JNI and JVM TI version numbers

[Alan Bateman]

Has there been any discussion in Project Verona about the native 
interfaces? I don't see anything in JEP 223 on this topic.

In Project Jigsaw / JPMS then we need to update both JNI and the JVM 
Tool Interface for modules. Traditionally then whoever does the first 
update in a major release has the pleasure of rev'ing the version number 
and it looks like we're "it" this time.


The JNI version is currently JNI_VERSION_1_8 (0x00010008). This is the 
version number that GetVersion returns, it's the highest version number 
that can be specified to JNI_CreateJavaVM, and the highest version that 
can be returned by a library's JNI_OnLoad implementation.

Any concerns with moving to JNI_VERSION_9 (0x00090000)? Clearly code 
calling GetVersion and treating the value as a pair of 16-bit values may 
be surprised by a minor version number of 0 but this seems not too 
different to the compatibility issues with changing the values of the 
java.version or java.specification.version properties.

Is rev'ing the JNI version something that JEP 223 should document?


JVM TI is less obvious. Historically it hasn't been tied to the Java SE 
version (I think this was to allow for implementations on J2ME 
profiles). The version number is currently 1.2.3, defined as:

JVMTI_VERSION = 0x30000000 + (1 * 0x10000) + (2 * 0x100) + 3  /* 
version: 1.2.3 */

0x30000000 serves as a base value to separate it from JNI version 
numbers. This is needed because JVM TI environments are obtained via the 
JNI GetEnv function.

JVM TI defines a GetVersion function to return the JVM TI version. It 
also defines shift and mask values to aid extracting the major, minor 
and micro versions. If we moved to 0x30000000 + (9 * 0x10000) then these 
would continue to work, it just might be a surprise to agents that 
expect the major number to be 1 and/or the minor number to be >= some value.

Any thoughts on the JVM TI version? Dropping the major version as 
proposed by JEP 223 seems like the opportunity to do this one time 
change and get the JVM TI version number aligned. On the other hand, 
it's not important and shouldn't be an issue to continue its existing 
version scheme.

-Alan