.
├── cmd/
│   ├── worker/           # Worker process entry point
│   └── starter/          # Workflow starter (client) entry point
├── workflows/            # Workflow definitions
│   ├── order.go
│   └── order_test.go
├── activities/           # Activity definitions
│   ├── payment.go
│   └── payment_test.go
├── shared/               # Shared types (params, results, constants)
│   └── types.go
├── go.mod
└── go.sum

import (
    // Client - for connecting to Temporal and starting workflows
    "go.temporal.io/sdk/client"

    // Workflow - for writing workflow definitions
    "go.temporal.io/sdk/workflow"

    // Activity - for writing activity definitions
    "go.temporal.io/sdk/activity"

    // Worker - for creating and running workers
    "go.temporal.io/sdk/worker"

    // Temporal - for error types and retry policies
    "go.temporal.io/sdk/temporal"

    // Testing - for test environments
    "go.temporal.io/sdk/testsuite"

    // Logging
    "go.temporal.io/sdk/log"
)

package workflows

import (
    "time"
    "go.temporal.io/sdk/workflow"
)

type OrderInput struct {
    OrderID    string
    CustomerID string
    Items      []string
    Amount     float64
}

type OrderResult struct {
    OrderID       string
    PaymentID     string
    TrackingCode  string
    CompletedAt   string
}

func ProcessOrder(ctx workflow.Context, input OrderInput) (*OrderResult, error) {
    logger := workflow.GetLogger(ctx)
    logger.Info("ProcessOrder started", "orderID", input.OrderID)

    // Set activity options (StartToCloseTimeout OR ScheduleToCloseTimeout required)
    ao := workflow.ActivityOptions{
        StartToCloseTimeout: 30 * time.Second,
        RetryPolicy: &temporal.RetryPolicy{
            InitialInterval:    time.Second,
            BackoffCoefficient: 2.0,
            MaximumInterval:    time.Minute,
            MaximumAttempts:    5,
        },
    }
    ctx = workflow.WithActivityOptions(ctx, ao)

    // Use nil struct pointer to call struct-method Activities
    var a *Activities

    var paymentResult PaymentResult
    err := workflow.ExecuteActivity(ctx, a.ChargePayment, input).Get(ctx, &paymentResult)
    if err != nil {
        return nil, err
    }

    var shippingResult ShippingResult
    err = workflow.ExecuteActivity(ctx, a.ShipOrder, input).Get(ctx, &shippingResult)
    if err != nil {
        return nil, err
    }

    return &OrderResult{
        OrderID:      input.OrderID,
        PaymentID:    paymentResult.PaymentID,
        TrackingCode: shippingResult.TrackingCode,
        CompletedAt:  workflow.Now(ctx).Format(time.RFC3339),
    }, nil
}

logger := workflow.GetLogger(ctx)
logger.Info("Processing started", "orderID", orderID)
logger.Error("Activity failed", "Error", err)

encodedRandom := workflow.SideEffect(ctx, func(ctx workflow.Context) interface{} {
    return rand.Intn(100)
})
var randomValue int
encodedRandom.Get(&randomValue)

func SampleTimerWorkflow(ctx workflow.Context, timeout time.Duration) error {
    ao := workflow.ActivityOptions{StartToCloseTimeout: 10 * time.Second}
    ctx = workflow.WithActivityOptions(ctx, ao)

    childCtx, cancelHandler := workflow.WithCancel(ctx)
    selector := workflow.NewSelector(ctx)

    var processingDone bool

    // Add a Future (activity result)
    f := workflow.ExecuteActivity(ctx, OrderProcessingActivity)
    selector.AddFuture(f, func(f workflow.Future) {
        processingDone = true
        cancelHandler() // cancel the timer
    })

    // Add a timer Future
    timerFuture := workflow.NewTimer(childCtx, timeout)
    selector.AddFuture(timerFuture, func(f workflow.Future) {
        if !processingDone {
            _ = workflow.ExecuteActivity(ctx, SendNotificationActivity).Get(ctx, nil)
        }
    })

