From ef63b220a114b166acdf663624c962a36b0577fc Mon Sep 17 00:00:00 2001
From: Oscar Gustafsson <oscar.gustafsson@gmail.com>
Date: Thu, 11 Jul 2024 12:56:16 +0200
Subject: [PATCH] Allow automatically determining the number of threads

---
 docs/news.d/1039.feature.rst |  1 +
 docs/run/src/run.py          |  5 +++--
 vunit/sim_if/nvc.py          |  3 ++-
 vunit/test/runner.py         |  3 ++-
 vunit/vunit_cli.py           | 14 ++++++++------
 5 files changed, 16 insertions(+), 10 deletions(-)
 create mode 100644 docs/news.d/1039.feature.rst

diff --git a/docs/news.d/1039.feature.rst b/docs/news.d/1039.feature.rst
new file mode 100644
index 000000000..c93b56d3f
--- /dev/null
+++ b/docs/news.d/1039.feature.rst
@@ -0,0 +1 @@
+It is possible to use all CPUs by passing `-p0` (`--num-threads=0`). See `multiprocessing.cpu_count` for how the number is determined.
\ No newline at end of file
diff --git a/docs/run/src/run.py b/docs/run/src/run.py
index 47abfd7da..ba58bbe86 100644
--- a/docs/run/src/run.py
+++ b/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:
diff --git a/vunit/sim_if/nvc.py b/vunit/sim_if/nvc.py
index 8f64ecae3..32bd9d36c 100644
--- a/vunit/sim_if/nvc.py
+++ b/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
         """
diff --git a/vunit/test/runner.py b/vunit/test/runner.py
index 5fa35af31..32b4a3950 100644
--- a/vunit/test/runner.py
+++ b/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
diff --git a/vunit/vunit_cli.py b/vunit/vunit_cli.py
index b604b0b43..e54ddb5a6 100644
--- a/vunit/vunit_cli.py
+++ b/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 means to use the number of available cores."
         ),
     )
 
@@ -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():