Distributed system simulator and distributed algorithm scratchpad.

• Installation
• dsscratch Model
• Getting Started
• Illustration

So far it includes:

• Processes, Channels, and Topologies
• A TopologyRunner that simulates time and concurrency
• Nodes that can be augmented with modules for encapsulating state and behavior
• A Module template for quickly implementing new modules
  • Modules allow algorithm decoupling. For example, the Two Phase Commit module sends a Broadcast command that will be executed by whatever broadcast component is present.
• Lamport clocks and vector clocks
• Simple broadcast (flooding) and echo algorithms
• Two Phase Commit
• A test module to check whether broadcast algorithms work
• A test module to check whether commit/consensus algorithms work
• The Tarry algorithm for finding a spanning tree of a network
• The Chandy-Lamport snapshot algorithm

Multiple Nodes communicate over FIFO Channels. Each Node encapsulates one or more Modules that represent the logic executed in response to messages (and potentially timers) and encapsulate local state used in that logic.

A Message received at a Node over a Channel is unwrapped and the Command it contains is delivered to each of that Node's Modules. A Module will either execute code after receiving the Command (and potentially send an outgoing Command via its encapsulating Node) or ignore the Command altogether.

For example, Echo.scala defines a simple echo algorithm for broadcasting over the cluster. In its processMessage() method, it looks for one of three Commands: Broadcast, InitiateEcho, or Echo. Any other Commands it ignores.

In order to use dsscratch to implement distributed algorithms, you will implement a Module. You can look at Module.scala for the complete interface (and the ModuleParent interface, which is how a Module communicates with its encapsulating Node). ModuleTemplate.scala provides a template and some guidelines for creating a Module. For a simple example, see SimpleBroadcast.scala.

In order to create a test of your algorithm, you will need to define a separate test Module. For an example of such a test Module, see BroadcastTester.scala, which can be used to test broadcast algorithms.

You run tests via ModuleTest, through which you can define topology parameters as well as test parameters. See SimpleBroadcastTesterRunner.scala for an example.

Fitzroy exploring the treacherous waters of distributed systems theory: