Implement no copy memory

[Ardika Rommy Sanjaya]

Hi,

I want to do packet parsing manualy (not using Layout).

>> Wouldn't it make sense for packet parsing to construct a ByteBuffer
>> first, and do the parsing using that?

Yes, I saw that DirectByteBuffer using jdk.internal.misc.Unsafe. But why jdk.internal.misc.Unsafe is not exported in module-info.java? is it because security reason?
Hopefully one day it will exported, because sun.misc.Unsafe is deprecated.

Thanks in advanced

> On 21 May 2019, at 16.40, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
> 
> 
> On 21/05/2019 09:49, Florian Weimer wrote:
>> * Maurizio Cimadamore:
>> 
>>> On 21/05/2019 05:26, Ardika Rommy Sanjaya wrote:
>>>> If using panama should I cast the Pointer<Byte> before get the
>>>> content data?
>>> In Panama you would do this:
>>> 
>>> Pointer<Byte> buf = ...
>>> 
>>> Pointer<Short> ps = buf.cast(NativeTypes.VOID).cast(NativeTypes.UINT16);
>>> short s = ps.get();
>>> 
>>> or...
>>> 
>>> Pointer<Integer> pi = buf.cast(NativeTypes.VOID).cast(NativeTypes.UINT32);
>>> int i = pi.get();
>>> 
>>> Note that you have to cast through VOID first, otherwise the Panama
>>> runtime will complain about incompatible cast.
>> Wouldn't it make sense for packet parsing to construct a ByteBuffer
>> first, and do the parsing using that?
> 
> It really depends on how low-level you want to go. If it's packet parsing what you want to do, it might be possible to describe the layout of the packet you want to parse using a 'Layout' and then you could overlay a custom strcut layout onto the pointer, and then access memory via ordinary getter calls.
> 
> If you want to go the byte-buffer way, there's a way to do that too, using the Pointer::asDirectByteBuffer method.
> 
> http://hg.openjdk.java.net/panama/dev/file/c65ecdbf4155/src/java.base/share/classes/java/foreign/memory/Pointer.java#l217 <http://hg.openjdk.java.net/panama/dev/file/c65ecdbf4155/src/java.base/share/classes/java/foreign/memory/Pointer.java#l217>
> 
> The new memory access-centric API we're working on will also be solid option, moving forward, to read (or write) from native memory - through the VarHandle API [1]. With that API you can build a VarHandle to dereference an address at a given layout element - so if you know the layout of the region you are accessing, you can get a bunch of VarHandle to do the read/write and the JIT will be able to get quite good peak performances (we're currently some 15% behind raw usage of Unsafe, with room to improve).
> 
> [1] - http://cr.openjdk.java.net/~mcimadamore/panama/memaccess.html <http://cr.openjdk.java.net/~mcimadamore/panama/memaccess.html>
> 
>> 
>> Thanks,
>> Florian