sarutak opened a new pull request #7128: [AIRFLOW-6529] Serialization error occurs when the scheduler tries to run on macOS. URL: https://github.com/apache/airflow/pull/7128 When we try to run the scheduler on macOS, we will get a serialization error like as follows. ``` ____________ _____________ ____ |__( )_________ __/__ /________ __ ____ /| |_ /__ ___/_ /_ __ /_ __ \_ | /| / / ___ ___ | / _ / _ __/ _ / / /_/ /_ |/ |/ / _/_/ |_/_/ /_/ /_/ /_/ \____/____/|__/ [2020-01-10 19:54:41,974] {executor_loader.py:59} INFO - Using executor SequentialExecutor [2020-01-10 19:54:41,983] {scheduler_job.py:1462} INFO - Starting the scheduler [2020-01-10 19:54:41,984] {scheduler_job.py:1469} INFO - Processing each file at most -1 times [2020-01-10 19:54:41,984] {scheduler_job.py:1472} INFO - Searching for files in /Users/sarutak/airflow/dags [2020-01-10 19:54:42,025] {scheduler_job.py:1474} INFO - There are 27 files in /Users/sarutak/airflow/dags [2020-01-10 19:54:42,025] {scheduler_job.py:1527} INFO - Resetting orphaned tasks for active dag runs [2020-01-10 19:54:42,059] {scheduler_job.py:1500} ERROR - Exception when executing execute_helper Traceback (most recent call last): File "/Users/sarutak/work/oss/airflow-env/master-python3.8.1/lib/python3.8/site-packages/airflow/jobs/scheduler_job.py", line 1498, in _execute self._execute_helper() File "/Users/sarutak/work/oss/airflow-env/master-python3.8.1/lib/python3.8/site-packages/airflow/jobs/scheduler_job.py", line 1531, in _execute_helper self.processor_agent.start() File "/Users/sarutak/work/oss/airflow-env/master-python3.8.1/lib/python3.8/site-packages/airflow/utils/dag_processing.py", line 348, in start self._process.start() File "/opt/python/3.8.1/lib/python3.8/multiprocessing/process.py", line 121, in start self._popen = self._Popen(self) File "/opt/python/3.8.1/lib/python3.8/multiprocessing/context.py", line 224, in _Popen return _default_context.get_context().Process._Popen(process_obj) File "/opt/python/3.8.1/lib/python3.8/multiprocessing/context.py", line 283, in _Popen return Popen(process_obj) File "/opt/python/3.8.1/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 32, in __init__ super().__init__(process_obj) File "/opt/python/3.8.1/lib/python3.8/multiprocessing/popen_fork.py", line 19, in __init__ self._launch(process_obj) File "/opt/python/3.8.1/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 47, in _launch reduction.dump(process_obj, fp) File "/opt/python/3.8.1/lib/python3.8/multiprocessing/reduction.py", line 60, in dump ForkingPickler(file, protocol).dump(obj) AttributeError: Can't pickle local object 'SchedulerJob._execute.<locals>.processor_factory' ``` The reason is scheduler try to run subprocesses using multiprocessing with spawn mode. Actually, as of Python 3.8, spawn mode is the default mode in macOS. --- Issue link: WILL BE INSERTED BY [boring-cyborg](https://github.com/kaxil/boring-cyborg) - [x] Description above provides context of the change - [x] Commit message/PR title starts with `[AIRFLOW-NNNN]`. AIRFLOW-NNNN = JIRA ID<sup>*</sup> - [x] Unit tests coverage for changes (not needed for documentation changes) - [x] Commits follow "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)" - [x] Relevant documentation is updated including usage instructions. - [x] I will engage committers as explained in [Contribution Workflow Example](https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst#contribution-workflow-example). <sup>*</sup> For document-only changes commit message can start with `[AIRFLOW-XXXX]`. --- In case of fundamental code change, Airflow Improvement Proposal ([AIP](https://cwiki.apache.org/confluence/display/AIRFLOW/Airflow+Improvements+Proposals)) is needed. In case of a new dependency, check compliance with the [ASF 3rd Party License Policy](https://www.apache.org/legal/resolved.html#category-x). In case of backwards incompatible changes please leave a note in [UPDATING.md](https://github.com/apache/airflow/blob/master/UPDATING.md). Read the [Pull Request Guidelines](https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst#pull-request-guidelines) for more information.
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