[impl]: Factor out logic to compute the number of threads/processes t…

…o use

libs/ccc/coef/impl.py

@@ -1,6 +1,8 @@
 """
 Contains function that implement the Clustermatch Correlation Coefficient (CCC).
 """
+from __future__ import annotations
+
 import os
 from concurrent.futures import ThreadPoolExecutor, as_completed, ProcessPoolExecutor
 from typing import Iterable, Union
@@ -515,6 +517,30 @@ def cdist_func(x, y):
     return max_ari_list, max_part_idx_list, pvalues
 
 
+def get_n_workers(n_jobs: int | None) -> int:
+    """
+    Helper function to get the number of workers for parallel processing.
+
+    Args:
+        n_jobs: value specified by the main ccc function.
+    """
+    n_cpu_cores = os.cpu_count()
+    if n_cpu_cores is None:
+        raise ValueError("Could not determine the number of CPU cores. Please specify a positive value of n_jobs")
+
+    n_workers = n_cpu_cores
+    if n_jobs is None:
+        return n_workers
+
+    n_workers = os.cpu_count() + n_jobs if n_jobs < 0 else n_jobs
+
+    if n_workers < 1:
+        raise ValueError(f"The number of threads/processes to use must be greater than 0. Got {n_workers}."
+                         "Please check the n_jobs argument provided")
+
+    return n_workers
+
+
 def ccc(
     x: NDArray,
     y: NDArray = None,
@@ -544,9 +570,10 @@ def ccc(
         n_chunks_threads_ratio: allows to modify how pairwise comparisons are
           split across different threads. It's given as the ratio parameter of
           function get_chunks.
-        n_jobs: number of CPU cores to use for parallelization. The value
+        n_jobs: number of CPU cores/threads to use for parallelization. The value
           None will use all available cores (`os.cpu_count()`), and negative
-          values will use `os.cpu_count() - n_jobs`. Default is 1.
+          values will use `os.cpu_count() + n_jobs` (exception will be raised
+          if this expression yields a result less than 1). Default is 1.
         pvalue_n_perms: if given, it computes the p-value of the
             coefficient using the given number of permutations.
         partitioning_executor: Executor type used for partitioning the data. It
@@ -596,6 +623,7 @@ def ccc(
     X_numerical_type = None
     if x.ndim == 1 and (y is not None and y.ndim == 1):
         # both x and y are 1d arrays
+        # TODO: remove assertions and raise exceptions
         assert x.shape == y.shape, "x and y need to be of the same size"
         n_objects = x.shape[0]
         n_features = 2
@@ -639,8 +667,7 @@ def ccc(
         raise ValueError("Wrong combination of parameters x and y")
 
     # get number of cores to use
-    n_jobs = os.cpu_count() if n_jobs is None else n_jobs
-    default_n_threads = (os.cpu_count() + n_jobs) if n_jobs < 0 else n_jobs
+    n_workers = get_n_workers(n_jobs)
 
     if internal_n_clusters is not None:
         _tmp_list = List()
@@ -675,11 +702,11 @@ def ccc(
     max_parts = np.zeros((n_features_comp, 2), dtype=np.uint64)
 
     with (
-        ThreadPoolExecutor(max_workers=default_n_threads) as executor,
-        ProcessPoolExecutor(max_workers=default_n_threads) as pexecutor,
+        ThreadPoolExecutor(max_workers=n_workers) as executor,
+        ProcessPoolExecutor(max_workers=n_workers) as pexecutor,
     ):
         map_func = map
-        if default_n_threads > 1:
+        if n_workers > 1:
             if partitioning_executor == "thread":
                 map_func = executor.map
             elif partitioning_executor == "process":
@@ -695,7 +722,7 @@ def ccc(
                 for f_idx in range(n_features)
                 for c_idx, c in enumerate(range_n_clusters)
             ],
-            default_n_threads,
+            n_workers,
             n_chunks_threads_ratio,
         )
 
@@ -732,7 +759,7 @@ def ccc(
         cdist_executor = False
         inner_executor = DummyExecutor()
 
-        if default_n_threads > 1:
+        if n_workers > 1:
             if n_features_comp == 1:
                 map_func = map
                 cdist_executor = executor
@@ -742,14 +769,14 @@ def ccc(
                 map_func = pexecutor.map
 
         # iterate over all chunks of object pairs and compute the coefficient
-        inputs = get_chunks(n_features_comp, default_n_threads, n_chunks_threads_ratio)
+        inputs = get_chunks(n_features_comp, n_workers, n_chunks_threads_ratio)
         inputs = [
             (
                 i,
                 n_features,
                 parts,
                 pvalue_n_perms,
-                default_n_threads,
+                n_workers,
                 n_chunks_threads_ratio,
                 cdist_executor,
                 inner_executor,

tests/test_coef.py

@@ -1,5 +1,6 @@
 from concurrent.futures import ThreadPoolExecutor
 from random import shuffle
+from unittest.mock import patch
 import time
 import os
 
@@ -19,6 +20,7 @@
     cdist_parts_basic,
     cdist_parts_parallel,
     get_chunks,
+    get_n_workers,
 )
 
 
@@ -1557,3 +1559,27 @@ def test_cm_with_too_few_objects():
         ccc(data, internal_n_clusters=3)
 
     assert "too few objects" in str(e.value)
+
+
+
+@pytest.mark.parametrize("n_jobs, cpu_count, expected", [
+    (None, 4, 4),
+    (2, 4, 2),
+    (-1, 4, 3),
+    (6, 4, 6),
+])
+def test_get_n_workers_valid(n_jobs, cpu_count, expected):
+    with patch('os.cpu_count', return_value=cpu_count):
+        assert get_n_workers(n_jobs) == expected
+
+
+@pytest.mark.parametrize("n_jobs, cpu_count, error_type, error_message", [
+    (0, 4, ValueError, "The number of threads/processes to use must be greater than 0. Got 0"),
+    (-5, 4, ValueError, "The number of threads/processes to use must be greater than 0. Got -1"),
+    (2, None, ValueError, "Could not determine the number of CPU cores. Please specify a positive value of n_jobs"),
+    (None, None, ValueError, "Could not determine the number of CPU cores. Please specify a positive value of n_jobs"),
+])
+def test_get_n_workers_invalid(n_jobs, cpu_count, error_type, error_message):
+    with patch('os.cpu_count', return_value=cpu_count):
+        with pytest.raises(error_type, match=error_message):
+            get_n_workers(n_jobs)