Also store success boolean to pickle output when using multiprocessing (

#686)

* also store success boolean to pickle output when using multiprocessing instead of slurm

* update changelog

* merge print and logging instructions; convert print to logging in other places, too

* add logging import

* fix return value propagation in multiprocessing context with serialization of result

* format

cluster_tools/Changelog.md

@@ -10,6 +10,7 @@ For upgrade instructions, please check the respective *Breaking Changes* section
 [Commits](https://github.com/scalableminds/webknossos-libs/compare/v0.9.17...HEAD)
 
 ### Breaking Changes
+- The cluster-tools serialize the output of a job in the format `(wasSuccessful, result_value)` to a pickle file if `output_pickle_path` is provided and multiprocessing is used. This is consistent with how it is already done when using a cluster executor (e.g., slurm). [#686](https://github.com/scalableminds/webknossos-libs/pull/686)
 
 ### Added
 

cluster_tools/cluster_tools/__init__.py

@@ -1,3 +1,4 @@
+import logging
 import multiprocessing
 import os
 import tempfile
@@ -161,12 +162,19 @@ def _execute_and_persist_function(output_pickle_path, *args, **kwargs):
         func = args[0]
         args = args[1:]
 
-        result = func(*args, **kwargs)
+        try:
+            result = True, func(*args, **kwargs)
+        except Exception as exc:
+            result = False, exc
+            logging.warning(f"Job computation failed with:\n{exc.__repr__()}")
 
         with open(output_pickle_path, "wb") as file:
             pickling.dump(result, file)
 
-        return result
+        if result[0]:
+            return result[1]
+        else:
+            raise result[1]
 
     def map_unordered(self, func, args):
 

cluster_tools/cluster_tools/remote.py

@@ -47,8 +47,7 @@ def worker(executor, workerid, job_array_index, job_array_index_offset, cfut_dir
 
     try:
         input_file_name = executor.format_infile_name(cfut_dir, workerid_with_idx)
-        print("trying to read: ", input_file_name)
-        print("working dir: ", os.getcwd())
+        logging.debug(f"Trying to read: {input_file_name} (working dir: {os.getcwd()}")
 
         custom_main_path = get_custom_main_path(workerid, executor)
         with open(input_file_name, "rb") as f:
@@ -78,10 +77,9 @@ def worker(executor, workerid, job_array_index, job_array_index_offset, cfut_dir
         out = pickling.dumps(result)
 
     except Exception:
-        print(traceback.format_exc())
 
         result = False, format_remote_exc()
-        logging.warning("Job computation failed.")
+        logging.warning(f"Job computation failed with:\n\n{traceback.format_exc()}")
         out = pickling.dumps(result)
 
     # The .preliminary postfix is added since the output can

cluster_tools/cluster_tools/schedulers/cluster_executor.py

@@ -103,7 +103,7 @@ def executor_key(cls):
     def handle_kill(self, _signum, _frame):
         self.wait_thread.stop()
         job_ids = ",".join(str(id) for id in self.jobs.keys())
-        print(
+        logging.debug(
             "A termination signal was registered. The following jobs are still running on the cluster:\n{}".format(
                 job_ids
             )
@@ -204,7 +204,7 @@ def _completion(self, jobid, failed_early):
             if not self.jobs:
                 self.jobs_empty_cond.notify_all()
         if self.debug:
-            print("job completed: {}".format(jobid), file=sys.stderr)
+            logging.debug("Job completed: {}".format(jobid), file=sys.stderr)
 
         preliminary_outfile_name = with_preliminary_postfix(outfile_name)
         if failed_early:
@@ -298,7 +298,7 @@ def submit(self, fun, *args, **kwargs):
         jobid = jobids_futures[0].result()
 
         if self.debug:
-            print(f"job submitted: {jobid}", file=sys.stderr)
+            logging.debug(f"Job submitted: {jobid}", file=sys.stderr)
 
         # Thread will wait for it to finish.
         self.wait_thread.waitFor(preliminary_output_pickle_path, jobid)
@@ -420,7 +420,7 @@ def register_jobs(
         jobid = jobid_future.result()
         if self.debug:
 
-            print(
+            logging.debug(
                 "Submitted array job {} with JobId {} and {} subjobs.".format(
                     batch_description, jobid, len(futs_with_output_paths)
                 ),