    // Wait for the first to complete
    selector.Select(ctx)

    // If timer fired first, still wait for processing to finish
    if !processingDone {
        selector.Select(ctx)
    }

    return nil
}

// Simple sleep
workflow.Sleep(ctx, 5*time.Minute)

// Cancellable timer via NewTimer
timerCtx, timerCancel := workflow.WithCancel(ctx)
timer := workflow.NewTimer(timerCtx, 30*time.Minute)

// Cancel the timer when no longer needed
timerCancel()

func SampleGoroutineWorkflow(ctx workflow.Context, parallelism int) ([]string, error) {
    ao := workflow.ActivityOptions{StartToCloseTimeout: 10 * time.Second}
    ctx = workflow.WithActivityOptions(ctx, ao)

    var results []string
    var err error

    for i := 0; i < parallelism; i++ {
        input := fmt.Sprint(i) // capture outside lambda
        workflow.Go(ctx, func(gCtx workflow.Context) {
            // IMPORTANT: use gCtx (the goroutine context), not ctx
            var result string
            err = workflow.ExecuteActivity(gCtx, ProcessItem, input).Get(gCtx, &result)
            if err != nil {
                return
            }
            results = append(results, result)
        })
    }

    // Wait for all goroutines to complete
    _ = workflow.Await(ctx, func() bool {
        return err != nil || len(results) == parallelism
    })
    return results, err
}

// Block indefinitely until condition is met
err := workflow.Await(ctx, func() bool {
    return isApproved
})

// Block with a timeout
ok, err := workflow.AwaitWithTimeout(ctx, 30*time.Second, func() bool {
    return isApproved
})
if err != nil {
    return err // canceled
}
if !ok {
    return temporal.NewApplicationError("approval timed out", "timeout")
}

func ParentWorkflow(ctx workflow.Context) (string, error) {
    cwo := workflow.ChildWorkflowOptions{
        WorkflowID: "child-workflow-id",
        // Optional: TaskQueue, RetryPolicy, etc.
    }
    ctx = workflow.WithChildOptions(ctx, cwo)

    var result string
    err := workflow.ExecuteChildWorkflow(ctx, ChildWorkflow, "input-data").Get(ctx, &result)
    if err != nil {
        return "", err
    }
    return result, nil
}

func ChildWorkflow(ctx workflow.Context, input string) (string, error) {
    logger := workflow.GetLogger(ctx)
    logger.Info("Child workflow started", "input", input)
    return "processed: " + input, nil
}

func LongRunningWorkflow(ctx workflow.Context, state WorkflowState) error {
    // Check if Temporal suggests continuing as new
    if workflow.GetInfo(ctx).GetContinueAsNewSuggested() {
        return workflow.NewContinueAsNewError(ctx, LongRunningWorkflow, state)
    }

    // ... do work, update state ...

    // Explicitly continue as new after N iterations
    state.Iteration++
    if state.Iteration >= 1000 {
        return workflow.NewContinueAsNewError(ctx, LongRunningWorkflow, state)
    }

    return nil
}

err := workflow.Await(ctx, func() bool {
    return workflow.AllHandlersFinished(ctx)
})
if err != nil {
    return err
}
return workflow.NewContinueAsNewError(ctx, MyWorkflow, updatedState)

const ApproveSignal = "approve"

type ApproveInput struct {
    ApproverName string
}

func ApprovalWorkflow(ctx workflow.Context, orderID string) error {
    logger := workflow.GetLogger(ctx)

    // Get the signal channel
    signalChan := workflow.GetSignalChannel(ctx, ApproveSignal)

    // Block until signal is received
    var approval ApproveInput
    signalChan.Receive(ctx, &approval)
    logger.Info("Received approval", "approver", approval.ApproverName)

