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Patch #572628: Optional timeouts for put and get.
author Martin v. Löwis <martin@v.loewis.de>
date Tue, 15 Oct 2002 15:11:13 +0000
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children 63fa60f2d61c
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1 \section{\module{Queue} ---
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2 A synchronized queue class}
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3
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4 \declaremodule{standard}{Queue}
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5 \modulesynopsis{A synchronized queue class.}
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6
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8 The \module{Queue} module implements a multi-producer, multi-consumer
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9 FIFO queue. It is especially useful in threads programming when
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10 information must be exchanged safely between multiple threads. The
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11 \class{Queue} class in this module implements all the required locking
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12 semantics. It depends on the availability of thread support in
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13 Python.
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14
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15 \begin{seealso}
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16 \seemodule{bisect}{PriorityQueue example using the Queue class}
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17 \end{seealso}
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18
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19 The \module{Queue} module defines the following class and exception:
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20
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21
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22 \begin{classdesc}{Queue}{maxsize}
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23 Constructor for the class. \var{maxsize} is an integer that sets the
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24 upperbound limit on the number of items that can be placed in the
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25 queue. Insertion will block once this size has been reached, until
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26 queue items are consumed. If \var{maxsize} is less than or equal to
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27 zero, the queue size is infinite.
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28 \end{classdesc}
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29
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30 \begin{excdesc}{Empty}
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31 Exception raised when non-blocking \method{get()} (or
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32 \method{get_nowait()}) is called on a \class{Queue} object which is
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33 empty or locked.
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34 \end{excdesc}
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35
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36 \begin{excdesc}{Full}
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37 Exception raised when non-blocking \method{put()} (or
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38 \method{put_nowait()}) is called on a \class{Queue} object which is
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39 full or locked.
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40 \end{excdesc}
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41
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42 \subsection{Queue Objects}
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43 \label{QueueObjects}
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44
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45 Class \class{Queue} implements queue objects and has the methods
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46 described below. This class can be derived from in order to implement
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47 other queue organizations (e.g. stack) but the inheritable interface
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48 is not described here. See the source code for details. The public
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49 methods are:
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50
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51 \begin{methoddesc}{qsize}{}
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52 Return the approximate size of the queue. Because of multithreading
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53 semantics, this number is not reliable.
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54 \end{methoddesc}
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55
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56 \begin{methoddesc}{empty}{}
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57 Return \code{True} if the queue is empty, \code{False} otherwise.
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58 Becauseof multithreading semantics, this is not reliable.
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59 \end{methoddesc}
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60
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61 \begin{methoddesc}{full}{}
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62 Return \code{True} if the queue is full, \code{False} otherwise.
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63 Because of multithreading semantics, this is not reliable.
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64 \end{methoddesc}
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65
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66 \begin{methoddesc}{put}{item\optional{, block\optional{, timeout}}}
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67 Put \var{item} into the queue. If optional args \var{block} is true
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68 and \var{timeout} is None (the default), block if necessary until a
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69 free slot is available. If \var{timeout} is a positive number, it
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70 blocks at most \var{timeout} seconds and raises the \exception{Full}
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71 exception if no free slot was available within that time.
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72 Otherwise (\var{block} is false), put an item on the queue if a free
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73 slot is immediately available, else raise the \exception{Full}
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74 exception (\var{timeout} is ignored in that case).
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75
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76 \versionadded[the timeout parameter]{2.3}
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77
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78 \end{methoddesc}
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79
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80 \begin{methoddesc}{put_nowait}{item}
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81 Equivalent to \code{put(\var{item}, False)}.
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82 \end{methoddesc}
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83
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84 \begin{methoddesc}{get}{\optional{block\optional{, timeout}}}
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85 Remove and return an item from the queue. If optional args
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86 \var{block} is true and \var{timeout} is None (the default),
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87 block if necessary until an item is available. If \var{timeout} is
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88 a positive number, it blocks at most \var{timeout} seconds and raises
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89 the \exception{Empty} exception if no item was available within that
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90 time. Otherwise (\var{block} is false), return an item if one is
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91 immediately available, else raise the \exception{Empty} exception
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92 (\var{timeout} is ignored in that case).
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93
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94 \versionadded[the timeout parameter]{2.3}
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95
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96 \end{methoddesc}
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97
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98 \begin{methoddesc}{get_nowait}{}
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99 Equivalent to \code{get(False)}.
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100 \end{methoddesc}