78 lines
2.0 KiB
Markdown
78 lines
2.0 KiB
Markdown
---
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title: Cancel, Resume, and Fork Workflows
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impact: MEDIUM
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impactDescription: Control running workflows and recover from failures
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tags: workflow, cancel, resume, fork, control
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---
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## Cancel, Resume, and Fork Workflows
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Use these methods to control workflow execution: stop runaway workflows, retry failed ones, or restart from a specific step.
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**Incorrect (expecting immediate cancellation):**
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```python
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DBOS.cancel_workflow(workflow_id)
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# Wrong: assuming the workflow stopped immediately
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cleanup_resources() # May race with workflow still running its current step
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```
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**Correct (wait for cancellation to complete):**
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```python
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DBOS.cancel_workflow(workflow_id)
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# Cancellation happens at the START of the next step
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# Wait for workflow to actually stop
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handle = DBOS.retrieve_workflow(workflow_id)
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status = handle.get_status()
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while status.status == "PENDING":
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time.sleep(0.5)
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status = handle.get_status()
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# Now safe to clean up
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cleanup_resources()
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```
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### Cancel
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Stop a workflow and remove it from its queue:
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```python
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DBOS.cancel_workflow(workflow_id) # Cancels workflow and all children
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```
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### Resume
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Restart a stopped workflow from its last completed step:
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```python
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# Resume a cancelled or failed workflow
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handle = DBOS.resume_workflow(workflow_id)
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result = handle.get_result()
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# Can also bypass queue for an enqueued workflow
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handle = DBOS.resume_workflow(enqueued_workflow_id)
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```
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### Fork
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Start a new workflow from a specific step of an existing one:
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```python
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# Get steps to find the right starting point
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steps = DBOS.list_workflow_steps(workflow_id)
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for step in steps:
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print(f"Step {step['function_id']}: {step['function_name']}")
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# Fork from step 3 (skips steps 1-2, uses their saved results)
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new_handle = DBOS.fork_workflow(workflow_id, start_step=3)
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# Fork to run on a new application version (useful for patching bugs)
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new_handle = DBOS.fork_workflow(
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workflow_id,
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start_step=3,
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application_version="2.0.0"
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)
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```
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Reference: [Workflow Management](https://docs.dbos.dev/python/tutorials/workflow-management)
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