RFR (S) 8031818: Experimental VM flag for enforcing safe object construction (original) (raw)

Aleksey Shipilev aleksey.shipilev at oracle.com
Thu Jan 30 14:14:51 PST 2014

On 01/31/2014 01:53 AM, Vladimir Kozlov wrote:

hs-comp is closed for almost 2 weeks until SQE done all testing. Only ppc merge related fixes are allowed.

Understood, no pressure.

You check isinitializer() for all types of fields in doexits(). But isfinal() is also set for @Stable field which could any methods based on the comment in doputxxx().

Well, that's disturbing.

In pure spec-induced sense, the block emitting the barrier in do_exits() is only valid for initializers. That means, @Stable can indeed mimic its constructor store as the final field store. However, piggybacking on the same code to produce the barrier for an arbitrary method seems very error-prone (and even contradicting the comment in do_exits() which assumes [wrote_final == true] => [method.is_initializer() == true]).

If @Stable writes out the value in an arbitrary method, then it requires release barrier on it's own. It is a pure luck finals also have MemBar_Release, while they could have more relaxed form... especially when/if JMM 9 effort would allow this relaxation. Conflating memory semantics for finals and @Stable seems wrong.

Hence, I think the change is sound. It keeps @Stable semantics for constructor stores. @Stable needs more work to emit release barriers for the arbitrary methods if required (why?), and I think given the failure scenario affects only non-TSO platforms, it can be done separately.

Thoughts? (Vladimir Ivanov, please report in!)

-Aleksey.

Thanks, Vladimir

On 1/30/14 12:15 PM, Aleksey Shipilev wrote: On 01/22/2014 11:13 PM, Aleksey Shipilev wrote:

On 01/22/2014 11:07 PM, Vladimir Kozlov wrote:

Question first: can you wait about 2 weeks when we merge ppc64 changes?

I think we can wait. I don't want to collide with PPC merge either. In fact, it would be even more convenient for us to grab PPC C2 in the experiments from the mainline. Are we open already? I see PPC changes had collided with my patch. Even if it's too early to push the patch, I merged the upstream changes into the updated webrev: http://cr.openjdk.java.net/~shade/8031818/webrev.01/ Instead of introducing a new method, I rewired the predicate and rearranged the comments to make its structure clear. I think extracting method is not required now. Also, a few typos corrected. Testing: - full cycle JPRT -Aleksey.

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