Because software systems are imperfect, developers are forced to fix bugs
and add new features. The common way of applying changes to a running
system is to stop the application or machine and restart with the new
version. Stopping and restarting causes a disruption in service that is at
best inconvenient and at worst causes revenue loss and compromises safety.
Dynamic software updating (DSU) addresses these problems by updating
programs while they execute. Prior DSU systems for managed languages like
Java and C# lack necessary functionality: they are inefficient and do not
support updates that occur commonly in practice.
This dissertation presents the design and implementation of Jvolve, a DSU
system for Java. Jvolve's combination of flexibility, safety, and
efficiency is a significant advance over prior approaches. Our key
contribution is the extension and integration of existing Virtual Machine
services with safe, flexible, and efficient dynamic updating
functionality. Our approach is flexible enough to support a large class of
updates, guarantees type-safety, and imposes no space or time overheads on
steady-state execution.
Jvolve supports many common updates. Users can add, delete, and change
existing classes. Changes may add or remove fields and methods, replace
existing ones, and change type signatures. Changes may occur at any level
of the class hierarchy. To initialize new fields and update existing ones,
Jvolve applies class and object transformer functions, the former for
static fields and the latter for object instance fields. These features
cover many updates seen in practice. Jvolve supports 20 of 22
updates to three open-source programs---Jetty web server, JavaEmailServer,
and CrossFTP server---based on actual releases occurring over a one to two
year period. This support is substantially more flexible than prior
systems.
Jvolve is safe. It relies on bytecode verification to statically type-check
updated classes. To avoid dynamic type errors due to the timing of an
update, Jvolve stops the executing threads at a DSU safe point and then
applies the update. DSU safe points are a subset of VM safe points, where
it is safe to perform garbage collection and thread scheduling. DSU safe
points further restrict the methods that may be on each thread's stack,
depending on the update. Restricted methods include updated methods for
code consistency and safety, and user-specified methods for semantic
safety. Jvolve installs return barriers and uses on-stack replacement to
speed up reaching a safe point when necessary. While Jvolve does not
guarantee that it will reach a DSU safe point, in our multithreaded
benchmarks it almost always does.
Jvolve includes a tool that automatically generates default object
transformers which initialize new and changed fields to default values and
retain values of unchanged fields in heap objects. If needed, programmers
may customize the default transformers. Jvolve is the first dynamic
updating system to extend the garbage collector to identify and transform
all object instances of updated types. This dissertation introduces the
concept of object-specific state transformers to repair application heap
state for certain classes of bugs that corrupt part of the heap, and a
novel methodology that employes dynamic analysis to automatically generate
these transformers. Jvolve's eager object transformation design and
implementation supports the widest class of updates to date.
Finally, Jvolve is efficient. It imposes no overhead during steady-state
execution. During an update, it imposes overheads to classloading and
garbage collection. After an update, the adaptive compilation system will
incrementally optimize the updated code in its usual fashion. Jvolve is the
first full-featured dynamic updating system that imposes no steady-state
overhead.
In summary, Jvolve is the most-featured, most flexible, safest, and
best-performing dynamic updating system for Java and marks a significant
step towards practical support for dynamic updates in managed language
virtual machines. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2010-05-1436 |
| Date | 26 January 2011 |
| Creators | Subramanian, Suriya |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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