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Avoid threads started in contextInitialized() inheriting the AccessCo…
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…ntrolContext and it's ProtectionDomains (at least one of which has the web app classloader) from the current thread. Fixes #23. Also introduce ClassLoaderLeakPreventor.startOracleTimeoutThread setting.
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Mattias Jiderhamn committed Jan 6, 2015
1 parent 856d0fe commit 716b9fb
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Showing 2 changed files with 112 additions and 42 deletions.
9 changes: 9 additions & 0 deletions README.md
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Expand Up @@ -56,6 +56,15 @@ The context listener has a number of settings that can be configured with contex
<td><code>true</code></td>
<td>Should shutdown hooks registered from the application be executed at application shutdown?</td>
</tr>
<tr>
<td><code>ClassLoaderLeakPreventor.startOracleTimeoutThread</td>
<td><code>true</code></td>
<td>
Should the <code>oracle.jdbc.driver.OracleTimeoutPollingThread</code> thread be forced to start with system ClassLoader,
in case Oracle JDBC driver is present? This is normally a good idea, but can be disabled in case the Oracle JDBC
driver is not used even though it is on the classpath.
</td>
</tr>
<tr>
<td><code>ClassLoaderLeakPreventor.threadWaitMs</td>
<td nowrap="nowrap"><code>5000</code><br />(5 seconds)</td>
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145 changes: 103 additions & 42 deletions src/main/java/se/jiderhamn/classloader/leak/prevention/ClassLoaderLeakPreventor.java
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Expand Up @@ -20,21 +20,16 @@
import java.lang.management.RuntimeMXBean;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.*;
import java.net.Authenticator;
import java.net.ProxySelector;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.*;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.*;
import java.util.concurrent.ThreadPoolExecutor;

import javax.management.MBeanServer;
import javax.management.ObjectName;
import javax.servlet.ServletContext;
Expand Down Expand Up @@ -142,6 +137,10 @@ public class ClassLoaderLeakPreventor implements javax.servlet.ServletContextLis
/** Class name for per thread transaction in Caucho Resin transaction manager */
public static final String CAUCHO_TRANSACTION_IMPL = "com.caucho.transaction.TransactionImpl";

private static final ProtectionDomain[] NO_DOMAINS = new ProtectionDomain[0];

private static final AccessControlContext NO_DOMAINS_ACCESS_CONTROL_CONTEXT = new AccessControlContext(NO_DOMAINS);

///////////
// Settings

Expand All @@ -155,6 +154,13 @@ public class ClassLoaderLeakPreventor implements javax.servlet.ServletContextLis
/** Should shutdown hooks registered from the application be executed at application shutdown? */
protected boolean executeShutdownHooks = true;

/**
* Should the {@code oracle.jdbc.driver.OracleTimeoutPollingThread} thread be forced to start with system classloader,
* in case Oracle JDBC driver is present? This is normally a good idea, but can be disabled in case the Oracle JDBC
* driver is not used even though it is on the classpath.
*/
protected boolean startOracleTimeoutThread = true;

/**
* No of milliseconds to wait for threads to finish execution, before stopping them.
*/
Expand Down Expand Up @@ -205,6 +211,7 @@ public void contextInitialized(ServletContextEvent servletContextEvent) {
stopThreads = ! "false".equals(servletContext.getInitParameter("ClassLoaderLeakPreventor.stopThreads"));
stopTimerThreads = ! "false".equals(servletContext.getInitParameter("ClassLoaderLeakPreventor.stopTimerThreads"));
executeShutdownHooks = ! "false".equals(servletContext.getInitParameter("ClassLoaderLeakPreventor.executeShutdownHooks"));
startOracleTimeoutThread = ! "false".equals(servletContext.getInitParameter("ClassLoaderLeakPreventor.startOracleTimeoutThread"));
threadWaitMs = getIntInitParameter(servletContext, "ClassLoaderLeakPreventor.threadWaitMs", THREAD_WAIT_MS_DEFAULT);
shutdownHookWaitMs = getIntInitParameter(servletContext, "ClassLoaderLeakPreventor.shutdownHookWaitMs", SHUTDOWN_HOOK_WAIT_MS_DEFAULT);

