Alternatives for Unsafe field access

Nathan Mittler nathanmittler at
Thu Dec 8 20:49:04 UTC 2016

Hi Roger,
If I read that correctly, lookups still have to go through access checks
which would seem to imply that they can't be used for private field access.
Or am I misunderstanding?

On Thu, Dec 8, 2016 at 11:51 AM, Roger Riggs <Roger.Riggs at> wrote:

> Hi Nathan,
> Have you looked at VarHandles?  [1]
> It is possible to use MethodsHandles.Lookup to get a VarHandle to an
> unreflected field.
> Roger
> [1]
> /MethodHandles.Lookup.html
> On 12/8/2016 1:03 PM, Nathan Mittler wrote:
>> Hi everyone,
>> Apologies in advance if this isn't the correct forum for this question. My
>> team is working on an experimental runtime for Google's protocol buffers
>> which is currently relying on sun.misc.Unsafe to perform various tasks
>> efficiently. I'm aware that the plan is to eventually remove Unsafe
>> altogether, and I want to make sure that we still have a way to move
>> forward with future versions of Java.
>> The code is up on a github branch (
>> For an example of the sorts of things our runtime needs to do, you can
>> look
>> at the serialization code (
>> java/core/src/main/java/com/google/protobuf/
>> ).
>> The idea is that the runtime dynamically determines information about
>> message fields (e.g. field types, offsets) and stores it into a single
>> buffer.  Our main need is fast read/write access to the private fields of
>> our generated message classes. Java reflection would be too slow and would
>> require data representation as a list of objects, rather than a continuous
>> buffer (much less compact and cache-friendly). Security restrictions would
>> be a concern as well. At first glance at Java 9, I don't see any
>> facilities
>> that would help here.
>> This would seem to be a fairly common use case a low-level serialization
>> framework, such as protobuf. Are there any thoughts on how such a use case
>> could be supported post-Unsafe?
>> Thanks,
>> Nathan

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