Java Implementation of Flow-Based Programming (FBP)

In computer programming, flow-based programming (FBP) is a programming paradigm that defines applications as networks of "black box" processes, which exchange data across predefined connections by message passing, where the connections are specified externally to the processes. These black box processes can be reconnected endlessly to form different applications without having to be changed internally. FBP is thus naturally component-oriented.

FBP is a particular form of dataflow programming based on bounded buffers, information packets with defined lifetimes, named ports, and separate definition of connections.

Web sites for FBP:

• http://www.jpaulmorrison.com/fbp/
• https://github.com/flowbased/flowbased.org/wiki

The project requires Gradle for building (tested with version 2.0). You can download the corresponding package from the following URL: http://www.gradle.org

Windows and Linux users should follow the installation instructions on the Maven website (URL provided above).

OSX users (using Brew, http://brew.sh) can install Maven by executing the following command:

brew install gradle

You can generate Eclipse project using the following mvn command:

gradle eclipse

If you already created an Eclipse project you can run:

gradle cleanEclipse Eclipse

You need to install a Gradle plugin for Eclipse as explain here: https://github.com/spring-projects/eclipse-integration-gradle/ Then import a generated project in Eclipse, right (ctrl for OSX) click on the project in Eclipse -> Configure -> Convert to Gradle Project. After the conversion you can Right (ctrl for OSX) click on the project -> Gradle -> Task Quick Launcher and type build.

For building the project simply run the following command:

gradle build

As a result a javafbp-2.9.jar file will be created in the build/libs directory. It will include the JavaFBP core (runtime) and all the examples from the source code (sub-package com.jpmorrsn.fbp.examples).

For running any of the examples use the following command:

java -cp build/libs/javafbp-2.9.jar com.jpmorrsn.fbp.examples.networks.<Class name of the network>

For example:

java -cp build/libs/javafbp-2.9.jar com.jpmorrsn.fbp.examples.networks.TestIPCounting

Here is a simple test that can be run to test that everything is working.

In the project directory, enter

java -cp build/libs/javafbp-2.9.jar com.jpmorrsn.fbp.examples.networks.MergeandSort

Here is a picture of MergeandSort, drawn using DrawFBP:

This network contains 4 processes:

• 2 occurrences of GenerateTestData,
• a Sort process - a very simple-minded Sort, which can only handle up to 9,999 information packets
• a text display component, which invokes Java Swing to display the sorted data in a scroll pane.

The outputs of the two GenerateTestData processes are merged on a "first come, first served" basis. During the run you should see a scroll pane with the sorted data scrolling down.

At the end of the run, you should see:

Run complete.  Time: x.xxx seconds
Counts: C: 150, D: 153, S: 300, R (non-null): 304, DO: 0

where the counts are respectively: creates, normal drops, sends, non-null receives, and drops done by "drop oldest".

This uses an additional jar file: Java-WebSocket-1.3.1.jar, see TooTallNate/Java-WebSocket#118. As this has not yet been released to the central Maven repository, we have to include and distribute the required jar in a local lib directory, which of course impacts publication of our own jar into the central Maven repository.

You can however run the test server code in com.jpmorrsn.fbp.websockets.networks.TestWebSockets by entering in the project directory

java -cp "build\libs\javafbp-2.9.jar;lib\Java-WebSocket-1.3.1.jar" com.jpmorrsn.fbp.websockets.networks.TestWebSockets

(note the double quotes).

There is a very simple client script called chat1 in com/jpmorrsn/fbp/websockets/script: open it with web browser while server is running; enter namelist in input field; click on send. You should see 3 names after a random delay. Click on Stop WS to bring down the server. An identical script has also been provided called chat2 to allow testing of multiple clients.

If running this test under Eclipse, you can add Java-WebSocket-1.3.1.jar to Run/Debug Settings/Launch Configuration for TestWebSockets.

To trace JavaFBP services and/or lock usage, set the appropriate parameter(s) in JavaFBPProperties.xml in the user directory to true:

• tracing
• tracelocks

These traces will appear in the project directory under the name xxxx-fulltrace.txt, where xxxx is the name of the network being run. Subnets have their own trace output files.

Two other options are also supported in the properties file:

• deadlocktest (defaults to true, so you might set it to false if debugging)
• forceconsole (used if immediate console output is required during debugging - normally, console output is sent to a file)