How to clear my ArrayList is size if 100 in this scenario:

Question

My ultimate goal is to achieve batch processing of lines in an Executor Service. I have the following snippet of code:

while ((bLine = bufferedReader.readLine()) != null) {
    // We will use an array to hold 100 lines, so that we can batch process in a
    // single thread
    batchArray.add(bLine);
    switch (batchArray.size()) {
        case 100:
            Future<?> future = executor.submit(new LocalThreadPoolExecutor(batchArray, closeableHttpClient, httpPost));
            futures.add(future);
           // batchArray.clear() <--- point of failure
            break;
        default:
            logger.info("Batch size in switch: "+batchArray.size());

    }
}

Now if I do an batchArray.clear() in the case 100 I get a concurrentModificationException. Unable to determine how can I reinit the array list and send 100 lines to my executor as they are read from file.

below is the stacktrace:

java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859)
    at java.util.ArrayList$Itr.next(ArrayList.java:831)
    at consumer.ril.com.LocalThreadPoolExecutor.run(LocalThreadPoolExecutor.java:37)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

I get thie exception in my LocalThreadPoolExecutor class when I try to read the batchArray, which is passed in the constructor of this class.

Answer 1

Simple solution -- you need pass to LocalThreadPoolExecutor copy of array and clean original array.

Future<?> future = executor.submit(new LocalThreadPoolExecutor(new ArrayList<>
(batchArray), closeableHttpClient, httpPost));
futures.add(future);
batchArray.clear();