Anand Rajasekar

InheritableThreadLocal and Tomcat

anandsekar — Thu, 08 May 2008 05:18:40 +0000

InheritableThreadLocal does not work with tomcat as tomcat thread pool does not clear the thread local contacts after a request has been executed. This results in no good way to share information information between the parent and the child threads that are created using thread local variables.

One way to solve this problem is to maintain a reference to the parent thread by writing your own thread that is constructed by a thread factory.

public class MyThread extends Thread {
private Thread parent;
public MyThread(Thread parent) {
super();
this.parent = parent;
}
public Thread getParent() {
return parent;
}
}

import java.util.concurrent.ThreadFactory;
public class MyThreadFactory implements ThreadFactory {
@Override
public Thread newThread(Runnable arg0) {
return new MyThread(Thread.currentThread());
}
}

import java.util.HashMap;
import java.util.Map;
public class ClassNeedingInheritableThreadLocal {
private Map inheritableThreadLocal=new HashMap();
public Object getInheritableThreadContext() {
return inheritableThreadLocal.get(getThread());
}
public void setInheritableThreadContext(Object context) {
inheritableThreadLocal.put(getThread(), context);
}
private Thread getThread() {
Thread currentThread=Thread.currentThread();
if(currentThread instanceof MyThread) {
currentThread=getParent((MyThread) currentThread);
}
return currentThread;
}
public Thread getParent(MyThread myThread) {
Thread parent=myThread.getParent();
if(parent instanceof MyThread) {
return getParent((MyThread) parent);
} else {
return parent;
}
}
}

Create a executor service by using our thread factory

ExecutorService service=Executors.newFixedThreadPool(10, new MyThreadFactory());

Remember that you would need to clean up all the objects that were put in the thread local. This can be done with a filter or by using AOP.

நீயே யென் வாழ்கையின் ஆராதனை

anandsekar — Thu, 20 Dec 2007 21:18:40 +0000

நீ பார்த முதல் ஒளி
நான் கேட்டேன் உன் முதல் ஒலி

அரிந்தேன்னே வாழ்கையின் அர்தம்
வியந்தேன்னே வாழ்கையின் அதிசயம்
சூவைத்தேனே வாழ்கையின் அருமை
நீயே யென் வாழ்கையின் ஆராதனை

ஆராதனா

anandsekar — Thu, 20 Dec 2007 20:53:16 +0000

ஆராதனா ..

நீ கண் சிமிட்டும் நிமிடம்
நீ பால் வேண்டாம் எண்று சொன்னா விதம்
எண் மார்பில் தூங்கும் நேரம்
தேங்கும், தேங்கும், மனதில் தேங்கும்

நீ எண் கண் பார்து சிரித்த நிமிடம்
நீ தூங்க மாட்டேன் எண்று அழுதா விதம்
எண் தாலாட்டு பாட்டுக்கு உறங்கும் நேரம்
தேங்கும், தேங்கும், மனதில் தேங்கும்

இப்படிக்கு
ஐய்யா

Finding if Multicast is supported

anandsekar — Tue, 30 Oct 2007 04:09:48 +0000

One way to easily find if mulitcast is supported in a *nix system is to issue

netstat -gn

which returns the membership groups of the mulitcast addresses in the system

e.g. output
Group Memberships: IPv4
Interface Group RefCnt
——— ——————– ——
lo0 224.0.0.75 1
lo0 224.0.0.1 1
eri0 224.0.0.75 1
eri0 224.0.0.1 2

Using Locks for more granular concurrent access

anandsekar — Fri, 21 Sep 2007 21:03:02 +0000

Locks introduced in Java 5 allow a more granular control on a shared resource. When a method is synchronized only the thread that obtains the lock is allowed to enter into that method or any other synchronized method of the class. However some times we may need a more granular control, typically when we have two or more resources we want to share across threads.

e.g.

package org.lock;
public class LockExample {
private boolean initialized;
int salary=0;
public void increaseSalary() {
if(!initialized) {
initialized=true;
salary=1000;
}
salary=salary+100;
}
public void reset() {
initialized=false;
salary=0;
}
}

In this example we need to synchronize access on the initialization and the reset operations. Also we want to make sure that threads have a serialized access when they increase salary.

