I'm integrating with an external DLL. One of the functions has a callback:
typedef int (*PROC_DOWNLOAD)(DWORD DataType, DWORD Size, BYTE *pData, DWORD UserDefined);
WORD CALL StartDownload (BYTE CplNum, PROC_DOWNLOAD pfunc, DWORD reserved, DWORD UserDefined);
So the callback passes data, of length SIZE, into pData.
My Callback implementation is as follows:
private static class StartDownloadCallback extends Callback
{
private final UInt32 dataType = DWORD();
private final UInt32 size = DWORD();
private final PrimitiveArray pDataArray = new PrimitiveArray(Int8.class, 0);
private final ExternalArrayPointer pData = new ExternalArrayPointer(pDataArray);
private final UInt32 userDefined = DWORD();
private final Int32 returnValue = INT();
private StartDownloadCallback()
{
init(new Parameter[] {dataType, size, pData, userDefined}, returnValue);
}
public void callback()
{
System.out.println("Callback invoked.");
// extract data
returnValue.setValue(0);
}
}
The first time that it gets called, it receives the correct data (extracted from pData).
However, after that, I get a VM error reported by Windows, with Exception Code c0000005.
Am I taking the correct approach to this? I've looked at the documentation, samples, and forum, and I still wasn't quite sure what to do.
Note that I also tried the same technique as in the sample file CallbackWithFillExternalArraySample.java - i.e. pass in a Pointer.Void instance, and use castTo() on a Pointer to a PrimitiveArray. This had
the same effect as above - worked first time, then failed after that.
Thanks,
Calum
