temporalio/temporal · error

ErrDuplicateRegistration

ErrDuplicateRegistration

Error message

%w: command handler for %v: %v

What it means

Error "%w: command handler for %v: %v" thrown in temporalio/temporal.

Source

Thrown at service/history/workflow/command_handler.go:44

// CommandHandlerRegistry maintains a mapping of command type to [CommandHandler].
type CommandHandlerRegistry struct {
	handlers map[enumspb.CommandType]CommandHandler
}

// NewCommandHandlerRegistry creates a new [CommandHandlerRegistry].
func NewCommandHandlerRegistry() *CommandHandlerRegistry {
	return &CommandHandlerRegistry{
		handlers: make(map[enumspb.CommandType]CommandHandler),
	}
}

// Register registers a [CommandHandler] for a given command type.
// Returns an [ErrDuplicateRegistration] if a handler for the given command is already registered.
// All registration is expected to happen in a single thread on process initialization.
func (r *CommandHandlerRegistry) Register(t enumspb.CommandType, handler CommandHandler) error {
	if existing, ok := r.handlers[t]; ok {
		return fmt.Errorf("%w: command handler for %v: %v", ErrDuplicateRegistration, t, existing)
	}
	r.handlers[t] = handler
	return nil
}

// Handler returns a [CommandHandler] for a given type and a boolean indicating whether it was found.
func (r *CommandHandlerRegistry) Handler(t enumspb.CommandType) (handler CommandHandler, ok bool) {
	handler, ok = r.handlers[t]
	return
}

View on GitHub (pinned to bde624efd1)

When it happens

Trigger: Thrown at service/history/workflow/command_handler.go:44 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of temporalio/temporal@bde624efd1 (2026-09-01). Data as JSON: /api/errors/0fb62cf04838e7a4. Report an issue: GitHub.