src/AsyncEngine.h

   1 /*
   2  * Copyright (C) 1996-2018 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #ifndef SQUID_ASYNCENGINE_H
  10 #define SQUID_ASYNCENGINE_H
  11
  12 /* Abstract interface for async engines which an event loop can utilise.
  13  *
  14  * Some implementations will be truely async, others like the event engine
  15  * will be pseudo async.
  16  */
  17
  18 class AsyncEngine
  19 {
  20
  21 public:
  22     /* error codes returned from checkEvents. If the return value is not
  23      * negative, then it is the requested delay until the next call. If it is
  24      * negative, it is one of the following codes:
  25      */
  26     enum CheckError {
  27         /* this engine is completely idle: it has no pending events, and nothing
  28          * registered with it that can create events
  29          */
  30         EVENT_IDLE = -1,
  31         /* some error has occured in this engine */
  32         EVENT_ERROR = -2
  33     };
  34
  35     virtual ~AsyncEngine() {}
  36
  37     /* Check the engine for events. If there are events that have completed,
  38      * the engine should at this point hand them off to their dispatcher.
  39      * Engines that operate asynchronously - i.e. the DiskThreads engine -
  40      * should hand events off to their dispatcher as they arrive rather than
  41      * waiting for checkEvents to be called. Engines like poll and select should
  42      * use this call as the time to perform their checks with the OS for new
  43      * events.
  44      *
  45      * The return value is the status code of the event checking. If its a
  46      * non-negative value then it is used as hint for the minimum requested
  47      * time before checkEvents is called again. I.e. the event engine knows
  48      * how long it is until the next event will be scheduled - so it will
  49      * return that time (in milliseconds).
  50      *
  51      * The timeout value is a requested timeout for this engine - the engine
  52      * should not block for more than this period. (If it takes longer than the
  53      * timeout to do actual checks thats fine though undesirable).
  54      */
  55     virtual int checkEvents(int timeout) = 0;
  56 };
  57
  58 #endif /* SQUID_ASYNCENGINE_H */
  59