Doc/lib/libqueue.tex

   1 \section{Standard Module \module{Queue}}
   2 \stmodindex{Queue}
   3 \label{module-Queue}
   4
   5
   6 The \module{Queue} module implements a multi-producer, multi-consumer
   7 FIFO queue.  It is especially useful in threads programming when
   8 information must be exchanged safely between multiple threads.  The
   9 \class{Queue} class in this module implements all the required locking
  10 semantics.  It depends on the availability of thread support in
  11 Python.
  12
  13 The \module{Queue} module defines the following class and exception:
  14
  15
  16 \begin{classdesc}{Queue}{maxsize}
  17 Constructor for the class.  \var{maxsize} is an integer that sets the
  18 upperbound limit on the number of items that can be placed in the
  19 queue.  Insertion will block once this size has been reached, until
  20 queue items are consumed.  If \var{maxsize} is less than or equal to
  21 zero, the queue size is infinite.
  22 \end{classdesc}
  23
  24 \begin{excdesc}{Empty}
  25 Exception raised when non-blocking get (e.g. \method{get_nowait()}) is
  26 called on a \class{Queue} object which is empty, or for which the
  27 emptyiness cannot be determined (i.e. because the appropriate locks
  28 cannot be acquired).
  29 \end{excdesc}
  30
  31 \subsection{Queue Objects}
  32 \label{QueueObjects}
  33
  34 Class \class{Queue} implements queue objects and has the methods
  35 described below.  This class can be derived from in order to implement
  36 other queue organizations (e.g. stack) but the inheritable interface
  37 is not described here.  See the source code for details.  The public
  38 methods are:
  39
  40 \begin{methoddesc}{qsize}{}
  41 Returns the approximate size of the queue.  Because of multithreading
  42 semantics, this number is not reliable.
  43 \end{methoddesc}
  44
  45 \begin{methoddesc}{empty}{}
  46 Returns \code{1} if the queue is empty, \code{0} otherwise.  Because
  47 of multithreading semantics, this is not reliable.
  48 \end{methoddesc}
  49
  50 \begin{methoddesc}{full}{}
  51 Returns \code{1} if the queue is full, \code{0} otherwise.  Because of
  52 multithreading semantics, this is not reliable.
  53 \end{methoddesc}
  54
  55 \begin{methoddesc}{put}{item}
  56 Puts \var{item} into the queue.
  57 \end{methoddesc}
  58
  59 \begin{methoddesc}{get}{}
  60 Gets and returns an item from the queue, blocking if necessary until
  61 one is available.
  62 \end{methoddesc}
  63
  64 \begin{methoddesc}{get_nowait}{}
  65 Gets and returns an item from the queue if one is immediately
  66 available.  Raises an \exception{Empty} exception if the queue is
  67 empty or if the queue's emptiness cannot be determined.
  68 \end{methoddesc}