Memory leaks of KeepAliveCache in special circumstances

Question

Hi,
    In a production environment encountered a memory leak problem after running over 200 days, and i found KeepAliveCache.java will produce memory leaks if it create native thread failed.
    I think if keepAliveTimer.start() failed, java.lang.Thread object was not destory and can not collection by GC.
java.security.AccessController.doPrivileged(
   new java.security.PrivilegedAction<Void>() {
   public Void run() {
      // We want to create the Keep-Alive-Timer in the
       // system threadgroup
       ThreadGroup grp = Thread.currentThread().getThreadGroup();
       ThreadGroup parent = null;
       while ((parent = grp.getParent()) != null) {
           grp = parent;
       keepAliveTimer = new Thread(grp, cache, "Keep-Alive-Timer");
       keepAliveTimer.setDaemon(true);
       keepAliveTimer.setPriority(Thread.MAX_PRIORITY - 2);
       // Set the context class loader to null in order to avoid
       // keeping a strong reference to an application classloader.
       keepAliveTimer.setContextClassLoader(null);
       keepAliveTimer.start();
       return null;
we found the top 10 objects used memory are as follows
num     #instances         #bytes  class name
   1:       2287176      256163712  java.lang.Thread
   2:       3200649      197768504  [C
   3:       2378720      190314944  [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry;
   4:        182033       90707352  [Ljava.lang.Object;
   5:       2382405       76236960  java.lang.ThreadLocal$ThreadLocalMap$Entry
   6:       2378720       57089280  java.lang.ThreadLocal$ThreadLocalMap
   7:       2286842       54884208  java.security.AccessControlContext
   8:        212233       28031904  <constMethodKlass>
   9:        902205       21652920  java.lang.String
  10:       2424218       19393744  java.lang.Object
But there are not so many threads in the thread dump, and we found many error log as following:
07:43:21.748  ERROR  WebContainerAdvertiserThread  ?  **.webcontainer.advertiser.startup.WebContainerAdvertiserThread  advertise  WebContainerAdvertiserThread.java  105 
Exception Occured when advertising WebContainer Details
java.lang.OutOfMemoryError: unable to create new native thread
  at java.lang.Thread.start0(Native Method)
  at java.lang.Thread.start(Thread.java:640)
  at sun.net.www.http.KeepAliveCache$1.run(KeepAliveCache.java:89)
  at java.security.AccessController.doPrivileged(Native Method)
  at sun.net.www.http.KeepAliveCache.put(KeepAliveCache.java:75)
  at sun.net.www.http.HttpClient.putInKeepAliveCache(HttpClient.java:370)
  at sun.net.www.http.HttpClient.finished(HttpClient.java:358)
  at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1393)
  at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:379)
Java(TM) SE Runtime Environment (build 1.6.0_25-b06)
SUSE Linux Enterprise Server 10.3
Regards

Answer 1

Hi there..
I'll just answer you what I know..
This code below is when you write your JNI using C++
// this is how to access a java String   
const char *strZ =  env->GetStringUTFChars(
rs( xlzMessage, 0 );
// this is how to let go of java String     
env->ReleaseStringUTFChars( xlzMessage, strZ);     This code below is used when you write your JNI using C
   (*env)->ReleaseStringUTFChars(env, <jstring>,
<char*>);Is this the same as what I have above? If not, what's
the difference?
2. The function has a second jstring argument, ticker,
that is not used (bad style, I know, but I didn't
write the code). Is it necessary to free the memory
for that jstring as well even though I don't use it?If you actually called to GetStringUTFChars successfully, I believed that memory will be allocated and hence, you should call ReleaseUTFChars to deallocate it.
Hope it helps :)