zypp/Callback.h

   1 /*---------------------------------------------------------------------\
   2 |                          ____ _   __ __ ___                          |
   3 |                         |__  / \ / / . \ . \                         |
   4 |                           / / \ V /|  _/  _/                         |
   5 |                          / /__ | | | | | |                           |
   6 |                         /_____||_| |_| |_|                           |
   7 |                                                                      |
   8 \---------------------------------------------------------------------*/
   9 /** \file zypp/Callback.h
  10  *
  11 */
  12 #ifndef ZYPP_CALLBACK_H
  13 #define ZYPP_CALLBACK_H
  14
  15 #include "zypp/base/NonCopyable.h"
  16
  17 ///////////////////////////////////////////////////////////////////
  18 namespace zypp
  19 { /////////////////////////////////////////////////////////////////
  20
  21   /** \todo Eliminate this! */
  22   namespace HACK {
  23     class Callback
  24     {
  25     };
  26   } // namespace HACK
  27
  28   ///////////////////////////////////////////////////////////////////
  29   /** Callbacks light.
  30    *
  31    * \par The task report structure (SENDER SIDE).
  32    *
  33    * A default constructible struct derived from callback::ReportBase.
  34    * It \b must \b not conatin any data, just virtual methods.
  35    *
  36    * These are the functions the sender invokes, and which will be forwarded
  37    * to some receiver. If no receiver is present, the defined default
  38    * implementations are invoked.
  39    *
  40    * For methods returning non-void, define a reasonable return value,
  41    * because this is what you get back in case no receiver is listening.
  42    *
  43    * That way the sending side does not need to know whether some receiver
  44    * is listening. And it enables the receiver to return a reasonable value,
  45    * in case he's got no idea, what to else to return.
  46    *
  47    * \code
  48    *   struct Foo : public callback::ReportBase
  49    *   {
  50    *     virtual void ping( int i )
  51    *     {}
  52    *     virtual int pong()
  53    *     { return -1; }
  54    *
  55    *   };
  56    * \endcode
  57    *
  58    * \par Sending a Task report (SENDER SIDE).
  59    *
  60    * Simply create a callback::SendReport<_Report>, where _Report
  61    * is your task report structure. Invoke the callback functions
  62    * as needed. That's it.
  63    *
  64    * \note Even creation and destruction of a callback::SendReport
  65    * are indicated to a receiver. So even in case of an Exception,
  66    * the receiver is able to recognize, that the task ended.
  67    * So don't create it without need.
  68    *
  69    * \code
  70    * {
  71    *   callback::SendReport<Foo> report;
  72    *   report->ping( 13 );
  73    *   int response = report->pong();
  74    * }
  75    * \endcode
  76    *
  77    * \par Receiving Task reports (RECEIVER SIDE).
  78    *
  79    * To receive task reports of type \c Foo the recipient class
  80    * derives from callback::ReceiveReport\<Foo\>. callback::ReceiveReport
  81    * inherits \c Foo and provides two additional virtual methods:
  82    *
  83    * \code
  84    *   virtual void reportbegin() {}
  85    *   virtual void reportend() {}
  86    * \endcode
  87    *
  88    * These two are automatically invoked, whenever the sender
  89    * creates a callback::SendReport instance, and when it gets
  90    * destructed. So even if the sending task is aborted without
  91    * sending an explicit notification, the reciever may notice it,
  92    * by overloading \c reportend.
  93    *
  94    * Overload the methods you're interested in.
  95    *
  96    * \note In case you must return some value and don't know which,
  97    * return the task structures default. The author of the task
  98    * structure had to provide this value, so it's probabely better
  99    * than anything you \e invent.
 100    * \code
 101    *   int somefunktion()
 102    *   {
 103    *     ...// don't know what to return?
 104    *     return Foo::somefunktion();
 105    *   }
 106    * \endcode
 107    *
 108    * \par Connecting the Receiver
 109    *
 110    * For this callback::ReceiveReport provides 4 methods:
 111    * \code
 112    *  void connect();
 113    *  void disconnect();
 114    *  bool connected() const;
 115    *  ReceiveReport * whoIsConnected() const;
 116    * \endcode
 117    *
 118    * \li \c connect Connect this ReceiveReport (in case some other
 119    * ReceiveReport is connected, it get disconneced. Remember its
 120    * a Callback light).
 121    * \li \c disconnect Disconnect this ReceiveReport in case it is
 122    * connected. If not connected nothing happens.
 123    * \li \c connected Test wheter this ReceiveReport is currently
 124    * connected.
