wfnet - Embedded work flow engine for Erlang applications

wfnet provides a configuration based workflow enactment engine within an Erlang application.

Historical notes

• This is the second attempt at the same problem.
• The previous attempt was during Spawnfest 2018, however, that was aborted due to other issues not related to the competition.
• No code was committed during the 2018 competion.
• The current effort is a completely new rethink and no code from the 2018 attempt will be used here.

General description

The application will be built in stages, starting with a bare engine, followed by proper OTP based supervised servers, and extended as time permits.

About workflows

Here a workflow is an arrangement of tasks (activities) where each task is only activated when, depending on the task type, one or all of its predecessor(s) have terminated.

The concept, and implementation, of workflows here follows those described on the Workflow patterns web site, more specifically the basic control flow patterns.

Effectively, the workflow is a directed graph of tasks of one of the following types:

wftask: Within wfnet tasks are Erlang functions, either an {Mod, Fun, Args} triple, or a function expression.

• when enabled, the function is called, and the result obtained on completion.
• when terminated, its successor task is enabled.
• A task can only have one predecessor and one successor.

The special tasks are internally defined pseudo-tasks as follows:

• wfenter: this is the first task of the workflow, it has no predecessor. When enabled, it will intialise the workflow data and enable its successor.

• wfexit: this is the last task of the workflow, it has no successors. When enabled, it will clean up and return the data from the workflow

• wfands: this is an AND-split, aka parallel-split, it has a single predecessor, and one or more successors. When enabled, it will enable all its successors.

• wfandj: This is an AND-join, aka synchronization. It will only be enabled when ALL of its predecessors have terminated. When enabled, it will enable its successor.

• wfxors: This is an XOR-split, aka exclusive choice. When enabled, it will enable only one of its successors. The successor is chosen based on the termination result of its predecessor.

• wfxorj: This is an XOR-join, aka simple merge. It has one or more predecessors, and one successor. It is enabled as soon as one of its predecessors terminates.

Build

$ rebar3 compile
$ rebar3 dialyzer

Running with the sample workflows

$ rebar3 shell
> wfnet:start().
> wfnet:load("Examples/sample1.dat").
> wfnet:run_wf().
> wfnet:stop().

The above can also be run with sample2.dat to see the function execution. See the Examples directory for some explanation.

Project status

The development was carried out on a Linux system (archlinux) with Erlang/OTP 26.1.1.

There is much to be done yet:

• Unit tests :-()
• The and-join and xor-split are just dummy place holders.
• We need more realistic examples.

The development will be continued after the Spawnfest weekend, and some rest ;-)

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