JEP 178 - working example?

[Bob Vandette]

On May 28, 2013, at 7:06 AM, Steve Poole wrote:

> 
> hi everyone,  
> 
> I've been reading JEP 178  (Statically-Linked JNI Libraries )  http://openjdk.java.net/jeps/178
> 
> There is a sentence  in the  section on JNI Specification changes that says
> 
> "A native library may be statically linked with the VM. The manner in which the library and VM image are combined is implementation-dependent."
> 
> I can't find anything that explains the process  in more detail so posting here.
> 
> Basically - if I want to statically link my JNI library to Hotspot what are the instructions for the OpenJDK implementation?  

Since the procedure for statically linking binaries into a executable is very platform specific, the specification 
intentionally leaves out these details.

The key functional changes that were implemented to support this spec change, were:

1. Require JNI_OnLoad_{libraryname} for static libraries.
2. Modify the Java API's that load native JNI libraries to support static libraries by detecting the
presence of the library specific OnLoad function.
3. Support JNI_OnUnLoad_{libraryname}

So you can either build the entire JDK as static libraries, change every JNI_OnLoad function to be 
unique and link them all together with a java launcher.

OR

You can create a single static library, making sure to give it a unique JNI_OnLoad_{libraryname}
entrypoint, link it with a program executable that loads the VM via the Java launcher or Invocation APIs.

For example:  If your library name is speciallibrary.a, you would then call System.loadLibrary("speciallibrary")

Once the loadLibrary call succeeds, you can then call any native Java methods defined by the static library.

Bob.


> 
> 
> Cheers
> 
> Steve