[9] RFR (XS): 8151623: Zap freed Metaspace chunks in non-product binaries

[Vladimir Ivanov]

> I thought there was a Zap flag for metadata, but maybe not.  I don't
> know if it's worth the trouble to add a new flag.
There are many Zap* flags, but ZapMetadata is not among them:

develop(bool, ZapResourceArea, trueInDebug,
       "Zap freed resource/arena space with 0xABABABAB")

notproduct(bool, ZapVMHandleArea, trueInDebug,
       "Zap freed VM handle space with 0xBCBCBCBC")

develop(bool, ZapJNIHandleArea, trueInDebug,
       "Zap freed JNI handle space with 0xFEFEFEFE")

notproduct(bool, ZapStackSegments, trueInDebug,
       "Zap allocated/freed stack segments with 0xFADFADED")

develop(bool, ZapUnusedHeapArea, trueInDebug,
       "Zap unused heap space with 0xBAADBABE")

develop(bool, ZapFillerObjects, trueInDebug,
       "Zap filler objects with 0xDEAFBABE")

I don't have a strong opinion here. The usefulness of these flags looks 
questionable, considering: (1) zapping is turned on by default in debug 
builds and (2) there is not way to turn it on in product.

They can be switched on in optimized build, but it is not that popular 
these days.

Best regards,
Vladimir Ivanov