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Volta: Developing Distributed Applications by Recompiling

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Dragos Manolescu, Brian Beckman and Benjamin Livshits, from Microsoft LiveLabs just published an article on Volta, a new technology announced nearly a year ago at the Strategic Architecture Forum 2007. Volta enables the refactoring of an architecture, just like code refactoring tools did for code for over a decade. The why and how of Volta is summarized by the authors as:

Contemporary programming languages and tool suites are designed for quick and easy construction of sequential, nondistributed applications.

To write distributed applications, programmers must learn and use a large variety of lower-level libraries for cross-tier communication, data marshaling, synchronization, and security. The libraries’ sole purpose is to support distributed execution of application logic that could just as well be executed sequentially

[While] most tools and technologies force us to make an a priori partition before writing a single line of code ... [Volta is a set of] tools that, directed by declarative annotations such as RunAt and Async, insert boilerplate code and transform nondistributed executables into logically identical, asynchronous, distributed applications.

Volta works by applying transformation at the CIL (.Net Common Intermediate Language) level which preserve the functional behavior, right before Just-in-Time compilers generate native code. The authors sees several benefits to this approach:

  • the recompiler is language independent
  • the recompiler does not interfere with compiler analyses and optimizations
  • Volta does not need to change when a language specification changes, only when the CIL specification does
  • Volta supports many distributed-design best practices such as "all calls across the network must be asynchronous"
  • Volta provides a many-to-many mapping between the languages in which the code is written and the runtime where the code executes.

It has been speculated that Volta was Microsoft's response to Google's GWT. In the article, the authors are prompt to point out that:

Ajax-style Web-based applications are one of the most popular forms of distributed applications.

and the many-to-many mapping cannot be achieved by GWT because it operates at the code level. Volta provides a CIL-to-JavaScript transformation which can:

simulate advanced control-flow constructs that aren’t natively supported by JavaScript, such as threads and coroutines.

Volta also provides end-to-end instrumentation and profiling capabilities that help understand the effects of partitioning:

The instrumented code can collect complete application traces, enabling us to compute statistics for latency and throughput and to perform application diagnostics.

The authors conclude that Volta:

extends the reach of .NET programming languages, libraries, and tools to cover the cloud.

In the near future, they will focus on on security by construction, finer-grained tier splitting, and tier migration.

Interestingly enough the authors have only detailed so far how to use Volta for Ajax-style Web based application and tier splitting. We can expect that soon they will also apply Volta to help carve and implement "service interactions" in a Service Oriented Architecture helping the refactoring of services and composite services.

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