From 6ab79d9d5bed43e6e2d6b1b27ab319c02fa1716a Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <solipsis@pitrou.net>
Date: Wed, 23 Mar 2011 20:17:45 +0100
Subject: Allow "-j0" as an argument to regrtest, to automatically select an
 appropriate number of parallel workers.

---
 Lib/test/regrtest.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 1e72f80..a00f15a 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -374,6 +374,13 @@ def main(tests=None, testdir=None, verbose=0, quiet=False,
             forever = True
         elif o in ('-j', '--multiprocess'):
             use_mp = int(a)
+            if use_mp <= 0:
+                try:
+                    import multiprocessing
+                    # Use all cores + extras for tests that like to sleep
+                    use_mp = 2 + multiprocessing.cpu_count()
+                except (ImportError, NotImplementedError):
+                    use_mp = 3
         elif o == '--header':
             header = True
         elif o == '--slaveargs':
-- 
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