process - DuplicateHandle，为什么要复制而不是仅仅获取？

Question

为什么一个进程想要从 Win32API 调用 DuplicateHandle，并从另一个进程获取它，而不是仅仅获取某个对象本身的句柄？

调用 DuplicateHandle 或其他东西有什么好处吗？

Answer 1

您可以在《Microsoft Windows 的应用程序编程》第 6.8 章中找到答案。

Gaining a Sense of One's Own Identity
Sometimes you might need to acquire a real handle to a thread instead of a pseudo-handle. By "real," I mean a handle that unambiguously identifies a unique thread. Examine the following code:

DWORD WINAPI ParentThread(PVOID pvParam) {
   HANDLE hThreadParent = GetCurrentThread();
   CreateThread(NULL, 0, ChildThread, (PVOID) hThreadParent, 0, NULL);
   // Function continues...
}

DWORD WINAPI ChildThread(PVOID pvParam) {
   HANDLE hThreadParent = (HANDLE) pvParam;
   FILETIME ftCreationTime, ftExitTime, ftKernelTime, ftUserTime;
   GetThreadTimes(hThreadParent,
      &ftCreationTime, &ftExitTime, &ftKernelTime, &ftUserTime);
   // Function continues...
}

Can you see the problem with this code fragment? The idea is to have the parent thread pass to the child thread a thread handle that identifies the parent thread. However, the parent thread passes a pseudo-handle, not a real handle. When the child thread begins executing, it passes the pseudo-handle to the GetThreadTimes function, which causes the child thread to get its own CPU times, not the parent thread's CPU times. This happens because a thread pseudo-handle is a handle to the current thread— that is, a handle to whichever thread is making the function call.

To fix this code, we must turn the pseudo-handle into a real handle. The DuplicateHandle function (discussed in Chapter 3) can do this transformation