RFR: 8166187: Regression: NPE during reparse when using persistent code cache and optimistic types

[Attila Szegedi]

Hm… cachedAst is essential for split functions; specifically if it contains a SerializedAst, then its "byte[] serializedAst" field is essential. If cachedAst is lost, we can reparse an unsplit function from source, but we can’t reparse fragments of split functions.

I’d suggest instead of making cachedAst transient, we should:
1. make SerializedAst Serializable, and have SerializedAst.cachedAst within it transient (reference objects aren’t serializable, and we can afford to lose it anyway).
2. introduce RecompilableScriptFunctionData.writeObject and make sure that if serializedAst contains a reference (instead of a SerializedAst object) then we don’t attempt to serialize it — write null instead (this can be accomplished by just setting serializedAst = null, and maybe re-setting it back to what it was after defaultWriteObject)
3. make sure there’s a null check on SerializedAst.cachedAst read in getCachedAst() (as now it can actually be null on deserialization, it was an invariant that it was never null before)

Attila.

> On 22 Dec 2016, at 16:18, Hannes Wallnöfer <hannes.wallnoefer at oracle.com> wrote:
> 
> Please review: 
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8166187
> Webrev: http://cr.openjdk.java.net/~hannesw/8166187/webrev/
> 
> It was actually the combination of having a non-serialisable AST reference and not initialising the transient fields of nested functions that caused this error.
> 
> Thanks,
> Hannes