Workflows

A workflow in sched is a Go function. It runs inside a worker process, and the engine treats it as the durable record of "what should happen and in what order."

The shape of a workflow

client.RegisterWorkflow("MonthlyReport", func(ctx sdk.WorkflowContext, input any) (any, error) {
    ctx.QueueActivity("LoadRows", "users")
    ctx.Sleep(24 * time.Hour)
    ctx.QueueActivity("Mail", "report-ready")
    return "queued", nil
})

ctx exposes the four primitives that distinguish a workflow function from a normal Go function:

QueueActivity(name, input) schedules an activity for execution. The engine records ActivityScheduled in the workflow's history.
Sleep(duration) registers a durable timer with the engine and yields. When the timer fires the engine re-dispatches the workflow task.
WaitForSignal(timeout) yields until an external signal arrives. When SignalWorkflow lands, the engine wakes the workflow.
The function's return value becomes the workflow result and is persisted as WorkflowCompleted.

Replay, not re-execution

Workflow functions are re-run by the engine when something happens to the worker, like a crash. They are not re-executed from scratch; the engine dispatches the workflow's full event history, and the SDK replays the function against that history.

ctx.QueueActivity("LoadRows", "users")   // on replay, skipped (already in history)
ctx.Sleep(24 * time.Hour)                // on replay, yields and waits
ctx.QueueActivity("Mail", "report")      // executes only after the timer fires

This is the same model Temporal and Cadence use. It puts one hard constraint on you:

Workflow functions must be deterministic. Same history in, same commands out. Avoid time.Now(), rand, network calls, and goroutines inside a workflow. Use activities for anything non-deterministic.

Workflow input and output

Inputs and outputs are JSON-encoded on the wire. Use any type that's safe to round-trip through encoding/json:

type ReportRequest struct {
    Month string `json:"month"`
    Region string `json:"region"`
}

client.RegisterWorkflow("MonthlyReport", func(ctx sdk.WorkflowContext, raw any) (any, error) {
    var req ReportRequest
    // The SDK passes input as decoded JSON. Re-marshal if you need a typed struct:
    bytes, _ := json.Marshal(raw)
    if err := json.Unmarshal(bytes, &req); err != nil {
        return nil, err
    }
    // ...
    return req.Month + "-" + req.Region, nil
})

Errors

Returning an error from a workflow marks it as Failed in history. Errors from activities (and how they get retried) live on the activities page.

Cancellation and timeouts