Allow automatically determining the number of threads

docs/news.d/1039.feature.rst

@@ -0,0 +1 @@
+It is possible to use all logical CPUs by passing `-p0` (`--num-threads=0`). See `multiprocessing.cpu_count` for how the number is determined.

docs/run/src/run.py

@@ -9,6 +9,7 @@
 from pathlib import Path
 from vunit import VUnit, VUnitCLI
 from io import StringIO
+from multiprocessing import cpu_count
 import sys
 import re
 from tools.doc_support import highlight_code, highlight_log, LogRegistry
@@ -194,8 +195,8 @@ def _post_run(results):
             test_case_names = list(test_case_names)
             test_case_names.sort()
             name = "_".join(test_case_names)
-            if args.num_threads > 1:
-                options += f" -p{args.num_threads}"
+            if args.num_threads != 1:
+                options += f" -p{args.num_threads or cpu_count()}"
             if len(test_case_names) == 1:
                 (root / f"{name}_stdout.txt").write_text(f"> python run.py{options}\n" + std_out)
             else:

vunit/sim_if/nvc.py

@@ -8,6 +8,7 @@
 Interface for NVC simulator
 """
 
+from multiprocessing import cpu_count
 from pathlib import Path
 from os import environ, makedirs, remove
 import logging
@@ -95,7 +96,7 @@ def __init__(  # pylint: disable=too-many-arguments
 
         # Allow NVC to scale its worker thread count based on the number
         # of VUnit threads and the number of available CPUs.
-        environ["NVC_CONCURRENT_JOBS"] = str(num_threads)
+        environ["NVC_CONCURRENT_JOBS"] = str(num_threads or cpu_count())
 
     def has_valid_exit_code(self):  # pylint: disable=arguments-differ
         """

vunit/test/runner.py

@@ -9,6 +9,7 @@
 """
 
 import os
+from multiprocessing import cpu_count
 from pathlib import Path
 import traceback
 import threading
@@ -56,7 +57,7 @@ def __init__(  # pylint: disable=too-many-arguments
             self.VERBOSITY_VERBOSE,
         )
         self._verbosity = verbosity
-        self._num_threads = num_threads
+        self._num_threads = num_threads or cpu_count()
         self._stdout = sys.stdout
         self._stdout_ansi = wrap(self._stdout, use_color=not no_color)
         self._stderr = sys.stderr

vunit/vunit_cli.py

@@ -225,10 +225,12 @@ def _create_argument_parser(description=None, for_documentation=False):
     parser.add_argument(
         "-p",
         "--num-threads",
-        type=positive_int,
+        type=nonnegative_int,
         default=1,
         help=(
-            "Number of tests to run in parallel. " "Test output is not continuously written in verbose mode with p > 1"
+            "Number of tests to run in parallel. "
+            "Test output is not continuously written in verbose mode with p != 1. "
+            "p = 0 uses all logical CPUs."
         ),
     )
 
@@ -249,16 +251,16 @@ def _create_argument_parser(description=None, for_documentation=False):
     return parser
 
 
-def positive_int(val):
+def nonnegative_int(val):
     """
-    ArgumentParse positive int check
+    ArgumentParse non-negative int check
     """
     try:
         ival = int(val)
-        assert ival > 0
+        assert ival >= 0
         return ival
     except (ValueError, AssertionError) as exv:
-        raise argparse.ArgumentTypeError(f"'{val!s}' is not a valid positive int") from exv
+        raise argparse.ArgumentTypeError(f"'{val!s}' is not a valid non-negative int") from exv
 
 
 def _parser_for_documentation():