Step decisions

查看 Markdown查看 Markdown

Execute returns a StepDecision. It moves to next Steps, closes the Flow, or both stops this branch and cancels other Steps.

Multiple next Steps

GoTo starts one next Step. GoToMany starts multiple next Steps. Each Step movement has its own input and can also have its own Step options.

Go

12345

return dex.GoToMany(
	dex.MovementOf(carrierAStep{}, Quote{Carrier: "A", Price: 10}),
	dex.MovementOf(carrierBStep{}, Quote{Carrier: "B", Price: 12}),
	dex.MovementOf(winnerStep{}, quote),
), nil

Example: examples/go/primitives/step-decision/workflow.go

Close decisions

Decision	What it does
GracefulComplete	Stops this branch and triggers the Flow to prepare for completion. When all branches and Steps are stopped, the Flow completes.
DeadEnd	Stops this branch only.
ForceComplete	Completes the Flow immediately.
ForceFail	Fails the Flow immediately.

GracefulComplete and ForceComplete can return an output. ForceFail returns a failure reason. The Flow result returns each output with the Step type and Step execution ID. When multiple Steps complete gracefully, all their outputs return together.

A Flow can have no active Steps and still keep running. DeadEnd stops this branch without making a decision that triggers the Flow to complete.

Go

1234567891011

case "graceful":
	return dex.GracefulComplete("done"), nil
case "dead-end":
	return dex.GoToMany(
		dex.MovementOf(branchWorker{}, "left"),
		dex.MovementOf(branchWorker{}, "right"),
	), nil

func (branchWorker) Execute(_ dex.Context, _ string) (*dex.StepDecision, error) {
	return dex.DeadEnd(), nil
}

Example: examples/go/primitives/step-decision/workflow.go

Go

12345678910111213

func (timeoutStep) Execute(
	ctx dex.Context,
	_ dex.None,
) (*dex.StepDecision, error) {
	return dex.ForceFail("Workflow did not finish the task in time"), nil
}

func (taskStep) Execute(
	ctx dex.Context,
	_ bool,
) (*dex.StepDecision, error) {
	return dex.ForceComplete("Workflow completed successfully"), nil
}

Example: examples/go/patterns/timeout/workflow.go

Cancel other Steps

A StepDecision can cancel other active Steps.

• CancelSteps selects active Steps by Step type.
• CancelSiblingSteps selects active Steps that were triggered by the same parent Step execution.

An RPC can also cancel Steps by type. See Cancel running Steps. For how a running attempt observes cancellation, see Cancellation.

Go

1234

func (winnerStep) Execute(_ dex.Context, quote Quote) (*dex.StepDecision, error) {
	return dex.GoTo(recordQuote{}, quote).
		CancelSteps(carrierAStep{}, carrierBStep{}), nil
}

Example: examples/go/primitives/step-decision/workflow.go

ForceCompleteIfChannelsEmpty

ForceCompleteIfChannelsEmpty atomically checks whether all named Channels are empty. A Channel with queued messages is non-empty. After a message is consumed and committed to a Step, that Channel remains non-empty until the Step finishes processing Execute. If every named Channel is empty, it completes the Flow. Otherwise, it goes to other Steps.

Use it to drain Channels and complete the Flow, so the Flow can stay short. See Drain External Channel for the full example.

Go

12345

return dex.ForceCompleteIfChannelsEmpty(
	nil,
	[]dex.ChannelDef{QueueChannel},
	dex.MovementOf(processMessage{}, ""),
), nil

Example: examples/go/patterns/drain-channels/external-publishing/workflow.go