I used synchronized list, and i still get ConcurrentModificationException

java multithreading vector synchronized
Shelef picture Shelef · Mar 15, 2013 · Viewed 7k times · Source

I'm using Vector instead of ArrayList to make a list safe in multi-threaded enviroment. But I keep getting ConcurrentModificationException when I trying to add items to the Vector while iterating it. Why is that and how can I prevent it?

Answer

fredrik picture fredrik · Mar 15, 2013

You cannot modify a Vector while iterating over it. Store the items to add in a separate vector, and move them to the Vector when the loop is finished or loop over a copy of the original Vector.

ADDED: To get a mutex around the Vector in java, do this in both functions:

synchronized (list) {
  // modifying list
}

and:

synchronized (list) {
  // iterating over list
}

Of course I've assumed that the list is named list

Related questions

Difference between wait() and sleep()

What is the difference between a wait() and sleep() in Threads? Is my understanding that a wait()-ing Thread is still in running mode and uses CPU cycles but a sleep()-ing does not consume any CPU cycles correct? Why …

Read More
"implements Runnable" vs "extends Thread" in Java

From what time I've spent with threads in Java, I've found these two ways to write threads: With implements Runnable: public class MyRunnable implements Runnable { public void run() { //Code } } //Started with a "new Thread(new MyRunnable()).start()" call Or, with …

Read More
How to properly stop the Thread in Java?

I need a solution to properly stop the thread in Java. I have IndexProcessorclass which implements the Runnable interface: public class IndexProcessor implements Runnable { private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class); @Override public void run() { boolean run = true; …

Read More