SchedMSG - Description

The schedmsg program provides an interface to interact with the workers, or leaf nodes in DCP. It is able to send message objects to the scheduler, which will then be interpreted and relayed to the worker. The worker can execute tasks if needed and return objects to the scheduler.

Content of Messages

The messages to the schedule are JSON signed with the DCP protocol library which encode JSON having the following properties:

Sample Message

  "type": "broadcast",
  "message": "hello, world",
  "persistent": "true",
  "signature": "ABCBBBDBDBCBCBB#7437274273428BCBCBCB?????",
  "timestamp": "936201600444"


schedmsg.js --type '' --body '' --persistent //don't include persistent for false
schedmsg.js --type broadcast --body 'Hello World' --persistent

Messages between worker and scheduler

Workers routinely communicate with the scheduler to fetch tasks, return result, and perform other tasks. When this happens, the worker will return the timestamp of the last task it worked on. If it is a new worker, the timestamp will be zero. During this time, the timestamp of the worker and the message from schedmsg will be compared to determine if the message should be sent to the worker. There are two cases where the message is considered to be valid:

Broadcast message

If the message type is broadcast and is considered valid, a modal will be displayed on the user’s screen that contains the payload object of the message as the dialogue. The user can hit Cancel, Continue, or X to close the modal. If a modal is being displayed when a new broadcast message is sent, the new message will replace the old one. To avoid duplicate messages, a browser tab will only display a given message once, unless refreshed.

Command message

If the message type if command, the payload property will be treated as a command to be executed by the portal. The user can specify what type of command they want to execute, and provide an extra parameter if necessary. All command messages will be set to persistent : false regardless of the flag set by the user.

Types of Commands

Delete Message

The command schedmsg.js --type delete will simply remove any active modal on the user’s screen. The payload and persistent flag are irrelevant.