    // Continue workflow execution after signal...
    return nil
}

func OrderWorkflow(ctx workflow.Context) error {
    var lastSignalData string

    // Listen for signals in a separate goroutine
    workflow.Go(ctx, func(gCtx workflow.Context) {
        signalChan := workflow.GetSignalChannel(gCtx, "my-signal")
        for {
            selector := workflow.NewSelector(gCtx)
            selector.AddReceive(signalChan, func(c workflow.ReceiveChannel, more bool) {
                c.Receive(gCtx, &lastSignalData)
            })
            selector.Select(gCtx)
        }
    })

    // Main workflow logic continues...
    // lastSignalData is updated whenever a signal arrives
    return nil
}

signalChan := workflow.GetSignalChannel(ctx, "my-signal")
for {
    var data string
    ok := signalChan.ReceiveAsync(&data)
    if !ok {
        break
    }
    // process data
}

func QueryableWorkflow(ctx workflow.Context) error {
    currentState := "initialized"

    // Register a query handler
    err := workflow.SetQueryHandler(ctx, "get-state", func() (string, error) {
        return currentState, nil
    })
    if err != nil {
        return err
    }

    // Query handlers with input parameters
    err = workflow.SetQueryHandler(ctx, "get-item", func(itemID string) (*Item, error) {
        item, ok := items[itemID]
        if !ok {
            return nil, fmt.Errorf("item %s not found", itemID)
        }
        return item, nil
    })
    if err != nil {
        return err
    }

    // Workflow logic that updates currentState...
    currentState = "processing"
    workflow.Sleep(ctx, time.Minute)
    currentState = "done"
    return nil
}

const FetchAndAdd = "fetch_and_add"
const Done = "done"

func CounterWorkflow(ctx workflow.Context) (int, error) {
    counter := 0

    // Update handler with validator
    err := workflow.SetUpdateHandlerWithOptions(
        ctx,
        FetchAndAdd,
        func(ctx workflow.Context, addend int) (int, error) {
            previous := counter
            counter += addend
            return previous, nil
        },
        workflow.UpdateHandlerOptions{
            Validator: func(ctx workflow.Context, addend int) error {
                if addend < 0 {
                    return fmt.Errorf("addend must be non-negative (%d)", addend)
                }
                return nil
            },
        },
    )
    if err != nil {
        return 0, err
    }

    // Wait for a "done" signal to finish
    _ = workflow.GetSignalChannel(ctx, Done).Receive(ctx, nil)
    return counter, ctx.Err()
}

type Manager struct {
    state    map[string]string
    nodeLock workflow.Mutex
}

func (m *Manager) AssignNode(ctx workflow.Context, input AssignInput) (AssignResult, error) {
    // Wait until ready
    err := workflow.Await(ctx, func() bool { return m.isStarted })
    if err != nil {
        return AssignResult{}, err
    }

    // Acquire mutex for safe concurrent access
    err = m.nodeLock.Lock(ctx)
    if err != nil {
        return AssignResult{}, err
    }
    defer m.nodeLock.Unlock()

    // Execute activity while holding lock
    actCtx := workflow.WithActivityOptions(ctx, workflow.ActivityOptions{
        ScheduleToCloseTimeout: 10 * time.Second,
    })
    err = workflow.ExecuteActivity(actCtx, DoAssignment, input).Get(actCtx, nil)
    if err != nil {
        return AssignResult{}, err
    }

    m.state[input.NodeID] = input.JobName
    return AssignResult{NodeID: input.NodeID}, nil
}

package activities

import (
    "context"
    "go.temporal.io/sdk/activity"
)

// Simple function activity
func SendEmail(ctx context.Context, recipient, subject, body string) error {
    logger := activity.GetLogger(ctx)
    logger.Info("Sending email", "to", recipient)
    // ... actual email sending logic ...
    return nil
}

type Activities struct {
    DBPool    *pgxpool.Pool
    APIClient *http.Client
    Config    *AppConfig
}

type PaymentInput struct {
    OrderID  string
    Amount   float64
    Currency string
}

type PaymentResult struct {
    PaymentID string
    Status    string
}

func (a *Activities) ChargePayment(ctx context.Context, input PaymentInput) (*PaymentResult, error) {
    logger := activity.GetLogger(ctx)
    logger.Info("Charging payment", "orderID", input.OrderID, "amount", input.Amount)

