Ensure random seeds are unique for multiprocessed sampling

changelog.md

@@ -1,6 +1,17 @@
 # COSMIC Changelog 
 ## Prepend only please!
 
+## 4.1.1
+
+- Additions/changes
+    -
+
+- Code cleanup
+    - 
+
+- Bug fixes
+    - Fixed issue from v3.7.6 where multiprocessing re-used random seeds across workers. This results in non-unique samples proportional to the number of cores that you used.
+
 ## 4.1.0
 
 - Additions/changes

src/cosmic/_version.py

@@ -1 +1 @@
-__version__ = "4.1.0"
+__version__ = "4.1.1"

src/cosmic/sample/sampler/independent.py

@@ -24,6 +24,7 @@
 import pandas as pd
 import warnings
 from multiprocessing import Pool
+import os
 
 from cosmic import utils
 
@@ -218,7 +219,7 @@ def get_independent_sampler(
 
     # if no pool was passed in, but nproc > 1, create a pool
     if not pool_existed_already and nproc > 1:
-        pool = Pool(nproc)
+        pool = Pool(nproc, initializer=_init_worker)
 
     # if there's no pool, simply pass the arguments to the worker
     if pool is None:
@@ -479,6 +480,11 @@ def _independent_sampler_worker(
         n_binaries
     )
 
+def _init_worker():
+    """Ensure that each worker process has a different random seed."""
+    np.random.seed(np.random.get_state()[1][0] + os.getpid())
+
+
 
 register_sampler(
     "independent",

src/cosmic/tests/test_sample.py

@@ -644,6 +644,21 @@ def test_m2min_qmin(self):
             it_fails = True
         self.assertFalse(it_fails)
 
+    def test_samples_unique(self):
+        # ensure that samples are unique, both serial and parallel
+        np.random.seed(2)
+
+        for nproc in [1, 2]:
+            ibt = InitialBinaryTable.sampler(
+                'independent', range(16), range(16),
+                binfrac_model=1.0, primary_model='kroupa01',
+                ecc_model='sana12', porb_model='sana12',
+                qmin=-1, SF_start=13700.0, SF_duration=0.0,
+                met=0.02, size=10_000, nproc=nproc
+            )[0]
+
+            self.assertTrue(len(ibt) == len(ibt.drop_duplicates()))
+
 class TestCMCSample(unittest.TestCase):
     def test_plummer_profile(self):
         np.random.seed(2)