Pass a pointer to JNI_GetCreatedJavaVMs() instead of null (original) (raw)

Alan Bateman Alan.Bateman at oracle.com
Mon May 7 13:27:43 UTC 2012

On 07/05/2012 11:39, David Holmes wrote:

The spec doesn't say anything but the implementation does check for NULL. I think this is a spec issue rather than a code issue (and I think hotspot-runtime owns the JNI spec so cc'ed). It is common practice for API's that take pointers like this to say "if buf is not NULL then the value of XXX is written into buf". Particularly as in this case there will only ever be at most 1 VM created per-process anyway. I'm more concerned about the fact that the code doesn't even check if JNIGetCreatedVMs returns successfully! I agree that the JNI spec needs clarification and it would be inconsistent if this function didn't allow this parameter to be NULL. In addition it would be incompatible change (and would likely break existing code) if the spec were clarified to disallow NULL.

Another point about this JNI function is that it's not clear (to me anyway) how it should behave when there isn't a VM. I think HotSpot currently returns JNI_OK and sets *nVMs to 0 (if non-NULL). Assuming the JNI spec is clarified to specify existing behavior then passing the parameter as NULL just doesn't make sense, meaning JNI_OK does not imply that vmBuf[0] is valid.

-Alan.

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