Unsafe.{get,put}-X-Unaligned; Efficient array comparison intrinsics

[David Holmes]

On 9/03/2015 9:57 AM, Remi Forax wrote:
>
> On 03/09/2015 12:32 AM, David Holmes wrote:
>> On 9/03/2015 9:21 AM, Remi Forax wrote:
>>>
>>> On 03/09/2015 12:11 AM, David Holmes wrote:
>>>> On 7/03/2015 4:50 AM, Andrew Haley wrote:
>>>>> I've tried to so everything I've been asked.  If this version passes
>>>>> muster with everyone I'll Javadoc all the public methods and fields
>>>>> and put it up for RFA next week.
>>>>>
>>>>> I guess it's going to need a lot of testing and security analysis.
>>>>>
>>>>> I added versions of all {put,get} methods with the boolean bigEndian
>>>>> argument.  This makes HeapByteBuffer much cleaner, and it does not
>>>>> need to know the machine endianness at all.  I hope that's OK.
>>>>>
>>>>> Andrew.
>>>>>
>>>>>
>>>>> http://cr.openjdk.java.net/~aph/unaligned.hotspot.4/
>>>>> http://cr.openjdk.java.net/~aph/unaligned.jdk.4/
>>>>
>>>> I think it is cleaner and more efficient if Unsafe maintains BE as an
>>>> instance variable (initialized at construction) and that isBigEndian()
>>>> simply returns that. The native check should only need to be called
>>>> once in the lifetime of the VM.
>>>>
>>>> David
>>>>
>>>
>>> BE doesn't need to be an instance, method of Unsafe are instance methods
>>> just to enforce security,
>>> you can not call them if you don"t have an instance of Unsafe (and
>>> getUnsafe() does the security check).
>>>
>>> BE is private so it doesn't have to be an instance field it can be
>>> static field.
>>
>> Yes it could but why should it be? You have a singleton instance with
>> all instance methods, so cached state should be in an instance field
>> not a static one.
>
> because the instance of Unsafe is a kind of security token (you get the
> instance once you have pass the security check) and starting to add
> instance field to it will obscure its meaning.

You've completely lost me there. It is an instance therefore it makes 
sense to define everything at the instance level, regardless of why it 
was necessary to define it as an instance in the first place.

David

>>
>>> And I agree with you that the native isBigEndian() should be called once
>>> in the lifetime of the VM.
>>>
>>> so the idea is to write:
>>>
>>> public boolean isBigEndian() {
>>>    return BE;
>>> }
>>> private static final boolean BE = isBigEndian0();
>>>
>>> private static native boolean isBigEndian0();
>>
>> Other than the static parts that is what I was suggesting :)
>>
>> Cheers,
>> David
>
> cheers,
> Rémi
>