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Bug #788520: Queue class has logic error when non-blocking

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I don't agree it had a bug (see the report), so this is *not* a candidate
for backporting, but the docs were confusing and the Queue implementation
was old enough to vote.

Rewrote put/put_nowait/get/get_nowait from scratch, to use a pair of
Conditions (not_full and not_empty), sharing a common mutex.  The code
is 1/4 the size now, and 6.25x easier to understand.  For blocking
with timeout, we also get to reuse (indirectly) the tedious timeout
code from threading.Condition.  The Full and Empty exceptions raised
by non-blocking calls are now easy (instead of nearly impossible) to
explain truthfully:  Full is raised if and only if the Queue truly
is full when the non-blocking put call checks the queue size, and
similarly for Empty versus non-blocking get.

What I don't know is whether the new implementation is slower (or
faster) than the old one.  I don't really care.  Anyone who cares
a lot is encouraged to check that.
This commit is contained in:
Tim Peters 2004-07-12 00:45:14 +00:00
parent 183dabcd73
commit 5af0e41482
3 changed files with 82 additions and 94 deletions
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6
Doc/lib/libqueue.tex
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@ -26,13 +26,13 @@ zero, the queue size is infinite.
\begin{excdesc}{Empty}
Exception raised when non-blocking \method{get()} (or
\method{get_nowait()}) is called on a \class{Queue} object which is
empty or locked.
empty.
\end{excdesc}
\begin{excdesc}{Full}
Exception raised when non-blocking \method{put()} (or
\method{put_nowait()}) is called on a \class{Queue} object which is
full or locked.
full.
\end{excdesc}
\subsection{Queue Objects}
@ -51,7 +51,7 @@ semantics, this number is not reliable.
\begin{methoddesc}{empty}{}
Return \code{True} if the queue is empty, \code{False} otherwise.
Becauseof multithreading semantics, this is not reliable.
Because of multithreading semantics, this is not reliable.
\end{methoddesc}
\begin{methoddesc}{full}{}