Titre :
Les machines virtuelles virtuelles: expérience de la JnJVM (JnJVM is not a JVM)

Auteur : Bertil Folliot (REGAL/RSR/LIP6 - UPMC)

Abstract :

Java runtime became a standard in heterogeneous environments. Indeed,
Java hides the software heterogeneity and facilitates the construction
of applications in an heterogeneous environment. To hide the
heterogeneity of such environment, a Java Virtual Machine hides the
underlying execution environment and provides a clearly defined
interface to interact with the system. Most of the time, this
interface is enough to build an application, but there are some kind
of applications that require particular abstractions, like
persistence, aspect or real time. As Java Virtual Machines are
monolithic, to inject this new behaviors, Java programmers must
develop or modify dedicated Java Virtual Machines and get away from
the specification. Applications developed for these virtual machines
are losing in portability - thus increases the software heterogeneity
- and the code that implements the specialized behavior remains poorly
reusable. Moreover, dynamic code loading prevents an administrator
from knowing which kind of specialized behaviors will be necessary
when the JVM is launched. In this work, we propose to let the
application build itself on the fly its specialized Java Virtual
Machine by modifying an adaptable JVM, called the JnJVM, developed
during this work. The Java application is now portable, because it can
be executed on every JnJVM and the JVM is modified when the
application is loaded and not at the launching time. Our evaluation
shows that the JnJVM is equivalent in performance at HotSpot 1.0, the
first JVM made by SUN Microsystem. To show the interest of our
approach, we have constructed three main specializations of the JnJVM:
an escape analysis runtime, an aspect weaver at the JVM level and a
load balancing system to improve the performance of an application
server.  [Software- Practice and Experience, 38(15):1643-1675, 2008]