Using Timers :: SAS(R) Workflow Studio 1.3: User's Guide, Second Edition

Overview of Timers

Timers can be used in a workflow to trigger workflow steps at specific times or after specified intervals. Common timer-triggered actions include:

start a task or workflow
stop a task or workflow
automatically traverse a transition
deliver a notification

Defining Timer-Triggered Actions

There are two ways to define timer-triggered actions:

by defining a timer tool. A timer tool enables you to start or stop a task or workflow based on its position in the template. See Adding Timer Tools to a Workflow and Timer Tool Placement and Execution for more information.
by defining a policy that is triggered by a timer. A policy can execute any of the actions described in Policy Actions. To define a policy that starts when a timer fires, define a policy that is triggered by a Timer Expired event. See Policy Events and Timer Expired and Tool Policy Example for more information. Policy-based timers start when the task that contains the timer starts.

Adding Timer Tools to a Workflow

To add a timer to a workflow, click the timer tool

in the toolbar, and then click in the workflow diagram. SAS Workflow Studio automatically adds a Timer Tool policy to the associated task in the workflow tree.

Note: To define a policy that starts when a timer fires, define a policy that is triggered by a Timer Expired event.

Controlling When Timers Start and Stop

Timers start when the task that contains the timer is started or, in the case of stand-alone timers (Outside a Task (Stand-alone Timer Tools)), when the workflow containing the timer is started.

The timer expression that you enter in the Timer Settings dialog box controls when the timer fires (stops). You can enter fire times using Date data objects, relative offsets, or cron expressions. With Date data objects, the fire times can be defined at run time. You can specify both a Date data object and a relative offset. For the Start date firing time, you can specify either a positive or negative offset. For the End date firing time, you can specify positive offsets. See Specifying Timer Settings (Schedule Expressions) for more information.

All outgoing connections from a timer are traversed each time the timer fires.

Timer execution varies depending on its placement in the workflow diagram. See Timer Tool Placement and Execution for more information.

Note: Policy-based timers start when the task that contains the timer starts.

Timer Tool Placement and Execution

Timer Tool on the Border of a Task

A timer tool that is placed on the border of a task stops the task when the timer fires.

In the following example, the timer starts when Task A starts. The timer expression is +60s, which means that the timer is set to fire 60 seconds after it starts.

If Task A completes before the timer fires, then the timer is stopped, and the transition to the Success Stop node is traversed. The workflow instance is stopped with a status of Success.

If Task A has not completed before the timer fires, then Task A is stopped, and the transition to the Timeout Stop node is traversed. The workflow instance is terminated with a status of Timeout.

Workflow showing a timer on the border of task A with a timer expression of +60s. The timer is connected to a stop node with a status of time-out. Task A is also connected to another stop node with a status of success.

Timer Tool inside the Border of a Task

A timer tool that is placed inside the border of a task executes an associated action while the task remains active.

In the following example, the timer starts when Task A starts. The timer expression is +60s, which means that the timer is set to fire 60 seconds after it starts.

Task A triggers Task B 60 seconds after Task A starts. Because the timer is inside the border of Task A, Task A continues to be active after the timer is triggered. Therefore, both Task A and Task B are active after the timer has fired (timer-controlled parallel processing).

workflow showing timer inside task A with a timer expression of +60s. The timer is connected to Task B. Both Task A and Task B are connected to a merge gateway, and the gateway is connected to a stop node with a status of success.

Outside a Task (Stand-alone Timer Tools)

A timer tool that is placed outside a task executes an associated action.

All transitions leading from a stand-alone timer share the same timer interval. You cannot specify different timer intervals for different transitions from the timer. If this behavior is desired, then a separate timer is required for each interval.

In the following example, the timer is placed in the main workflow, so it starts when the workflow instance starts. The timer expression is +60s, which means that the timer is set to fire 60 seconds after it starts.

The timer fires 60 seconds after the workflow instance starts. If Task A has not completed when the timer fires, then the transition to the Timeout Stop node is traversed. The workflow instance to be stopped with a status of Timeout.

If Task A completes before the timer fires, then the timer is stopped, and the transition to the Success Stop node is traversed. The workflow instance is stopped with a status of Success.

workflow diagram that shows a simple process with one task, Task A, that is connected to a stop node with a status of Success. Outside of this task is a time connected to a second stop note with a status of time-out. The timer expression is +60s.

Specifying Timer Settings (Schedule Expressions)

The settings in the Start date section of the Timer Settings dialog box are used to specify the initial time at which the timer fires. The time value can be a Date data object, relative expression, or a cron expression. The End date settings specify when a recurring timer stops firing.

To edit a timer’s settings, double-click on the timer element in the workflow diagram. Alternatively, right-click the Timer Tool policy in the workflow diagram, and select Edit. For policy-based timers, right-click on the policy in the workflow tree, and select Edit.

Note: If the schedule expression has already passed, the timer fires immediately when the associated task or workflow starts.

Timer Setting		Description
Start Date Settings
Date		Specifies a Date data object for initial date and time at which the timer fires. Click to select the data object or to define a new one. You can also specify a relative offset in addition to Date data object. With Date data objects, after the timer has started, changes to the data object do not have any effect. Date data objects are not evaluated until the task or workflow containing the timer has started.
Time value		Specifies a relative time offset for initial time at which the timer fires. The offset is based on when the task that contains the timer starts. Specify the offset with either a plus or minus sign followed by an integer (for example`+30` or `–5`). A negative offset (minus expression) means that the timer fires earlier than the value specified in the Date data object in the Date field. Note: You can enter a negative offset only if you have specified a Date data object.
Time unit		Specifies a time unit for the offset specified in the Time value field. Select Seconds, Minutes, Hours, Days, or Weeks.
Specify cron expression		Specifies a cron expression for initial time at which the timer fires. Relative expressions are based on when the task that contains the timer starts. Cron expressions are especially convenient if you want the timer to expire based on calendar information instead of exact dates or intervals. See the org.quartz.CronExpression documentation at http://quartz-scheduler.org/documentation for information about specifying cron expressions. Note: If you specify a cron expression, all other fields are ignored except for the end date in the Specify date and/or offset field. The syntax for cron expressions implicitly supports repeated firings (recurrence) of the timer object.
This event occurs only one time		Specifies that the timer fires only once.
Recurrence Settings
Recurrence interval		Is a relative expression for the time interval between repeated executions. By default, timers fire only once. Specify an integer (for example `30`).
Time unit		Specifies a time unit for the Recurrence interval. Select Seconds, Minutes, Hours, Days, or Weeks.
End date		Specifies when a recurring timer stops firing.
	No end date	Repeats until the associated task or subflow stops.
	End after	Repeats until the specified the number of occurrences has elapsed.
	Specify date and/or offset	Repeats until the associated date or offset occurs (or both). You can specify a Date data object, a time offset, or both. To specify a date, specify a Date data object in the Date field. Click to select the data object or to define a new one. To specify an offset, specify the offset in the Offset time value field and the time unit in the Time unit field. The offset is based on when the parent element starts. Specify the offset with a plus sign followed by an integer (for example `+30`). Note: You cannot specify negative offsets (minus expressions) for the Offset time value. Note: If you specify a cron expression in the Specify cron expression field, the Offset time value field is ignored.

See Timer Examples for examples of defining timer expressions, including cron syntax.