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100 lines
3.6 KiB
TeX
100 lines
3.6 KiB
TeX
\section{\module{Queue} ---
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A synchronized queue class}
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\declaremodule{standard}{Queue}
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\modulesynopsis{A synchronized queue class.}
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The \module{Queue} module implements a multi-producer, multi-consumer
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FIFO queue. It is especially useful in threads programming when
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information must be exchanged safely between multiple threads. The
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\class{Queue} class in this module implements all the required locking
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semantics. It depends on the availability of thread support in
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Python.
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\begin{seealso}
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\seemodule{bisect}{PriorityQueue example using the Queue class}
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\end{seealso}
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The \module{Queue} module defines the following class and exception:
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\begin{classdesc}{Queue}{maxsize}
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Constructor for the class. \var{maxsize} is an integer that sets the
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upperbound limit on the number of items that can be placed in the
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queue. Insertion will block once this size has been reached, until
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queue items are consumed. If \var{maxsize} is less than or equal to
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zero, the queue size is infinite.
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\end{classdesc}
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\begin{excdesc}{Empty}
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Exception raised when non-blocking \method{get()} (or
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\method{get_nowait()}) is called on a \class{Queue} object which is
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empty or locked.
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\end{excdesc}
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\begin{excdesc}{Full}
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Exception raised when non-blocking \method{put()} (or
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\method{put_nowait()}) is called on a \class{Queue} object which is
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full or locked.
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\end{excdesc}
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\subsection{Queue Objects}
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\label{QueueObjects}
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Class \class{Queue} implements queue objects and has the methods
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described below. This class can be derived from in order to implement
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other queue organizations (e.g. stack) but the inheritable interface
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is not described here. See the source code for details. The public
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methods are:
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\begin{methoddesc}{qsize}{}
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Return the approximate size of the queue. Because of multithreading
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semantics, this number is not reliable.
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\end{methoddesc}
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\begin{methoddesc}{empty}{}
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Return \code{True} if the queue is empty, \code{False} otherwise.
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Becauseof multithreading semantics, this is not reliable.
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\end{methoddesc}
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\begin{methoddesc}{full}{}
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Return \code{True} if the queue is full, \code{False} otherwise.
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Because of multithreading semantics, this is not reliable.
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\end{methoddesc}
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\begin{methoddesc}{put}{item\optional{, block\optional{, timeout}}}
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Put \var{item} into the queue. If optional args \var{block} is true
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and \var{timeout} is None (the default), block if necessary until a
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free slot is available. If \var{timeout} is a positive number, it
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blocks at most \var{timeout} seconds and raises the \exception{Full}
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exception if no free slot was available within that time.
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Otherwise (\var{block} is false), put an item on the queue if a free
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slot is immediately available, else raise the \exception{Full}
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exception (\var{timeout} is ignored in that case).
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\versionadded[the timeout parameter]{2.3}
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\end{methoddesc}
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\begin{methoddesc}{put_nowait}{item}
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Equivalent to \code{put(\var{item}, False)}.
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\end{methoddesc}
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\begin{methoddesc}{get}{\optional{block\optional{, timeout}}}
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Remove and return an item from the queue. If optional args
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\var{block} is true and \var{timeout} is None (the default),
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block if necessary until an item is available. If \var{timeout} is
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a positive number, it blocks at most \var{timeout} seconds and raises
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the \exception{Empty} exception if no item was available within that
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time. Otherwise (\var{block} is false), return an item if one is
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immediately available, else raise the \exception{Empty} exception
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(\var{timeout} is ignored in that case).
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\versionadded[the timeout parameter]{2.3}
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\end{methoddesc}
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\begin{methoddesc}{get_nowait}{}
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Equivalent to \code{get(False)}.
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\end{methoddesc}
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