COM getStringProperty() memory leak

[sdorof]

I have some COM-server from which I want to get a string property. For this I use COMLateBindingObject#getStringProperty(). It is works, but I have a memory leak.  There is nothing specials, I invoke only getStringProperty(). If I not use this function (just replacing the value by a constant string for the purposes of my program), the leaks disapear. So, is there a bug in JNA? And is there an alternative way to get string property from COM? Is there a some way to free the COM returnted string if the bug on the server side?

Best regards, 

S.D.

[L Will Ahonen]

Hi,

How do you know you have a memory leak, and that it's caused by that exact function?

BR,

Will

[sdorof]

HI

In my application I have a method to get a string from COM-server, like this:

class MyComProxy extends COMLateBindingObject {
  ...
  public String getData() {
    return getStringProperty("my_property");
  }
}

When the application run, the Task Manager shows endless growth in memory until  the COMException "There was not enough memory to complete the operation" followed by OutOfMemory exception. This occurs about 2GB used memory as showed in the Task Manager. In the same time the java's MissionControl shows the used Heap memory less 256MB. 

Next, I change my code to like this:

class MyComProxy extends COMLateBindingObject {
  ...
  public String getData() {
    //return getStringProperty("my_property");
    String data = createRandomDataString();
    return data;
  }
}

In this variant the memory stops growth.

So, I think the problem is in the getStringProperty() function.

пятница, 27 октября 2017 г., 19:55:53 UTC+3 пользователь L Will Ahonen написал:

[Timothy Wall]

What you need to do is change the function signature to return a Pointer, create a String using Pointer.getString(0), and then free the pointer before returning.

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[Matthias Bläsing]

Hey,

Am Freitag, den 27.10.2017, 14:02 -0400 schrieb Timothy Wall:

What you need to do is change the function signature to return a Pointer, create a String using Pointer.getString(0), and then free the pointer before returning.

I disagree. The problem is most probably the handling of Variant in COMLateBindingObject#getStringProperty. Variants that hold strings utilize a BSTR. BSTRs are special in the sense, that they are allocated by SysAllocString and freed by SysFreeString.

For Variants this is handled by VariantClear. VariantClear clears the data contained in the Variant and frees that data (not the Variant itself!).

On Fri, Oct 27, 2017 at 1:20 PM, sdorof <sdo...@gmail.com> wrote:

HI

In my application I have a method to get a string from COM-server, like this:

class MyComProxy extends COMLateBindingObject {

  ...

  public String getData() {

    return getStringProperty("my_property");

  }

}

When the application run, the Task Manager shows endless growth in memory until  the COMException "There was not enough memory to complete the operation" followed by OutOfMemory exception. This occurs about 2GB used memory as showed in the Task Manager. In the same time the java's MissionControl shows the used Heap memory less 256MB. 

Yes this is the implementation of getStringProperty:

    protected String getStringProperty(String propertyName) {

        VARIANT.ByReference result = new VARIANT.ByReference();

        this.oleMethod(OleAuto.DISPATCH_PROPERTYGET, result,

                this.getIDispatch(), propertyName);

        

        return result.stringValue();

    }

So there is no VariantClear call. This would be ok for "basic" variants, that only hold basic values (in this case the value is stored in the autoallocated structure mememory), but not for "complex" types like strings.

@sdorof can you build jna-platform from source and modify the implementation to:

    protected String getStringProperty(String propertyName) {

        VARIANT.ByReference result = new VARIANT.ByReference();

        this.oleMethod(OleAuto.DISPATCH_PROPERTYGET, result,

                this.getIDispatch(), propertyName);

        String res = result.stringValue();

        OleAuto.INSTANCE.VariantClear(result);

        return res;

    }

Thank you

Matthias

[Сергей Дорофеенко]

Hi

пт, 27 окт. 2017, 21:14 Matthias Bläsing <mbla...@doppel-helix.eu>:

Yes, this solve the problem. Thanks.

Sergei D.

Thank you

Matthias

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