JVMTI developed under JSR-163 and to be released under J2SE 1.5 was designed
as a replacement for JVMPI. The members of the Expert Group felt that one
major release cycle (that is 1.6) was sufficent to convert tools based on JVMPI.
JVMTI is basically an enhanced JVMDI, so JVMDI is no longer needed. To our
knowledge the only products based on JVMDI are Sun's -- the JPDA back-end (which
has already been converted to JVMTI) and jdbx. JVMDI has also been used in
some university research projects.
Maintaining JVMPI and JVMDI in the VM is a significant maintenance burden,
as the VM changes there interfaces break. Their presence complicates the
VM code. And finally, even when off, JVMPI has a performance impact.