Testing hotspot's Atomic::cmpxchg(jbyte*) ?

David Holmes david.holmes at oracle.com
Fri Aug 19 09:26:58 UTC 2016

On 19/08/2016 5:40 PM, Aleksey Shipilev wrote:
> On 08/19/2016 10:13 AM, David Holmes wrote:
>>> Now it might be cleaner to ditch Java version from Unsafe, and make
>>> native entry points like Unsafe_CompareAnd{Exchange,Swap}{Byte,Short}
>>> which would call relevant Atomic::cmpxchg-s.
>> I tried commenting out the Java-ish version and defining one that would
>> call Atomic::cmpxchg from unsafe.cpp in the VM. However something is
>> complaining about the intrinisics - I removed the
>> HotspotIntrinsicCandidate annotation as I don't want any intrinisics,
>> but I get a build error:
>> Compiler intrinsic is defined for method
>> [jdk.internal.misc.Unsafe.compareAndSwapByte(Ljava/lang/Object;JBB)Z],
>> but the method is not annotated with @HotSpotIntrinsicCandidate. Exiting.
>> No idea where this is coming from or how I can disable it ??
> @HotSpotIntrinsicCandidate marks Java methods that are declared in
> vmSymbols.hpp, and the VM code checks it. So, removing @HSIC without
> modifying vmSymbols.hpp would blow up like that.
> Anyway, I think you have to leave @HSIC methods untouched, because C2
> would intrinsify them directly. To cater for the unsafe.cpp slow path,
> do a separate method:
>     @HotSpotIntrinsicCandidate
>     public final byte compareAndExchangeByteVolatile(Object o, long offset,
>                                                      byte expected,
>                                                      byte x) {
>         compareAndExchangeByte0(o, long, expected, x);
>     }
>     public final native byte compareAndExchangeByte0(...);
> ...and then do an entry point for it in unsafe.cpp.

Okay that was the easy part.

Now where do I find out the conditional compilation syntax for the 
X-VarHandle.java.template file?


> Thanks,
> -Aleksey

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