This is where we can leverage locks. We define two locks, one for initialization and one for the salary operation.

package org.lock;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class LockExample {
Lock initializationLock=new ReentrantLock();
Lock salaryLock=new ReentrantLock();
private boolean initialized;
int salary=0;
public void increaseSalary() {
if(!initialized) {
initializationLock.lock();
try {
initialized=true;
salary=1000;
} finally {
initializationLock.unlock();
}
}
salaryLock.lock();
try {
salary=salary+100;
} finally {
salaryLock.unlock();
}
}
public void reset() {
initializationLock.lock();
try {
initialized=false;
salary=0;
} finally {
initializationLock.unlock();
}
}
}

If you are using Java 1.4 you can utilize temporary synchronization objects to achieve the same result

package org.lock;
public class Lock14Example {
private Object initializationLock=new Object();
private Object salaryLock=new Object();
private boolean initialized;
int salary=0;
public void increaseSalary() {
if(!initialized) {
synchronized(initializationLock) {
initialized=true;
salary=1000;
}
}
synchronized(salaryLock) {
salary=salary+100;
}
}
public void reset() {
synchronized(initializationLock) {
initialized=false;
salary=0;
}
}
}

My First Marathon

anandsekar — Mon, 06 Nov 2006 18:28:35 +0000

I completed the Silicon Valley Marathon on the 29th October in 5 hours and 7 minutes. Its just an amazing feeling. The last 4 miles was particularly remember able, when every step was a huge effort and the crowd cheering you all the way ! Some runners who had completed the marathon walked back with medals around their neck to cheer on. It was so refreshing to see Priya on the final turn, joining along to run the last 200m ! Minutes later I had a medal around my neck !

I had trained for 4 months running 337 miles during my training. Still remember the last two miles when I swore to myself .. â€œNever a marathon againâ€. Two days later, here I am all charged up for my next marathon ! Finally I am a Marathoner !

Joining all lines in a file using sed

anandsekar — Fri, 13 Oct 2006 06:19:19 +0000

Sed (Stream EDitor) is a very powerful stream editor to manipulate text files.
I needed an utility that would join all lines in a text file to a single line with “\n” as a separator so that I could easily cut and paste inline velocity templates into java code. Here is the final sed command !

sed -e :a -e ‘/$/N; s/\n/\\n/; ta’ [filename]

Explanation :

-e - denotes a command to be executed
:a - is a label
/$/N - defines the scope of the match for the current and the (N)ext line
s/\n/\\n/; - replaces all EOL with “\n”
ta; - goto label a if the match is sucessful

Installing Internet Explorer on Linux

anandsekar — Fri, 29 Sep 2006 17:52:19 +0000

The easiest way to install IE in linux is to use IEs4Linux. This is a script that would download all required installables from Microsoft and install IE on your linux system. You need have wine and cabextract preinstalled on the linux box.

Entrust Certification Chain Validation Error using Java Clients

anandsekar — Thu, 31 Aug 2006 17:28:40 +0000

We were stumped yesterday trying to debug why all java clients trying to connect to a secure site using entrust’s Secure Server Certificates were throwing a certificate chain validation error. It turned out that the intermediate certificate that we downloaded from entrust had a bad expiration date. To correct this problem download the intermediate certificate again from entrust (they have posted the correct certificate now !) or remove the intermediate certificate from the server. (http://www.entrust.net/ssl-technical/chaincert_faq.cfm)

Why the Linux file system does not need defragmenting …

anandsekar — Sat, 19 Aug 2006 17:58:37 +0000

I came across this excellant article explaining in simple ways why the linux file system does not need to be defragmented. Read On ..