    // Use shared dependencies
    result, err := a.APIClient.Post(/* ... */)
    if err != nil {
        return nil, err
    }

    return &PaymentResult{
        PaymentID: result.ID,
        Status:    "charged",
    }, nil
}

func (a *Activities) RefundPayment(ctx context.Context, input PaymentInput) error {
    // Compensation activity for saga pattern
    logger := activity.GetLogger(ctx)
    logger.Info("Refunding payment", "orderID", input.OrderID)
    // ... refund logic ...
    return nil
}

// In workflow code:
var a *Activities  // nil pointer is fine -- used only for method resolution
err := workflow.ExecuteActivity(ctx, a.ChargePayment, input).Get(ctx, &result)

func BatchProcessingActivity(ctx context.Context, startIdx, endIdx int) error {
    logger := activity.GetLogger(ctx)

    // Resume from last heartbeat on retry
    i := startIdx
    if activity.HasHeartbeatDetails(ctx) {
        var lastCompleted int
        if err := activity.GetHeartbeatDetails(ctx, &lastCompleted); err == nil {
            i = lastCompleted + 1
            logger.Info("Resuming from heartbeat", "index", i)
        }
    }

    for ; i <= endIdx; i++ {
        // Do work for item i...
        logger.Info("Processing item", "index", i)

        // Record progress -- also delivers cancellation signals
        activity.RecordHeartbeat(ctx, i)

        // Check for cancellation
        select {
        case <-ctx.Done():
            return ctx.Err()
        default:
        }
    }

    return nil
}

ao := workflow.ActivityOptions{
    StartToCloseTimeout: 24 * time.Hour,
    HeartbeatTimeout:    30 * time.Second,  // Must heartbeat at least every 30s
}

import "go.temporal.io/sdk/temporal"

// Retryable error (default) -- will be retried per RetryPolicy
return temporal.NewApplicationError("temporary failure", "TempError", details)

// Non-retryable error -- will NOT be retried regardless of RetryPolicy
return temporal.NewNonRetryableApplicationError("bad input", "ValidationError", nil, details)

// Standard Go errors are converted to retryable ApplicationError automatically
return fmt.Errorf("something went wrong: %w", err)

package main

import (
    "log"

    "go.temporal.io/sdk/client"
    "go.temporal.io/sdk/worker"

    "myapp/activities"
    "myapp/workflows"
)

func main() {
    // Create a Temporal client (heavyweight -- create once per process)
    c, err := client.Dial(client.Options{
        HostPort:  "localhost:7233",       // default
        Namespace: "default",              // default
    })
    if err != nil {
        log.Fatalln("Unable to create client", err)
    }
    defer c.Close()

    // Create a Worker that listens on a specific Task Queue
    w := worker.New(c, "my-task-queue", worker.Options{
        // Optional: tune worker concurrency
        // MaxConcurrentActivityExecutionSize:     defaults to 1000
        // MaxConcurrentWorkflowTaskExecutionSize: defaults to 1000
    })

    // Register Workflow functions
    w.RegisterWorkflow(workflows.ProcessOrder)
    w.RegisterWorkflow(workflows.ApprovalWorkflow)

    // Register Activity struct (registers all exported methods)
    w.RegisterActivity(&activities.Activities{
        DBPool:    dbPool,
        APIClient: httpClient,
        Config:    config,
    })

    // Register standalone Activity functions
    w.RegisterActivity(activities.SendEmail)

    // Run the Worker (blocks until interrupt signal)
    err = w.Run(worker.InterruptCh())
    if err != nil {
        log.Fatalln("Unable to start worker", err)
    }
}