RunMonitor

A RunMonitor allows the registration of ICancellable objects, which are cancelled upon cancellation of this monitor. A RunMonitor is associated with every RunContext and IFuture, meaning that executing code can always query its current cancellation status via RunMonitor.CURRENT.get().isCancelled().

A RunMonitor itself is also of the type ICancellable, meaning that it can be registered within another monitor as well. That way, a monitor hierarchy can be created with support of nested cancellation. That is exactly what is done when creating a copy of the current calling context, namely that the new monitor is registered as ICancellable within the monitor of the current calling context. Cancellation only works top-down, and not bottom up, meaning that a parent monitor is not cancelled once a child monitor is cancelled.

When registering a ICancellable and this monitor is already cancelled, the ICancellable is cancelled immediately.

Furthermore, a job’s Future is linked with the job’s RunMonitor, meaning that cancellation requests targeted to the Future are also propagated to the RunMonitor, and vice versa.

The following Figure 1 illustrates the RunMonitor and its associations.