Re: CreateThread() question

"Jochen Kalmbach [MVP]" <>
Mon, 01 Jan 2007 22:10:01 +0100
Hi Igor!

Is h simply a pointer to id (or a value identical to id)?

A thread is uniquely identified by its ID, but there may be multiple
handles referring to the same thread (see e.g. DuplicateHandle). The ID
is valid system-wide, the handle is valid within a single process only.
The handle, in addition to referring to a thread, also carries access
control list specifying what operations you are allowed to perform on

Just a small addition: The thread ID is only unique, if the thread is
running... if the thread has terminated, the OS will "reuse" this
thread-ID after a while.

You can verify this by creating a simple test-program:

#include <windows.h>
#include <tchar.h>
#include <hash_set>

stdext::hash_set<DWORD> s_ThreadIDs;

   DWORD dwThreadId = GetCurrentThreadId();
   if (s_ThreadIDs.find(dwThreadId) != s_ThreadIDs.end())
     _tprintf(_T("Duplicate ThreadID: %d\n"), dwThreadId);
   return dwThreadId;

int _tmain()
   int i = 0;
     DWORD dwThreadID;
     HANDLE hThread = CreateThread(NULL, 0, MyThread, NULL, 0, &dwThreadID);
     if (hThread != INVALID_HANDLE_VALUE)
       Sleep(1000); // more than about 2000 threads... so be patient...
     if (( i % 100) == 0) Sleep(1);


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