add --jobs option to autoupdate

pre_commit/xargs.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import concurrent.futures
 import contextlib
 import math
+import multiprocessing
 import os
 import subprocess
 import sys
@@ -22,6 +23,13 @@ TArg = TypeVar('TArg')
 TRet = TypeVar('TRet')
 
 
+def cpu_count() -> int:
+    try:
+        return multiprocessing.cpu_count()
+    except NotImplementedError:
+        return 1
+
+
 def _environ_size(_env: MutableMapping[str, str] | None = None) -> int:
     environ = _env if _env is not None else getattr(os, 'environb', os.environ)
     size = 8 * len(environ)  # number of pointers in `envp`