在Win32中管理虚拟内存——举例

红太狼 2022-04-23 10:54 163阅读 0赞

以下两个编程例子： 
    
    整块方式使用虚拟内存页 
    分块方式使用虚拟内存页 
    
    （一）整块方式，分以下两步
      (1)预留＋提交
      (2)释放
    #include <stdio.h>
    #include <windows.h>
    int main(int argc, char*argv[])
    {
     LPVOID lpvBase;      // base address of the test memory
     int i;
     for(i=0; ; i++)
     {
      lpvBase = VirtualAlloc(  // (1)
       NULL,     // system selects address
       102400,     // size of allocation
       MEM_RESERVE|MEM_COMMIT, // allocate reserved and committed pages
       PAGE_READWRITE);        // both read and write
      if (NULL == lpvBase )
      {
       printf("call VirtualAlloc fail!\n");
       exit(1);
      }
      else
      {
       printf("call VirtualAlloc LastError=%d\n", GetLastError());
       strcpy((char*)lpvBase, "I am a boy!");
       VirtualFree(lpvBase, 0, MEM_RELEASE);// (2)
       printf("call VirtualFree LastError=%d\n", GetLastError());
      }
      Sleep(0);
     }
    }
    　其中，VirtualFree(lpvBase, 0, MEM_RELEASE);
    　等价于
    　　　　VirtualFree(lpvBase, 0, MEM_DECOMMIT);
    　　　　VirtualFree(lpvBase, 0, MEM_RELEASE);
    　但绝不等价于
    　　　　VirtualFree(lpvBase, 0, MEM_DECOMMIT\|MEM_RELEASE);
    　也就是说，*MEM_DECOMMIT\|MEM_RELEASE组合方式是不允许的，造成虚拟内存的泄露。
    
    （二）分段方式
    　(1)预留
    　(2)提交子页
    　(3)解除提交
    　(4)释放
    
    #include <stdio.h>
    #include <windows.h>int main(int argc, char*argv[])
    {
     LPVOID lpvBase, lpPage3;      // base address of the test memory
     int i;
     for(i=0; ; i++)
     {
      lpvBase = VirtualAlloc(  // (1)
       NULL,     // system selects address
       4096*8,     // size of allocation
       MEM_RESERVE,   // allocate reserved pages
       PAGE_READWRITE);        // both read and write
      if (NULL == lpvBase )
      {
       printf("call VirtualAlloc MEM_RESERVE fail!\n");
       exit(1);
      }
      else
      {
       printf("call VirtualAlloc MEM_RESERVE, LastError=%d\n", GetLastError());
       lpPage3 = VirtualAlloc(   //(2)
        (char*)lpvBase+(4096*2), // user selects address
        4096,      // size of allocation
        MEM_COMMIT,     // allocate committed pages
        PAGE_READWRITE);   // both read and write
       if (NULL == lpPage3 )
       {
        printf("call VirtualAlloc MEM_COMMIT fail!\n");
        exit(1);
       }
       printf("call VirtualAlloc MEM_COMMIT, LastError=%d\n", GetLastError());
       strcpy((char*)lpPage3, "I am a boy!");
       VirtualFree((char*)lpvBase+(4096*2), 4096, MEM_DECOMMIT); //(3)
       printf("call VirtualFree MEM_DECOMMIT, LastError=%d\n", GetLastError());
       VirtualFree(lpvBase, 0, MEM_RELEASE); //(4)
       printf("call VirtualFree MEM_RELEASE, LastError=%d\n", GetLastError());
      }
      Sleep(0);
     }
    }