Merge pull request #1026 from Ernaldis/multi-processing-bug-fix

Multi processing bug fix

CHANGELOG.md

@@ -1,7 +1,8 @@
 ## Release notes
 
-### 0.13.5 -- May 13, 2022
+### 0.13.5 -- May 19, 2022
 * Update - Import ABC from collections.abc for Python 3.10 compatibility
+* Bugfix - Fix multiprocessing value error (#1013) PR #1026
 
 ### 0.13.4 -- March, 28 2022
 * Add - Allow reading blobs produced by legacy 32-bit compiled mYm library for matlab. PR #995

datajoint/autopopulate.py

@@ -173,8 +173,7 @@ def populate(
         :param limit: if not None, check at most this many keys
         :param max_calls: if not None, populate at most this many keys
         :param display_progress: if True, report progress_bar
-        :param processes: number of processes to use. When set to a large number, then
-            uses as many as CPU cores
+        :param processes: number of processes to use. Set to None to use all cores
         :param make_kwargs: Keyword arguments which do not affect the result of computation
             to be passed down to each ``make()`` call. Computation arguments should be
             specified within the pipeline e.g. using a `dj.Lookup` table.
@@ -211,9 +210,10 @@ def handler(signum, frame):
 
         keys = keys[:max_calls]
         nkeys = len(keys)
+        if not nkeys:
+            return
 
-        if processes > 1:
-            processes = min(processes, nkeys, mp.cpu_count())
+        processes = min(*(_ for _ in (processes, nkeys, mp.cpu_count()) if _))
 
         error_list = []
         populate_kwargs = dict(

docs-parts/intro/Releases_lang1.rst

@@ -1,6 +1,7 @@
-0.13.5 -- May 13, 2022
+0.13.5 -- May 19, 2022
 ----------------------
 * Update - Import ABC from collections.abc for Python 3.10 compatibility
+* Bugfix - Fix multiprocessing value error (#1013) PR #1026
 
 0.13.4 -- March 28, 2022
 ----------------------

tests/test_autopopulate.py

@@ -69,6 +69,15 @@ def test_multi_processing(self):
             == len(self.subject) * self.experiment.fake_experiments_per_subject
         )
 
+    def test_max_multi_processing(self):
+        assert self.subject, "root tables are empty"
+        assert not self.experiment, "table already filled?"
+        self.experiment.populate(processes=None)
+        assert (
+            len(self.experiment)
+            == len(self.subject) * self.experiment.fake_experiments_per_subject
+        )
+
     @raises(DataJointError)
     def test_allow_insert(self):
         assert_true(self.subject, "root tables are empty")