RFR: 8003246: Add Supplier to ThreadLocal (original) (raw)

Remi Forax forax at univ-mlv.fr
Thu Dec 6 19:08:52 UTC 2012

On 12/06/2012 08:01 PM, Peter Levart wrote:

There's a quick trick that guarantees in-lining of get/set/remove:

public static class FastThreadLocal extends ThreadLocal { @Override public final T get() { return super.get(); } @Override public final void set(T value) { super.set(value); } @Override public final void remove() { super.remove(); } } ....just use static type FastThreadLocal everywhere in code. I tried it and it works.

No, there is no way to have such guarantee, here, it works either because the only class ThreadLocal you load is FastThreadLocal or because the VM has profiled the callsite see that you only use FastThreadLocal for a specific instruction.

Regards, Peter

cheers, Rémi

On 12/06/2012 01:03 PM, Doug Lea wrote: On 12/06/12 06:56, Vitaly Davidovich wrote:

Doug,

When you see the fast to slow ThreadLocal transition due to class loading invalidating inlined get(), do you not then see it get restored back to fast mode since the receiver type in your call sites is still the monomorphic ThreadLocal (and not the unrelated subclasses)? Just trying to understand what Rémi and you are saying.

The possible outcomes are fairly non-deterministic, depending on hotspot's mood about recompiles, tiered-compile interactions, method size, Amddahl's law interactions, phase of moon, etc. (In j.u.c, we have learned that our users appreciate things being predictably fast enough rather than being unpredictably sometimes even faster but often slower. So when we see such cases, as with ThreadLocal, they get added to todo list.) -Doug

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