#120 Jacob memory leak

memory (1)
Dima Gurov

Hi guys,
I have a memory leak in Jacob (not Java memory, but JVM process memory) when I'm parsing data returned by Excel (all that data I send from Excel to Java are accumulated in java.exe RAM - I've checked that by memory dump analysis).
I've tried jdk1.6.0_38, jdk1.7.0_51 (64 bit) with the same result.
Also I've followed recommendations from here: http://stackoverflow.com/questions/980483/jacob-doesnt-release-the-objects-properly
with no result.
Here is the way I use Jacob:

final Map<String, T> results = new HashMap<String, T>();
final VariantHolder sourceDataVariantHolder;
if (excelTable != null) {
    sourceDataVariantHolder = excelDispatcher.javaToExcelTable(excelTable);
} else {
    sourceDataVariantHolder = new VariantHolder(null, null, null);
final VariantHolder parametersVariantHolder = parameters.getParametersVariantHolder();
Variant tmp = null;
SafeArray safeArray = null;
    tmp = Dispatch.invoke(
                new Object[] {
                new int[1]);
    safeArray = tmp.toSafeArray();
    final int rows = safeArray.getUBound(1) + 1;
    logger.info("Reading EXCEL String[][] array into a HashMap<String, String>");

    for (int row = 0; row < rows; row++) {
        final String key = safeArray.getString(row, 0);
        final T result = excelDispatcher.excelRowToJava(row, safeArray);
        results.put(key, result);
    if(null != safeArray){
    if(null != tmp){

    // Added this to test Jacob clean-up.
    try {
        logger.info("Let's try to clean-up Jacob...");
        Class<ROT> rot = ROT.class;
        Method clear = rot.getDeclaredMethod("clearObjects", new Class[]{});
        clear.invoke(null, new Object[]{});
        logger.info("Jacob clean-up complete");
    } catch( Exception ex ) {
        logger.error("Problem with Jacob clean-up.");

return results;


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  • Dima, do you run this piece of code only once? Multiple runs should reuse the same memory. Does it work that way?

  • Dima Gurov
    Dima Gurov

    No, I run it repeatedly. Every time all data is accumulated in RAM - I saw 4 copies of my data in memory dump after 4 launches.

  • Please post a full application that exhibits the bug, so that we could try it in our environments. Without that it's hard to tell what's causing the memory growth. You may possibly accumulate the results in other part of your code.

    It would be best to use only WScripting objects or those that can be found on any Windows. But for me Excel is ok.

  • Dima Gurov
    Dima Gurov

    I see... Thanks for your reply.
    During my testing I cleaned up the results just after interaction with Jacob and still saw the leak.
    I will try to extract this part from application, but it's not very easy.

  • I probably got it. Run the code below and notice under task manager that every iteration of k consumes additional 36MB of memory. Is anyone able to fix this code so that it release the memory?

    import com.jacob.activeX.*;
    import com.jacob.com.*;
    public class MemLeak {
      public static void main(String[] args){
        for(int k=1; k<=5; k++) {
          long a = 0;
          for (int j=1; j<20; j++)
          for (int i=1; i<=10000; i++) {
            Variant v = new Variant(3);
            a += v.getInt();
          System.out.println("ready: " + a);
          try { Thread.sleep(5000); } catch (Throwable t){};
          try { Thread.sleep(5000); } catch (Throwable t){};
  • That's weird. After removing Variant.finalize method memory usage reduces several times. And it's not a matter of safeRelease called there, because any finalize method, even as simple as cFin+=1, brings the memory leak back.

    Seems like a Java bug. Could we workaround this? By removing finalize method at all? ComThread.release calls safeRelease anyway. Dima, does this work for you?

  • ... or without jacob modification:

          for (int i=0; i<100; i++) {

    After running ComThread.release(). But this does not reduce the peak memory consumption, which is addressed by total removal of finalize method.

    Recommended reading: Jack Shirazi: The Secret Life Of The Finalizer

  • Dima Gurov
    Dima Gurov

    Thanks for research, I really appreciate it.

    I don't understand what do you mean by 'finalize method' - I do not call it, at least directly.

    Do you mean skipping the whole 'finally' section? Or just "safeArray.safeRelease()" and "tmp.safeRelease()" ?

    • I don't understand what do you mean by 'finalize method' - I do not call it, at least directly.

      You can modify Jacob source as suggested in this comment. If you want to use original Jacob, without modification, use this comment instead. The theory is described in the article, linked from the second comment.

  • Dima Gurov
    Dima Gurov

    Thanks, Jarek.
    Changing the Jacob itself is quite a big task for me, so I've decided to try the second option you've provided.
    I put 1000 cycles instead of 100 just to be on the safe side. Result is negative - the leak is still exist. I've attached memory consumption screenshot (25% CPU usage was for GC 1000 executions).
    NB I set -Xms2048m -Xmx2048m options in my Java, but Java.exe process go beyond that.

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