Fix ConcurrentModificationException while calling emitBufferedMarks in Android

[vivs-nitjsr]

Fix ConcurrentModificationException while calling emitBufferedMarks in Android

Currently, we are getting exception ConcurrentModificationException while calling emitBufferedMarks. The ArrayList is currently iterated and removed in the loop. To fix this iterator can be used, which checks if the element is present in the iterator before processing it. To solve the concurrency on multi threaded environment need to use some concurrent list. Here ConcurrentLinkedQueue can be used to solve the ConcurrentModificationException with the iterator.

[opayen]

I don't think that this will fix the issue. The way iterators work is that they keep a representation of the list's state, and if there is a change made without using this iterator's methods, a ConcurrentModificationException exception is thrown.
Since you use different iterator instances, structural changes will happen from outside, so it will still crash.

Maybe we can use a ConcurrentLinkedQueue instead of an ArrayList?

Otherwise if we still need a List and what we have is write-often - read occasionally, maybe we could use a synchronised copy-on-read collection like this one.

[vivs-nitjsr]

Hi @opayen , I tested it on demo app. I used Iterator with ConcurrentLinkedQueue works perfectly. Iterator with ArrayList was still having the ConcurrentModificationException on multiple threads. I will update the PR with the ConcurrentModificationException.

Demo app that I used is below:

import java.util.Iterator;
import java.util.Queue;
import java.util.Random;
import java.util.concurrent.ConcurrentLinkedQueue;

public class Test {
    
    private static Test instance = null;
    private Queue<String> strs = new ConcurrentLinkedQueue<>();

    private static String [] strings = {"Hello", "How", "are", "you", "doing"};

    public static Test getInstance() {
        if (null == instance) {
            instance = new Test();
        }

        return instance;
    }

    public void addElement(String str) {
        strs.add(str);
    }

    public void removeElement(String str) {
        if(strs.contains(str)) {
            strs.remove(str);
        }
    }

    public static void main (String[] args) {
        for (int j = 0; j < 10; j++) {
            Thread thread = new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0; i < 1000; i++) {
                        int index = new Random().nextInt(strings.length);
                        String s = strings[index];
                        if(i % 2 == 0) {
                            Test.getInstance().addElement(s);
                        } else {
                            Test.getInstance().removeElement(s);
                        }
                        Test.getInstance().printValues();
                    }  
                }
            });
            thread.start();
        }
        
    }

    public void printValues() {
        String p = "";
        Iterator<String> iterator = strs.iterator();
        while (iterator.hasNext()) {
            p += iterator.next() + " ";
        }
    }
}