Support request about FFI Panama Implementation

[Maurizio Cimadamore]

Hi Roberto,
by "singleton limitation" in JNA, I assume you refer to the fact that, 
in JNA (but also JNI) you can only load a native library once, by only 
one classloader. Correct?

If that's the limitation you are trying to workaround, then yes, FFM 
allows you to load the same native library multiple times using its 
SymbolLookup abstraction. Make sure to use the correct factory -- the 
one that does not rely on an association with the current classloader:

https://docs.oracle.com/en/java/javase/23/docs//api/java.base/java/lang/foreign/SymbolLookup.html#libraryLookup(java.lang.String,java.lang.foreign.Arena)

This is just a very thin wrapper around dlopen, so it will take whatever 
library name dlopen can resolve, and will also allow you to open the 
library multiple times. Note that the library will be unloaded when the 
provided arena is closed -- so ideally you could use one arena per client.

Examples of Arena.ofConfined, or custom arenas can be found in the javadoc:

* confined arena - 
https://docs.oracle.com/en/java/javase/23/docs//api/java.base/java/lang/foreign/package-summary.html

* custom arena - 
https://docs.oracle.com/en/java/javase/22/docs//api/java.base/java/lang/foreign/SymbolLookup.html#libraryLookup(java.lang.String,java.lang.foreign.Arena)

We also have some narrative documents on how to use memory segment and 
linker API here:

https://github.com/openjdk/panama-foreign/blob/foreign-memaccess%2Babi/doc/panama_memaccess.md

https://github.com/openjdk/panama-foreign/blob/foreign-memaccess%2Babi/doc/panama_ffi.md

And, if you want to know more on jextract, we have a comprehensive guide 
here:

https://github.com/openjdk/jextract/blob/master/doc/GUIDE.md


Cheers
Maurizio

On 05/02/2025 00:03, roberto.minoletti at trusthub.cloud wrote:
>
> Hello Maurizio,
>
> Thank you to provide the right contact of the Panama project (I 
> reached to you in LinkedIn some days ago)
>
> I am writing to you on behalf of a backend development team that is 
> trying to accomplish our requirements.
>
> We need to interact from our java code (JDK21 that we can easely 
> update to JDK23 if required and Spring Web-Flux) to a C++ library that 
> allow to create Slots, generate Keypairs store Certificates simulating 
> a real HSM (Hardware Security Module). This is named libsofthsm2.so 
> (SoftHSM2).
>
> As I mentioned we customized this library as we need to store 
> certificates and keys in a different path for each user. One important 
> requirement is that we need to be able to process many requests coming 
> from many different users to the same library that should operate in 
> different paths at the same time.
>
> We preliminary resolved a POC using JNA but when tried to execute many 
> parallel treads we faced with his singleton limitation and after a 
> deep reasearch we founded Panama project.
>
> Does Panama FFI support multiple parallel treads? Does it have any 
> Singleton limitations?
>
> What we need is to get many objects/treads at the same time (paralley) 
> loading its own different instance of the same library, getting its 
> own memory context, variables and states, all completely isolated but 
> working at the same time. This was not possible for us because JNA 
> uses the Singleton pattern to load the library directly into the 
> process, making it only possible to have a single instance of the 
> library for the entire process.
>
> The goal is that each object/tread parallely instantiate the same 
> library but having isolated states, configurations and variables 
> stored in a dedicated memory slot for each tread, so even if the C++ 
> library maybe does not completely support cuncurrency itself it should 
> attend multiple treads as it is virtually responding at once having 
> one specific configuration per user.
>
> What we are looking for is that each ARENA has access to 
> libsofthsm2.so and its internal variables using that dedicated memory 
> space to each tread to calculate the operations it must perform.
>
> Does Panama FFI allow all this? This is the first basic question we 
> have. After this we will be able to perform more specific questions.
>
> Also if you have any sample of code that use Arena.ofConfined() or any 
> Custom Arena it would be really fantastic.
>
> Thank you in advance for any information and/or support impelmenting 
> Panama in our Project.
>
> Roberto Minoletti
>
> Trusthub LLC
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/panama-dev/attachments/20250205/5a59ab28/attachment-0001.htm>