Doc/lib/libqueue.tex

   1 \section{\module{Queue} ---
   2          A synchronized queue class.}
   3 \declaremodule{standard}{Queue}
   4
   5 \modulesynopsis{A synchronized queue class.}
   6
   7
   8
   9 The \module{Queue} module implements a multi-producer, multi-consumer
  10 FIFO queue.  It is especially useful in threads programming when
  11 information must be exchanged safely between multiple threads.  The
  12 \class{Queue} class in this module implements all the required locking
  13 semantics.  It depends on the availability of thread support in
  14 Python.
  15
  16 The \module{Queue} module defines the following class and exception:
  17
  18
  19 \begin{classdesc}{Queue}{maxsize}
  20 Constructor for the class.  \var{maxsize} is an integer that sets the
  21 upperbound limit on the number of items that can be placed in the
  22 queue.  Insertion will block once this size has been reached, until
  23 queue items are consumed.  If \var{maxsize} is less than or equal to
  24 zero, the queue size is infinite.
  25 \end{classdesc}
  26
  27 \begin{excdesc}{Empty}
  28 Exception raised when non-blocking \method{get()} (or
  29 \method{get_nowait()}) is called on a \class{Queue} object which is
  30 empty or locked.
  31 \end{excdesc}
  32
  33 \begin{excdesc}{Full}
  34 Exception raised when non-blocking \method{put()} (or
  35 \method{get_nowait()}) is called on a \class{Queue} object which is
  36 full or locked.
  37 \end{excdesc}
  38
  39 \subsection{Queue Objects}
  40 \label{QueueObjects}
  41
  42 Class \class{Queue} implements queue objects and has the methods
  43 described below.  This class can be derived from in order to implement
  44 other queue organizations (e.g. stack) but the inheritable interface
  45 is not described here.  See the source code for details.  The public
  46 methods are:
  47
  48 \begin{methoddesc}{qsize}{}
  49 Return the approximate size of the queue.  Because of multithreading
  50 semantics, this number is not reliable.
  51 \end{methoddesc}
  52
  53 \begin{methoddesc}{empty}{}
  54 Return \code{1} if the queue is empty, \code{0} otherwise.  Because
  55 of multithreading semantics, this is not reliable.
  56 \end{methoddesc}
  57
  58 \begin{methoddesc}{full}{}
  59 Return \code{1} if the queue is full, \code{0} otherwise.  Because of
  60 multithreading semantics, this is not reliable.
  61 \end{methoddesc}
  62
  63 \begin{methoddesc}{put}{item\optional{, block}}
  64 Put \var{item} into the queue.  If optional argument \var{block} is 1
  65 (the default), block if necessary until a free slot is available.
  66 Otherwise (\var{block} is 0), put \var{item} on the queue if a free
  67 slot is immediately available, else raise the \exception{Full}
  68 exception.
  69 \end{methoddesc}
  70
  71 \begin{methoddesc}{put_nowait}{item}
  72 Equivalent to \code{put(\var{item}, 0)}.
  73 \end{methoddesc}
  74
  75 \begin{methoddesc}{get}{\optional{block}}
  76 Remove and return an item from the queue.  If optional argument
  77 \var{block} is 1 (the default), block if necessary until an item is
  78 available.  Otherwise (\var{block} is 0), return an item if one is
  79 immediately available, else raise the
  80 \exception{Empty} exception.
  81 \end{methoddesc}
  82
  83 \begin{methoddesc}{get_nowait}{}
  84 Equivalent to \code{get(0)}.
  85 \end{methoddesc}