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