src/base/Subscription.h

   1 /*
   2  * Copyright (C) 1996-2019 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_BASE_SUBSCRIPTION_H
  10 #define _SQUID_BASE_SUBSCRIPTION_H
  11
  12 #include "base/AsyncCall.h"
  13
  14 /** API for creating a series of AsyncCalls.
  15  * This is necessary because the same AsyncCall callback must not be
  16  * fired multiple times.
  17  *
  18  * The call producer needs to accept and store a Subscription::Pointer.
  19  * It also should provide some mechanism for adding/removing/changing
  20  * the stored Subscription::Pointer.
  21  *
  22  * The callback() method of Subscription::Pointer will spawn AsyncCall
  23  * to be filled out and scheduled as needed.
  24  */
  25 class Subscription: public RefCountable
  26 {
  27 public:
  28     typedef RefCount<Subscription> Pointer;
  29
  30     /** returns a call object to be used for the next call back.
  31      * Child implementations must ensure the Call pointer produced
  32      * is not NULL.
  33      */
  34     virtual AsyncCall::Pointer callback() const = 0;
  35 };
  36
  37 /** Implements Subscription API using Call's copy constructor.
  38  *
  39  * The subscriber creates one of these using a specific callback
  40  * type and instance. The subscription object is then passed to a
  41  * producer/factory which will use this API to generate calls.
  42  * A subscription may be passed to multiple producers.
  43  *
  44  * Call_ must have a copy constructor.
  45  * A pointer to Call_ must be convertable to AsyncCall::Pointer
  46  */
  47 template<class Call_>
  48 class CallSubscription: public Subscription
  49 {
  50 public:
  51     /// Must be passed an object. nil pointers are not permitted.
  52     explicit CallSubscription(const RefCount<Call_> &aCall) : call(aCall) { assert(aCall != NULL); }
  53     virtual AsyncCall::Pointer callback() const { return new Call_(*call); }
  54
  55 private:
  56     const RefCount<Call_> call; ///< gets copied to create callback calls
  57 };
  58
  59 #endif /* _SQUID_BASE_SUBSCRIPTION_H */
  60