Dispatching Tasks & Workflows From A Workflow

# Dispatching a task

# Sequential processing

Within a workflow, a task can be dispatched from the handle or onEvent generator functions using:

module.exports.handle = function* (...) {
  ...
  const output = yield this.run.task("<task name>", ...<task input>);
  ...
};

When processing the workflow, this instruction means the workflow must stop and process the task <task name> with <task input> data. Once this task is completed by an Agent (and only then), the workflow resumes and set output with the return value of this task.

For example, with:

const a = yield this.run.task("taskA", ...inputA);
const b = yield this.run.task("taskB", ...inputB);            

taskB will be dispatched only after completion of taskA. After completion of taskB, a and b will contain the returned value of taskA and taskB respectively.

# Background processing

If you omit the yieldkeyword:

module.exports.handle = function* (...input) {
  ...
  const job = this.run.task("<task name>", ...<task input>);
  ...
};

The same task will be dispatched, but the workflow will continue processing without waiting for the task completion. So job will be a simple object containing the generated id of the dispatched task:

{
  id: "<uuid>",
}

For example, with:

this.run.task("taskA", ...inputA);
const b = yield this.run.task("taskB", ...inputB);            

taskA and taskB will be dispatched at the same time, but the workflow will only wait for the completion of taskB before continuing.

# Parallel processing

In order to launch multiple tasks in parallel:

const [a, b, c] = yield this.run.task(
    ["taskA", ...inputA],
    ["taskB", ...inputB],
    ["taskC", ...inputC]
);
yield this.run.task("taskD", ...inputD);

Here, taskA, taskB and taskC will be processed in parallel. The workflow will wait for all tasks to complete before dispatching taskD. The output is the array of all returned values.

# Dispatching a child workflow

Within a workflow, a child workflow can be dispatched from the handle or onEvent generator functions using:

module.exports.handle = function* (...) {
  ...
  this.run.workflow("<workflow name>", ...<workflow input>);
  ...
};

The syntax above will dispatch a child workflow in the background: the workflow will continue without waiting for the completion of this child workflow.

If you want to implement a sequential child workflow, look at this workaround.