src/base/InstanceId.h

   1 /*
   2  * Copyright (C) 1996-2014 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_INSTANCE_ID_H
  10 #define SQUID_BASE_INSTANCE_ID_H
  11
  12 #include <iosfwd>
  13
  14 /** Identifier for class instances
  15  *   - unique IDs for a large number of concurrent instances, but may wrap;
  16  *   - useful for debugging and insecure request/response matching;
  17  *   - sequential IDs within a class except when wrapping;
  18  *   - always positive IDs.
  19  *  \todo: add storage type parameter to support configurable Value types?
  20  *  \todo: add creation/destruction debugging?
  21  */
  22 template <class Class>
  23 class InstanceId
  24 {
  25 public:
  26     typedef unsigned int Value; ///< id storage type; \todo: parameterize?
  27
  28     InstanceId(): value(++Last ? Last : ++Last) {}
  29
  30     operator Value() const { return value; }
  31     bool operator ==(const InstanceId &o) const { return value == o.value; }
  32     bool operator !=(const InstanceId &o) const { return !(*this == o); }
  33     void change() {value = ++Last ? Last : ++Last;}
  34
  35     /// prints Prefix followed by ID value; \todo: use HEX for value printing?
  36     std::ostream &print(std::ostream &os) const;
  37
  38 public:
  39     static const char *Prefix; ///< Class shorthand string for debugging
  40     Value value; ///< instance identifier
  41
  42 private:
  43     InstanceId(const InstanceId& right); ///< not implemented; IDs are unique
  44     InstanceId& operator=(const InstanceId &right); ///< not implemented
  45
  46 private:
  47     static Value Last; ///< the last used ID value
  48 };
  49
  50 /// convenience macro to instantiate Class-specific stuff in .cc files
  51 #define InstanceIdDefinitions(Class, prefix) \
  52     template<> const char *InstanceId<Class>::Prefix = prefix; \
  53     template<> InstanceId<Class>::Value InstanceId<Class>::Last = 0; \
  54     template<> std::ostream & \
  55     InstanceId<Class>::print(std::ostream &os) const { \
  56         return os << Prefix << value; \
  57     }
  58
  59 /// print the id
  60 template <class Class>
  61 inline
  62 std::ostream &operator <<(std::ostream &os, const InstanceId<Class> &id)
  63 {
  64     return id.print(os);
  65 }
  66
  67 #endif /* SQUID_BASE_INSTANCE_ID_H */