field.get(null);
>+            if(value instanceof ConcurrentHashMap) {
>+                ConcurrentHashMap map = (ConcurrentHashMap) value;
>+                map.clear();
>+            } else {
>+                // ignore
>+                // this would be the right place to add some info that flushing
>+                // of the field did not work out.
>+                // no harm is done, though
>+            }
>+        } catch (NoSuchFieldException e) {
>+            t = e;
>+        } catch (IllegalAccessException e) {
>+            t = e;
>+        } catch (SecurityException e) {
>+            t = e;
>+        }
>+        if(t != null) {
>+            // ignore
>+            // this would be the right place to add some info that flushing
>+            // of the field did not work out.
>+            // no harm is done, though
>+        }
>+    }
>+
>+    /**
>      * Return the set of alias names for this Host.  If none are defined,
>      * a zero length array is returned.
>      */

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Attachments on bug 51195: 27038 | 29258