 125    * \li \c whoIsConnected Return a 'ReceiveReport*' to the currently
 126    * connected ReceiveReport, or \c NULL if none is connected.
 127    *
 128   */
 129   namespace callback
 130   { /////////////////////////////////////////////////////////////////
 131
 132     /**  */
 133     struct ReportBase
 134     {
 135       virtual ~ReportBase()
 136       {}
 137     };
 138
 139     /**  */
 140     template<class _Report>
 141       class DistributeReport;
 142
 143     /**  */
 144     template<class _Report>
 145       struct ReceiveReport : public _Report
 146       {
 147         typedef DistributeReport<_Report> Distributor;
 148
 149         virtual ~ReceiveReport()
 150         { disconnect(); }
 151
 152         ReceiveReport * whoIsConnected() const
 153         { return Distributor::instance().getReceiver(); }
 154
 155         bool connected() const
 156         { return whoIsConnected() == this; }
 157
 158         void connect()
 159         { Distributor::instance().setReceiver( *this ); }
 160
 161         void disconnect()
 162         { Distributor::instance().unsetReceiver( *this ); }
 163
 164         virtual void reportbegin()
 165         {}
 166         virtual void reportend()
 167         {}
 168       };
 169
 170     /**  */
 171     template<class _Report>
 172       struct DistributeReport
 173       {
 174        public:
 175          typedef ReceiveReport<_Report> Receiver;
 176
 177          static DistributeReport & instance()
 178          {
 179            static DistributeReport _self;
 180            return _self;
 181          }
 182
 183          Receiver * getReceiver() const
 184          { return _receiver == &_noReceiver ? NULL : _receiver; }
 185
 186          void setReceiver( Receiver & rec_r )
 187          { _receiver = &rec_r; }
 188
 189          void unsetReceiver( Receiver & rec_r )
 190          { if ( _receiver == &rec_r ) noReceiver(); }
 191
 192          void noReceiver()
 193          { _receiver = &_noReceiver; }
 194
 195       public:
 196          Receiver * operator->()
 197          { return _receiver; }
 198
 199       private:
 200         DistributeReport()
 201         : _receiver( &_noReceiver )
 202         {}
 203         Receiver _noReceiver;
 204         Receiver * _receiver;
 205       };
 206
 207     /**  */
 208     template<class _Report>
 209       struct SendReport : private zypp::base::NonCopyable
 210       {
 211         typedef DistributeReport<_Report> Distributor;
 212
 213         SendReport()
 214         { Distributor::instance()->reportbegin(); }
 215
 216         ~SendReport()
 217         { Distributor::instance()->reportend(); }
 218
 219         Distributor & operator->()
 220         { return Distributor::instance(); }
 221       };
 222
 223     /** Temporarily connect a ReceiveReport then restore the previous one.
 224      *
 225      * Pass the ReceiveReport you want to connect temporarily
 226      * to the ctor. The ReceiveReport is connected, a previously
 227      * connected ReceiveReport is remembered and re-connected in
 228      * the dtor.
 229      * \code
 230      *  struct FooReceive : public callback::ReceiveReport<Foo>
 231      *  {..};
 232      *  struct FooReceive2 : public callback::ReceiveReport<Foo>
 233      *  {..};
 234      *
 235      *  FooReceive  r;
 236      *  FooReceive2 r2;
 237      *
 238      *  r.connect();
 239      *  ... // r receiving the report
 240      *  {
 241      *    callback::TempConnect<Foo> temp( r2 );
 242      *    ...// r2 receiving the report
 243      *  }
 244      *  ...// r receiving the report
 245      * \endcode
 246     */
 247     template<class _Report>
 248       struct TempConnect
 249       {
 250         typedef ReceiveReport<_Report>    Receiver;
 251         typedef DistributeReport<_Report> Distributor;
 252
 253         TempConnect( Receiver & rec_r )
 254         : _oldRec( Distributor::instance().getReceiver() )
 255         {
 256           rec_r.connect();
 257         }
 258
 259         ~TempConnect()
 260         {
 261           if ( _oldRec )
 262             Distributor::instance().setReceiver( *_oldRec );
 263           else
 264             Distributor::instance().noReceiver();
 265         }
 266       private:
 267         Receiver * _oldRec;
 268       };
 269
 270     /////////////////////////////////////////////////////////////////
 271   } // namespace callback
 272   ///////////////////////////////////////////////////////////////////
 273   /////////////////////////////////////////////////////////////////
 274 } // namespace zypp
 275 ///////////////////////////////////////////////////////////////////
 276 #endif // ZYPP_CALLBACK_H