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Add comments explaining thread unsafety of this code.

This commit is contained in:
Guido van Rossum 1998-05-29 17:51:59 +00:00
parent d03e1197cb
commit cc20b76ad0
1 changed files with 10 additions and 0 deletions
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10
Lib/whrandom.py
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@ -29,6 +29,13 @@
# Adrian Baddeley. # Adrian Baddeley.
# Multi-threading note: the random number generator used here is not
# thread-safe; it is possible that nearly simultaneous calls in
# different theads return the same random value. 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.)
class whrandom: class whrandom:
# #
# Initialize an instance. # Initialize an instance.
@ -60,6 +67,8 @@ def seed(self, x = 0, y = 0, z = 0):
# Get the next random number in the range [0.0, 1.0). # Get the next random number in the range [0.0, 1.0).
# #
def random(self): def random(self):
# This part is thread-unsafe:
# BEGIN CRITICAL SECTION
x, y, z = self._seed x, y, z = self._seed
# #
x = (171 * x) % 30269 x = (171 * x) % 30269
@ -67,6 +76,7 @@ def random(self):
z = (170 * z) % 30323 z = (170 * z) % 30323
# #
self._seed = x, y, z self._seed = x, y, z
# END CRITICAL SECTION
# #
return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0 return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0
# #