Expand All @@ -229,41 +236,94 @@ public void contextInitialized(ServletContextEvent servletContextEvent) {
// Switch to system classloader in before we load/call some JRE stuff that will cause
// the current classloader to be available for garbage collection
Thread.currentThread().setContextClassLoader(ClassLoader.getSystemClassLoader());

initAwt();

initSecurityProviders();

initJdbcDrivers();

initImageIO();

initSecurityPolicy();

initDocumentBuilderFactory();

initDatatypeConverterImpl();

initJavaxSecurityLoginConfiguration();

initJarUrlConnection();

/////////////////////////////////////////////////////
// Load Sun specific classes that may cause leaks

initLdapPoolManager();

initJava2dDisposer();

initSunGC();

initOracleJdbcThread();
// Use doPrivileged() not to perform secured actions, but to avoid threads spawned inheriting the
// AccessControlContext of the current thread, since among the ProtectionDomains there will be one
// (the top one) whose classloader is the web app classloader
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
initAwt();

initSecurityProviders();

initJdbcDrivers();

initImageIO();

initSecurityPolicy();

initDocumentBuilderFactory();

initDatatypeConverterImpl();

initJavaxSecurityLoginConfiguration();

initJarUrlConnection();

/////////////////////////////////////////////////////
// Load Sun specific classes that may cause leaks

initLdapPoolManager();

initJava2dDisposer();

initSunGC();

initOracleJdbcThread();

return null; // Nothing to return
}
}, createAccessControlContext());
}
finally {
// Reset original classloader
Thread.currentThread().setContextClassLoader(contextClassLoader);
}
}

/**
* Create {@link AccessControlContext} that is used in {@link #contextInitialized(javax.servlet.ServletContextEvent)}.
* The motive is to avoid spawned threads from inheriting all the {@link java.security.ProtectionDomain}s of the
* running code, since that will include the web app classloader.
*/
protected AccessControlContext createAccessControlContext() {

final DomainCombiner domainCombiner = new DomainCombiner() {
@Override
public ProtectionDomain[] combine(ProtectionDomain[] currentDomains, ProtectionDomain[] assignedDomains) {
if(assignedDomains != null && assignedDomains.length > 0) {
error("Unexpected assignedDomains - please report to developer of this library!");
}

// Keep all ProtectionDomain not involving the web app classloader
final List<ProtectionDomain> output = new ArrayList<ProtectionDomain>();
for(ProtectionDomain protectionDomain : currentDomains) {
if(protectionDomain.getClassLoader() == null ||
! isWebAppClassLoaderOrChild(protectionDomain.getClassLoader())) {
output.add(protectionDomain);
}
}
return output.toArray(new ProtectionDomain[output.size()]);
}
};

try { // Try the normal way
return new AccessControlContext(NO_DOMAINS_ACCESS_CONTROL_CONTEXT, domainCombiner);
}
catch (SecurityException e) { // createAccessControlContext not granted
try { // Try reflection
Constructor<AccessControlContext> constructor =
AccessControlContext.class.getDeclaredConstructor(ProtectionDomain[].class, DomainCombiner.class);
constructor.setAccessible(true);
return constructor.newInstance(NO_DOMAINS, domainCombiner);
}
catch (Exception e1) {
error("createAccessControlContext not granted and AccessControlContext could not be created via reflection");
return AccessController.getContext();
}
}
}

/**
* Override this method if you want to customize how we determine if we're running in
Expand Down Expand Up @@ -525,18 +585,19 @@ protected void initSunGC() {
}

/**
* To skip this step override this method in a subclass and make that subclass method empty.
*
* See https://github.com/mjiderhamn/classloader-leak-prevention/issues/8
* and https://github.com/mjiderhamn/classloader-leak-prevention/issues/23
* and http://java.jiderhamn.se/2012/02/26/classloader-leaks-v-common-mistakes-and-known-offenders/
*/
protected void initOracleJdbcThread() {
// Cause oracle.jdbc.driver.OracleTimeoutPollingThread to be started with contextClassLoader = system classloader
try {
Class.forName("oracle.jdbc.driver.OracleTimeoutThreadPerVM");
} catch (ClassNotFoundException e) {
// Ignore silently - class not present
if(startOracleTimeoutThread) {
// Cause oracle.jdbc.driver.OracleTimeoutPollingThread to be started with contextClassLoader = system classloader
try {
Class.forName("oracle.jdbc.driver.OracleTimeoutThreadPerVM");
}
catch (ClassNotFoundException e) {
// Ignore silently - class not present
}
}
}

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1 comment on commit 716b9fb

@bradcupit
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Looks good, though I confess I don't understand the code in createAccessControlContext()

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