1/23/2018 9:18:32 PM
classes for flow trigger feature: TriggerInstance and DependencyInstance.
Conceptually trigger Instance represents an execution of a flow trigger. It holds execution context such as a historically unique trigger execution id, execution status, start/end time, and a list of dependency instances.
Similarly dependency Instance denotes an execution of a dependency performing availability check on a particular data dependency. It holds execution context such as execution status and start/end time, all dependency Instances within the same trigger instance share the same execution id as trigger instance.
A trigger instance and its dependency instances will be created on scheduled trigger start time. The trigger instance will wait until all dependency instances are available, at which point a new flow instance is created, or the maximum allowed wait time is exceeded. Once successfully created, trigger instance will equipped with an UUID to identify itself, initial status as running, and a list of dependency instances whose status are running as well.
Trigger instance can be cancelled manually by user, by timeout when max waiting time is exceeded, or by internal dependency failure.
Trigger/Dependency instance has following status(Running, Cancelling, Cancelled, Succeeded).
Since trigger instance is nothing but a collection of dependency instances, it doesn’t have variables to keep status, start or endtime, all of which can be quickly inferred from its belonging dependencies’ status, start/endtime, which unburdens us from maintaining extra variables.
Cancellation cause will be attached to dependency instance for better user experience when cancelled for whatever reason.
Valid cancellation cause includes:
TIMEOUT, // cancellation is issued due to exceeding max wait time
MANUAL, // cancellation is issued by user
FAILURE, // cancellation is issued by internal dependency instance failure
CASCADING // cancelled by cascading failure(peer dependency is cancelled)
