src/AsyncEngine.h

   1
   2 /*
   3  * $Id: AsyncEngine.h,v 1.1 2006/08/12 01:43:10 robertc Exp $
   4  *
   5  *
   6  * SQUID Web Proxy Cache          http://www.squid-cache.org/
   7  * ----------------------------------------------------------
   8  *
   9  *  Squid is the result of efforts by numerous individuals from
  10  *  the Internet community; see the CONTRIBUTORS file for full
  11  *  details.   Many organizations have provided support for Squid's
  12  *  development; see the SPONSORS file for full details.  Squid is
  13  *  Copyrighted (C) 2001 by the Regents of the University of
  14  *  California; see the COPYRIGHT file for full details.  Squid
  15  *  incorporates software developed and/or copyrighted by other
  16  *  sources; see the CREDITS file for full details.
  17  *
  18  *  This program is free software; you can redistribute it and/or modify
  19  *  it under the terms of the GNU General Public License as published by
  20  *  the Free Software Foundation; either version 2 of the License, or
  21  *  (at your option) any later version.
  22  *
  23  *  This program is distributed in the hope that it will be useful,
  24  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  25  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  26  *  GNU General Public License for more details.
  27  *
  28  *  You should have received a copy of the GNU General Public License
  29  *  along with this program; if not, write to the Free Software
  30  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
  31  *
  32  */
  33
  34 #ifndef SQUID_ASYNCENGINE_H
  35 #define SQUID_ASYNCENGINE_H
  36
  37 #include "squid.h"
  38
  39
  40 /* Abstract interface for async engines which an event loop can utilise.
  41  *
  42  * Some implementations will be truely async, others like the event engine
  43  * will be pseudo async.
  44  */
  45
  46 class AsyncEngine
  47 {
  48
  49 public:
  50     /* error codes returned from checkEvents. If the return value is not
  51      * negative, then it is the requested delay until the next call. If it is
  52      * negative, it is one of the following codes:
  53      */
  54     enum CheckError {
  55         /* this engine is completely idle: it has no pending events, and nothing
  56          * registered with it that can create events
  57          */
  58         EVENT_IDLE = -1,
  59         /* some error has occured in this engine */
  60         EVENT_ERROR = -2,
  61     };
  62
  63     virtual ~AsyncEngine() {}
  64
  65     /* Check the engine for events. If there are events that have completed,
  66      * the engine should at this point hand them off to their dispatcher.
  67      * Engines that operate asynchronously - i.e. the DiskThreads engine -
  68      * should hand events off to their dispatcher as they arrive rather than
  69      * waiting for checkEvents to be called. Engines like poll and select should
  70      * use this call as the time to perform their checks with the OS for new
  71      * events.
  72      *
  73      * The return value is the status code of the event checking. If its a
  74      * non-negative value then it is used as hint for the minimum requested
  75      * time before checkEvents is called again. I.e. the event engine knows
  76      * how long it is until the next event will be scheduled - so it will
  77      * return that time (in milliseconds).
  78      *
  79      * The timeout value is a requested timeout for this engine - the engine
  80      * should not block for more than this period. (If it takes longer than the
  81      * timeout to do actual checks thats fine though undesirable).
  82      */
  83     virtual int checkEvents(int timeout) = 0;
  84 };
  85
  86 #endif /* SQUID_ASYNCENGINE_H */