src/base/InstanceId.h

   1 #ifndef SQUID_BASE_INSTANCE_ID_H
   2 #define SQUID_BASE_INSTANCE_ID_H
   3
   4 #include <iosfwd>
   5
   6 /** Identifier for class instances
   7  *   - unique IDs for a large number of concurrent instances, but may wrap;
   8  *   - useful for debugging and insecure request/response matching;
   9  *   - sequential IDs within a class except when wrapping;
  10  *   - always positive IDs.
  11  *  \todo: add storage type parameter to support configurable Value types?
  12  *  \todo: add creation/destruction debugging?
  13  */
  14 template <class Class>
  15 class InstanceId
  16 {
  17 public:
  18     typedef unsigned int Value; ///< id storage type; \todo: parameterize?
  19
  20     InstanceId(): value(++Last ? Last : ++Last) {}
  21
  22     operator Value() const { return value; }
  23     bool operator ==(const InstanceId &o) const { return value == o.value; }
  24     bool operator !=(const InstanceId &o) const { return !(*this == o); }
  25     void change() {value = ++Last ? Last : ++Last;}
  26
  27     /// prints Prefix followed by ID value; \todo: use HEX for value printing?
  28     std::ostream &print(std::ostream &os) const;
  29
  30 public:
  31     static const char *Prefix; ///< Class shorthand string for debugging
  32     Value value; ///< instance identifier
  33
  34 private:
  35     InstanceId(const InstanceId& right); ///< not implemented; IDs are unique
  36     InstanceId& operator=(const InstanceId &right); ///< not implemented
  37
  38 private:
  39     static Value Last; ///< the last used ID value
  40 };
  41
  42 /// convenience macro to instantiate Class-specific stuff in .cc files
  43 #define InstanceIdDefinitions(Class, prefix) \
  44     template<> const char *InstanceId<Class>::Prefix = prefix; \
  45     template<> InstanceId<Class>::Value InstanceId<Class>::Last = 0; \
  46     template<> std::ostream & \
  47     InstanceId<Class>::print(std::ostream &os) const { \
  48         return os << Prefix << value; \
  49     }
  50
  51
  52 /// print the id
  53 template <class Class>
  54 inline
  55 std::ostream &operator <<(std::ostream &os, const InstanceId<Class> &id)
  56 {
  57     return id.print(os);
  58 }
  59
  60
  61 #endif /* SQUID_BASE_INSTANCE_ID_H */