TaskScope

Uses thread-local storage to track when a task is executing within a named scope. Other code can query whether it is currently running inside a particular TaskScope<Group>.

Syntax

on<Trigger<T>, TaskScope<Group>>()

Parameters

Parameter	Description
Group	A type tag (typically an empty struct) that identifies this scope.

Behavior

TaskScope implements the scope extension point. When the reaction's callback begins execution, an RAII guard is constructed that marks the scope as active in thread-local storage. When the callback returns (or throws), the guard is destroyed and the scope is deactivated.

• The scope is active only for the duration of the callback.
• Scope state is per-thread — it does not propagate across thread boundaries.
• Multiple TaskScope words with different groups can be active simultaneously.

Example

struct ProcessingScope {};

on<Trigger<Data>, TaskScope<ProcessingScope>>().then([](const Data& d) {
    // TaskScope<ProcessingScope> is active for the duration of this callback
});

Notes

• Useful for conditional behavior based on execution context, such as preventing recursive triggering.
• The Group type follows the same pattern as Sync groups — an empty struct used purely as a type tag.

See Also

• Sync
• Group