potiuk opened a new pull request, #35221:
URL: https://github.com/apache/airflow/pull/35221
Some of the scheduler tests tried to prevent DAG processor processing DAGs
from "tests/dags" directory by setting processor_agent to Mock object:
```python
self.job_runner.processor_agent = mock.MagicMock()
```
This, in connection with scheduler job cleaning all the tables and approach
similar to:
```python
dag = self.dagbag.get_dag("test_retry_handling_job")
dag_task1 = dag.get_task("test_retry_handling_op")
dag.clear()
dag.sync_to_db()
```
Allowed the test to run in isolated space where only one or few DAGS were
present in the DB.
This probably worked perfectly in the past, but after some changes in how
DAGFileProcessor works this did not prevent DAGFileProcessor from running when
_execute method in scheduler_job_runner has been executed, and standalone dag
processor was not running, the processor_agent has been overwritten by a new
DagFileProcessor in the `_execute` method of scheduler_job_runner.
```python
if not self._standalone_dag_processor:
self.processor_agent = DagFileProcessorAgent(
dag_directory=Path(self.subdir),
max_runs=self.num_times_parse_dags,
processor_timeout=processor_timeout,
dag_ids=[],
pickle_dags=pickle_dags,
async_mode=async_mode,
)
```
This led to a very subtle race condition which was more likely on machines
with multiple cores/faster disk (so for example it led to #35204 which appeared
on self-hosted (8 core) runners and did not appear on Public (2-core runners)
or it could appear on an 8 core ARM Mac but not appear on 6 core Intel Mac
(only on sqlite)
If the DAGFileProcessor managed to start and spawn some parsing processes
and grab the DB write access for sqlite and those processes managed to parse
some of the DAG files from tests/dags/ folder, those DAGs could have polutted
the DAGs in the DB - leading to undesired effects (for example with test
hanging while the scheduler job run attempted to process an unwanted subdag and
got deadlocked in case of #35204.
The solution to that is to only set the processor_agent if not set already.
This can only happen in unit tests when the `processor_agent` sets it to Mock
object. For "production" the agent is only set once in the `_execute` methods
so there is no risk involved in checking if it is not set already.
Fixes: #35204
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