Make gauss() semi-thread-safe. It can still give duplicate results,
but it can no longer raise an exception when called by several threads
simultaneously.
diff --git a/Lib/random.py b/Lib/random.py
index d95c324..a19059c 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -15,6 +15,10 @@
# Translated from anonymously contributed C/C++ source.
+# Multi-threading note: the random number generator used here is not
+# thread-safe; it is possible that two calls return the same random
+# value. See whrandom.py for more info.
+
import whrandom
from whrandom import random, uniform, randint, choice # Also for export!
from math import log, exp, pi, e, sqrt, acos, cos, sin
@@ -243,12 +247,18 @@
# (Lambert Meertens)
# (corrected version; bug discovered by Mike Miller, fixed by LM)
+ # Multithreading note: When two threads call this function
+ # simultaneously, it is possible that they will receive the
+ # same return value. The window is very small though. To
+ # avoid this, you have to use a lock around all calls. (I
+ # didn't want to slow this down in the serial case by using a
+ # lock here.)
+
global gauss_next
- if gauss_next != None:
- z = gauss_next
- gauss_next = None
- else:
+ z = gauss_next
+ gauss_next = None
+ if z is None:
x2pi = random() * TWOPI
g2rad = sqrt(-2.0 * log(1.0 - random()))
z = cos(x2pi) * g2rad