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DisableThreadLibraryCalls function

Disables the DLL_THREAD_ATTACH and DLL_THREAD_DETACH notifications for the specified dynamic-link library (DLL). This can reduce the size of the working set for some applications.


BOOL WINAPI DisableThreadLibraryCalls(
  _In_ HMODULE hModule


hModule [in]

A handle to the DLL module for which the DLL_THREAD_ATTACH and DLL_THREAD_DETACH notifications are to be disabled. The LoadLibrary, LoadLibraryEx, or GetModuleHandle function returns this handle. Note that you cannot call GetModuleHandle with NULL because this returns the base address of the executable image, not the DLL image.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. The DisableThreadLibraryCalls function fails if the DLL specified by hModule has active static thread local storage, or if hModule is an invalid module handle. To get extended error information, call GetLastError.


The DisableThreadLibraryCalls function lets a DLL disable the DLL_THREAD_ATTACH and DLL_THREAD_DETACH notification calls. This can be a useful optimization for multithreaded applications that have many DLLs, frequently create and delete threads, and whose DLLs do not need these thread-level notifications of attachment/detachment. A remote procedure call (RPC) server application is an example of such an application. In these sorts of applications, DLL initialization routines often remain in memory to service DLL_THREAD_ATTACH and DLL_THREAD_DETACH notifications. By disabling the notifications, the DLL initialization code is not paged in because a thread is created or deleted, thus reducing the size of the application's working code set. To implement the optimization, modify a DLL's DLL_PROCESS_ATTACH code to call DisableThreadLibraryCalls.

Do not call this function from a DLL that is linked to the static C run-time library (CRT). The static CRT requires DLL_THREAD_ATTACH and DLL_THREAD_DETATCH notifications to function properly.


Minimum supported client

Windows XP [desktop apps | UWP apps]

Minimum supported server

Windows Server 2003 [desktop apps | UWP apps]

Minimum supported phone

Windows Phone 8


Winbase.h (include Windows.h)





See also

Dynamic-Link Library Entry-Point Function
Dynamic-Link Library Functions