Lock workflow activity
Summarize
Summary of Lock workflow activity
The Lock workflow activity in ServiceNow ensures that multiple instances of the same workflow do not proceed past a certain point simultaneously. This is particularly useful when workflows trigger multiple times—such as when multiple records are added rapidly—to maintain controlled execution. The lock prevents other workflow instances from continuing until it is explicitly released by the Unlock activity or automatically when the maximum lock duration is reached.
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How the Lock Activity Works
When a workflow instance reaches the Lock activity, it attempts to acquire a lock using a unique key. If another instance holds the lock, the current instance retries acquiring it until the maximum number of attempts is reached. Failure to obtain the lock results in the activity timing out and failing.
It is recommended to precede the Lock activity with a one-second timer activity. This practice helps avoid rare conflicts caused by the lock being associated with the code-execution thread rather than the specific workflow instance.
Important Usage Considerations
- Avoid adding wait-related activities (such as Approval, Task, Timer, Wait for condition, Wait for WF Event, or MID server activities like PowerShell scripts) between Lock and Unlock activities. These can cause the Unlock activity to delay release by up to 60 seconds.
- The lock is temporary and designed to control concurrency without causing workflow delays.
Key Configuration Parameters
- Key: Unique mutex identifier used to acquire and release the lock.
- Max duration: Maximum time the lock is held before auto-release.
- Lock attempts: Defines behavior on lock denial, with the workflow timing out after max attempts.
- Max attempts: Number of retry attempts to obtain the lock.
- Delay between attempts: Wait time between consecutive lock attempts.
Activity States and Results
- Waiting: Workflow is attempting to acquire the lock.
- Finished: Lock was successfully obtained; this instance can proceed while others are blocked.
- Timeout: Lock could not be acquired within the allowed attempts; the activity fails.
The Lock activity prevents other instances of this workflow from continuing past this activity until the lock is released.
Several instances of the same workflow may run concurrently. For example, if a workflow triggers when a record is added to a particular table. That workflow triggers multiple times if multiple records are added one after the other, once by each record insertion. You can use the lock activity to ensure that this instance of the workflow has finished one or more activities before any other instance of the workflow can proceed.
A workflow can explicitly release a lock with the Unlock activity. The lock may also be released when the Max duration is reached.
When an instance of the workflow reaches the Lock activity, it attempts to obtain a lock using the key specified in the lock activity. If another instance has already obtained the lock and has not yet released it, this lock attempt fails. The instance continues trying to obtain the lock until Max attempts has been reached.
We recommend placing a one-second timer activity before the lock activity. This helps prevent a rare condition in which the lock activity may not be able to distinguish one workflow instance from another. This condition can occur because the entity owning the lock is not the specific workflow instance, but rather the code-execution thread in which that instance is running. In most cases, each workflow instance runs on a different thread. Adding a timer activity ensures that this is the case.
- Approval activities
- Task activities
- Timer activities
- Wait for condition activity
- Wait for WF Event activity
- MID server activities such as a PowerShell script
Results
| Result | Description |
|---|---|
| Success | The activity successfully obtained a lock. This instance of the workflow can proceed past this point, but other instances cannot proceed until the lock is released. |
| Failure | After attempting to obtain the lock Max attempts times, the activity could not obtain the lock. |
Input variables
Input variables determine the initial behavior of the activity.
| Field | Description |
|---|---|
| Key | A unique mutex key. The Unlock activity activity uses this key to release the lock. |
| Duration | |
| Max. duration | The maximum time the lock persists. The lock is released after it reaches this duration. Releasing a lock this way is equivalent to running the Unlock activity. |
| Lock attempts Specify how the activity behaves if the lock attempt is denied. If the final lock attempt fails, the activity state is set to 'timeout' and the activity result is set to 'failed'. |
|
| Max. attempts | Specify the maximum number of times the activity may attempt to obtain the lock. |
| Delay between attempts | The amount of time required after a failed lock attempt before another lock attempt is allowed. |
States
The activity state tells the workflow engine what to do with the activity.
| State | Description |
|---|---|
| Waiting | The workflow engine is waiting to obtain a lock. |
| Finished | The activity successfully obtained the lock. |
| Timeout | The activity could not obtain a lock within the number of attempts specified by the Max. attempts input variable. |