Doc/lib/libqueue.tex

   1 \section{\module{Queue} ---
   2          A synchronized queue class}
   3
   4 \declaremodule{standard}{Queue}
   5 \modulesynopsis{A synchronized queue class.}
   6
   7
   8 The \module{Queue} module implements a multi-producer, multi-consumer
   9 FIFO queue.  It is especially useful in threads programming when
  10 information must be exchanged safely between multiple threads.  The
  11 \class{Queue} class in this module implements all the required locking
  12 semantics.  It depends on the availability of thread support in
  13 Python.
  14
  15 \begin{seealso}
  16     \seemodule{bisect}{PriorityQueue example using the Queue class}
  17 \end{seealso}
  18
  19 The \module{Queue} module defines the following class and exception:
  20
  21
  22 \begin{classdesc}{Queue}{maxsize}
  23 Constructor for the class.  \var{maxsize} is an integer that sets the
  24 upperbound limit on the number of items that can be placed in the
  25 queue.  Insertion will block once this size has been reached, until
  26 queue items are consumed.  If \var{maxsize} is less than or equal to
  27 zero, the queue size is infinite.
  28 \end{classdesc}
  29
  30 \begin{excdesc}{Empty}
  31 Exception raised when non-blocking \method{get()} (or
  32 \method{get_nowait()}) is called on a \class{Queue} object which is
  33 empty or locked.
  34 \end{excdesc}
  35
  36 \begin{excdesc}{Full}
  37 Exception raised when non-blocking \method{put()} (or
  38 \method{put_nowait()}) is called on a \class{Queue} object which is
  39 full or locked.
  40 \end{excdesc}
  41
  42 \subsection{Queue Objects}
  43 \label{QueueObjects}
  44
  45 Class \class{Queue} implements queue objects and has the methods
  46 described below.  This class can be derived from in order to implement
  47 other queue organizations (e.g. stack) but the inheritable interface
  48 is not described here.  See the source code for details.  The public
  49 methods are:
  50
  51 \begin{methoddesc}{qsize}{}
  52 Return the approximate size of the queue.  Because of multithreading
  53 semantics, this number is not reliable.
  54 \end{methoddesc}
  55
  56 \begin{methoddesc}{empty}{}
  57 Return \code{True} if the queue is empty, \code{False} otherwise.
  58 Becauseof multithreading semantics, this is not reliable.
  59 \end{methoddesc}
  60
  61 \begin{methoddesc}{full}{}
  62 Return \code{True} if the queue is full, \code{False} otherwise.
  63 Because of multithreading semantics, this is not reliable.
  64 \end{methoddesc}
  65
  66 \begin{methoddesc}{put}{item\optional{, block\optional{, timeout}}}
  67 Put \var{item} into the queue. If optional args \var{block} is true
  68 and \var{timeout} is None (the default), block if necessary until a
  69 free slot is available. If \var{timeout} is a positive number, it
  70 blocks at most \var{timeout} seconds and raises the \exception{Full}
  71 exception if no free slot was available within that time.
  72 Otherwise (\var{block} is false), put an item on the queue if a free
  73 slot is immediately available, else raise the \exception{Full}
  74 exception (\var{timeout} is ignored in that case).
  75
  76 \versionadded[the timeout parameter]{2.3}
  77
  78 \end{methoddesc}
  79
  80 \begin{methoddesc}{put_nowait}{item}
  81 Equivalent to \code{put(\var{item}, False)}.
  82 \end{methoddesc}
  83
  84 \begin{methoddesc}{get}{\optional{block\optional{, timeout}}}
  85 Remove and return an item from the queue. If optional args
  86 \var{block} is true and \var{timeout} is None (the default),
  87 block if necessary until an item is available. If \var{timeout} is
  88 a positive number, it blocks at most \var{timeout} seconds and raises
  89 the \exception{Empty} exception if no item was available within that
  90 time. Otherwise (\var{block} is false), return an item if one is
  91 immediately available, else raise the \exception{Empty} exception
  92 (\var{timeout} is ignored in that case).
  93
  94 \versionadded[the timeout parameter]{2.3}
  95
  96 \end{methoddesc}
  97
  98 \begin{methoddesc}{get_nowait}{}
  99 Equivalent to \code{get(False)}.
 100 \end{methoddesc}