Memory Leak with ByRef Variant

[mkarg]

The following code produces an off-heap memory leak (using JACOB-1.18-M3, also tried JACOB-1.21 on x64 / JVM 17):

String f(int h) {
    var r = new Variant("", true);
    try {
        var c = Dispatch.call(this.dispatch, "f", h, r);
        try {
            c.VariantClear();
        } finally {
            c.safeRelease();
        }
        return r.getStringRef();
    } finally {
        try {
            r.VariantClear();
        } finally {
            r.safeRelease();
        }
   }
}

Running in an infinite loop it easily piles up non-GC-able memory within few minutes! Letting it run endless, java.exe consumes Gigabytes after few hours. Apparently somewhere JACOB is leaking off-heap memory! 🙂

Kindly asking for help! 🙂

[mkarg]

IIUC the problem is caused by the fact that r refers to a Variant of type VT_BSTR | VT_BYREF. As Microsoft says, in that case VariantClear will not clear the BSTR, but leaves this to the caller. The caller is JACOB. The client application has no chance to get the BSTR in its hands to clean it up! Due to that design of JACOB, VT_BSTR | BT_BYREF will always end up in a resource leak.

@freemansoft Can you please confirm this is a design fault of the JACOB API?

Edit: I know that JACOB tries to free the BSTR in release(), but I have no other explanation of the resource leak!