Module view: Activity UI and Service API


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This view is a module view depicting the key components involved in SB activity execution; that is, requesting an activity described by a Scheduling Block to be run.

Primary Presentation


Major classes responsible for the execution and management of activities.

Element Catalogue

Elements and their properties




ActivityState is an enumeration defining the states that an Activity (a concept linking Scheduling Blocks to Procedures) can be in. State machine for activities has not yet been completely defined and currently Activity can only be in state REQUESTED.


ActivityService provides the high-level API for the activity domain, presenting methods that ‘run a script referenced by activity X of scheduling block Y’. The ActivityService completes user requests by translating the activity requests into Procedure domain commands which then execute the scripts.

The steps taken by the ActivityService to construct a PrepareProcedureCommand are:

  1. retrieve the Scheduling Block by ID from the ODA using the ODA client library

  2. write Scheduling Block to a JSON file as /tmp/sbs/<sb_id>-<version>-<timestamp>.json

  3. convert PDM FileSystemScript object referenced by the given SB and activity to OET FileSystemScript

  4. create a collection of init and run arguments by combining user-defined functions arguments with arguments listed in the SB

  5. add the path to previously written SB JSON file to the run function arguments under key sb_json

  6. create PrepareProcessCommand using the FileSystemScript object and arguments for init function from the collection of function arguments

After the prepare command has been sent, it will wait for a response to record the procedure ID of the script relating to the activity. If prepare_only argument is set to false, ActivityService will create a StartProcessCommand and send it to the ScriptExecutionServiceWorker. It will include the Procedure ID, and request that function named run will be executed with the corresponding arguments.


For a the OET REST deployment, ActivityServiceWorker is the client sending requests to the ActivityService.

ActivityWorker responds to requests received by the FlaskWorker, relaying the request to the ActivityService and publishing the response as an event that can be received by the FlaskWorker and returned to the user in the appropriate format.

Element Interfaces

The major public interface in these interactions is the ActivityService API. For more information on this interface, please see the Module View: REST API.

Element Behaviour

Activity API invocation via HTTP REST

The sequence diagram below illustrates how the components above interact to invoke a call on an remote ActivityService instance in response to a request from a client. This diagram shows how the user request is received by the FlaskWorker REST backend, how that triggers actions on independent ActivityWorker process hosting the ActivityService instance, and how the response is returned to the user


Inter-process publish-subscribe

The Activity domain uses the same publish-subscribe system as Procedure domain for both communication between FlaskWorker and ActivityServiceWorker and for the ActivityService to communicate with the ScriptExecutionServiceWorker. For a diagram illustrating the flow of in-process pypubsub messages, see the Inter-process publish-subscribe section in the script execution API documentation.

Variability Guide



Storing Scheduling Block in the Filesystem

It is currently only possible to deploy the activity and procedure services as one service. This means that the Scheduling Block can be written to file by the ActivityService and it will still be available to the Procedure domain. In the future the Activity and Procedure related services could be deployed in different locations so the current approach of saving SBs to a file should be refactored so that the script running on a different server can also access the SB.

Scheduling Block URI

Currently the Scheduling Block URI used in the OET system is a simple path string to a JSON file referred to by a keyword argument sb_json. In the future this will be expanded into a proper URI with several allowed prefixes such as file:// for SB located in a file and oda:// for SB that should be retrieved from the ODA.