c++ simple "Garbage Collector"

 1 #include "MemMgr.h"
 2 
 3 #include <iostream>
 4 
 5 using namespace std;
 6 
 7 class Box
 8 {
 9     public:
10         void dosomething() { cout << "Box dosomething" << endl; }
11         Box() { cout << "Box cons" << endl; }
12         ~Box() { cout << "Box des" << endl; }
13 };
14 
15 Ptr<Box> global;
16 MemMgr mgr;
17 
18 
19 Ptr<Box> func() {
20     Ptr<Box> pb = mgr.regist(new Box());
21     return pb;
22 }
23 
24 
25 
26 int main()
27 {
28     Ptr<Box> p = func();
29     p->dosomething();
30     (*p).dosomething();
31     Ptr<Box> p2 = p;
32     p2->dosomething();
33     cout << "end of main" << endl;
34     global = p2;
35     return 0;
36 }

  1 #ifndef MEMMGR_H
  2 #define MEMMGR_H
  3 
  4 #include <map>
  5 #include <cstdlib>
  6 #include <set>
  7 
  8 template <typename TYPE>
  9 class Ptr;
 10 
 11 /**
 12     MemMgr take the idea of Garbage Collector
 13     from the Java language. It‘s just much simple
 14     and limited.
 15 */
 16 class MemMgr
 17 {
 18     template <typename T> friend class Ptr;
 19     private:
 20         typedef unsigned long count;
 21         template <typename T> void login(T* ptr_obj);
 22         template <typename T> void logout(T* ptr_obj);
 23         std::map<void*, count> cmap;
 24     public:
 25         MemMgr();
 26         /**
 27             Client is responsible to ensure obj is in the heap,
 28             and make sure only use Ptr objects rather than ordinary
 29             pointers when manipulating objects managed by MemMgr.
 30 
 31             If MemMgr is destroyed before any Ptr object managed
 32             by it, all Ptr objects managed by that MemMgr are all
 33             dangled pointers, this eventually leads to memory leak.
 34             So it‘s crucial to make sure MemMgr is not destroyed
 35             before ALL Ptr objects managed by it are destroyed.
 36 
 37             Otherwise the behavior of the MemMgr is undefined.
 38         */
 39         template <typename T> Ptr<T> regist(T *obj);
 40         ~MemMgr();
 41 
 42 };
 43 
 44 /**
 45     Ptr acts like a reference in java.
 46 */
 47 template <typename TYPE>
 48 class Ptr {
 49 
 50     friend class MemMgr;
 51 
 52     public:
 53         Ptr& operator=(const Ptr<TYPE> &copy)
 54         {
 55             if(copy) {
 56                 logout();
 57                 obj = copy.obj;
 58                 mgr = copy.mgr;
 59                 copy.mgr->login(&obj);
 60             } // else leaves obj and mgr NULL
 61             return *this;
 62         }
 63         TYPE* operator->() { return obj; }
 64         TYPE& operator*() { return *obj; }
 65         const TYPE* operator->() const { return obj; }
 66         const TYPE& operator*() const { return *obj; }
 67         operator bool() const { return ( (obj != NULL) && (mgr != NULL) ); }
 68 
 69         Ptr(): obj(NULL), mgr(NULL) {}
 70         Ptr(const Ptr &copy): obj(NULL), mgr(NULL)
 71         {
 72             if(copy) {
 73                 obj = copy.obj;
 74                 mgr = copy.mgr;
 75                 copy.mgr->login(obj);
 76             }
 77         }
 78         ~Ptr()
 79         {
 80             logout();
 81         }
 82     private:
 83         Ptr(TYPE *_obj, MemMgr *_mgr): obj(_obj), mgr(_mgr)
 84         {
 85             mgr->login(obj);
 86         }
 87         void logout() {
 88             if (*this) {
 89                 mgr->logout(obj); obj = NULL; mgr = NULL;
 90             }
 91         }
 92         TYPE *obj;
 93         MemMgr *mgr;
 94 };
 95 
 96 
 97 template <typename T> Ptr<T> MemMgr::regist(T *obj)
 98 {
 99     return Ptr<T>(obj, this);
100 }
101 
102 template <typename T>
103 void MemMgr::login(T* ptr_obj)
104 {
105     std::map<void*, count>::iterator iter = cmap.find(ptr_obj);
106     if (iter != cmap.end()) {
107         ++(iter->second);
108     } else {
109         cmap.insert(std::pair<void*, count>(ptr_obj, 1));
110     }
111 }
112 
113 template <typename T>
114 void MemMgr::logout(T* ptr_obj)
115 {
116     std::map<void*, count>::iterator iter = cmap.find(ptr_obj);
117     if (iter != cmap.end()) {
118         --(iter->second);
119         if (iter->second == 0) {
120             T *p = (T*)(iter->first);
121             delete p;
122         }
123     }
124 }
125 
126 #endif // MEMMGR_H

 1 #include "MemMgr.h"
 2 
 3 #include <iostream>
 4 
 5 using namespace std;
 6 
 7 MemMgr::MemMgr()
 8 {
 9     cout << "MemMgr cons" << endl;
10 }
11 
12 MemMgr::~MemMgr()
13 {
14     cout << "MemMgr des" << endl;
15 }