多线程下的内存释放问题

问题由来，

考虑设计一个内存池类，http://www.ibm.com/developerworks/cn/linux/l-cn-ppp/index6.html?ca=drs-cn。

内存池类代码如下：

.h文件

 1 #pragma once
 2 
 3 
 4 #include <memory>
 5 #include <iostream>
 6 #include <windows.h>
 7 using namespace std;
 8 
 9 
10 #define USHORT    unsigned int
11 #define ULONG      unsigned long 
12 #define MEMPOOL_ALIGNMENT  4
13 
14 #pragma warning( disable : 4291 )
15 
16 struct MemoryBlock
17 {
18     unsigned short          nSize;
19     unsigned short          nFree;
20     unsigned short          nFirst;
21     //std::shared_ptr<MemoryBlock> pNext;
22     MemoryBlock*            pNext;
23     char                    aData[1];
24 
25     static void* operator new(size_t, unsigned short nTypes, unsigned short nUnitSize)
26     {
27         return ::operator new(sizeof(MemoryBlock) + nTypes * nUnitSize);
28     }
29 
30     static void  operator delete(void *p, size_t)
31     {
32         ::operator delete (p);
33     }
34 
35     MemoryBlock (unsigned short nTypes = 1, unsigned short nUnitSize = 0);
36     ~MemoryBlock() {}
37 
38 };
39 
40 class MemoryPool
41 {
42 private:
43     //std::shared_ptr<MemoryBlock>  pBlock;
44     MemoryBlock*            pBlock;
45     unsigned short          nUnitSize;
46     unsigned short          nInitCount;
47     unsigned short          nGrowSize;
48     CRITICAL_SECTION        allocSection;
49     CRITICAL_SECTION        freeSection;
50 
51 public:
52     static unsigned char   nMemoryIsDeleteFlag;            //标记MemoryPool内存是否释放
53 
54 public:
55                      MemoryPool( unsigned short nUnitSize,
56                                  unsigned short nInitCount = 1024,
57                                  unsigned short nGrowSize = 256 );
58                     ~MemoryPool();
59 
60     void*           Alloc();
61     void            Free( void* p );
62 };

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