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Fix bugs introduced by rewrite (in particular, time-based initialization

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got broken).  Also added new method .jumpahead(N).  This finally gives us
a semi-decent answer to how Python's RNGs can be used safely and efficiently
in multithreaded programs (although it requires the user to use the new
machinery!).
This commit is contained in:
Tim Peters 2001-01-25 06:23:18 +00:00
parent d7b5e88e8e
commit d52269bfd0
3 changed files with 67 additions and 17 deletions
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27
Doc/lib/librandom.tex
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@ -33,14 +33,15 @@ Else, because no critical sections are implemented internally, calls
from different threads may see the same return values.
The functions supplied by this module are actually bound methods of a
hidden instance of the \var{random.Random} class. You can instantiate
your own instances of \var{Random} to get generators that don't share state.
This may be especially useful for multi-threaded programs, although there's
no simple way to seed the distinct generators to ensure that the generated
sequences won't overlap. Class \var{Random} can also be subclassed if you
want to use a different basic generator of your own devising: in that
case, override the \method{random()}, \method{seed()}, \method{getstate()}
and \method{setstate()} methods.
hidden instance of the \var{random.Random} class. You can instantiate your
own instances of \var{Random} to get generators that don't share state.
This is especially useful for multi-threaded programs, creating a different
instance of \var{Random} for each thread, and using the \method{jumpahead()}
method to ensure that the generated sequences seen by each thread don't
overlap. Class \var{Random} can also be subclassed if you want to use a
different basic generator of your own devising: in that case, override the
\method{random()}, \method{seed()}, \method{getstate()},
\method{setstate()} and \method{jumpahead()} methods.
Bookkeeping functions:
@ -68,6 +69,16 @@ Bookkeeping functions:
of the generate to what it was at the time \code{setstate()} was called.
\end{funcdesc}
\begin{funcdesc}{jumpahead}{n}
Change the internal state to what it would be if \code{random()} were
called n times, but do so quickly. \var{n} is a non-negative integer.
This is most useful in multi-threaded programs, in conjuction with
multiple instances of the \var{Random} class: \method{setstate()} or
\method{seed()} can be used to force all instances into the same
internal state, and then \method{jumpahead()} can be used to force the
instances' states as far apart as you like (up to the period of the
generator).
\end{funcdesc}
Functions for integers: