JEP 178 - working example?

[Bob Vandette]

My primary goal for implementing JEP 178 was to eliminate any specification barriers in JDK 8 that would prohibit the
implementation of a Java application that might want to link the entire Java runtime into a single application binary.

This allows us to implement the changes that you're suggesting in a JDK 8 implementation without having to 
alter the specification.  This type of spec change is typically only done in major Java releases.

We don't yet have any plans to provide the build system changes that would allow an openjdk build to produce
a complete static library implementation.  It's getting pretty late to push these types of changes into JDK8 as we're pretty
close to feature freeze.

As for use cases for this change, we're trying to enable the creation of single Java application binaries that can take 
advantage of newer compiler technologies such as link time optimization.   This feature coupled with the JDK 8 profiles will allow 
smaller applications that bundle Java binaries to be deployed on app stores.


Bob.


On May 30, 2013, at 6:15 AM, Steve Poole wrote:

> Thanks for the quick response Bob.
> 
> This all seems quite manual - are there any plans to add support to OpenJDK to help with this process?   
> 
> 
> 
> On 29 May 2013, at 00:06, Bob Vandette <bob.vandette at oracle.com> wrote:
> 
>> 
>> 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
>> 
>