PRB: GlobalAlloc() Pagelocks Blocks on Win32s

MORE INFORMATION

A Windows-based application will not fix or page-lock memory even when specifically using the GMEM_FIXED flag. This behavior is unique to Windows version 3.1; using GlobalAlloc() with GMEM_FIXED to allocate fixed and page- locked memory must be done in a DLL.

In Windows 3.1, the GMEM_FIXED flag is defined as 0x0000. Using GMEM_ZEROINIT without GMEM_MOVEABLE will command GlobalAlloc() to allocate using GMEM_FIXED by default. Since Win32s passes all GlobalAlloc() calls to the Windows 3.1 GlobalAlloc() by a DLL, GlobalAlloc() called from either a Win32 application or a Win32 DLL will allocate the block fixed and page- locked unless the GMEM_MOVEABLE flag is specified.

The following code illustrates this case:

   {
   HGLOBAL hMem;

   // allocate a block from the global heap

   hMem = GlobalAlloc(GMEM_ZEROINIT, 512);

     .
     .
     .

   }
				

Although this source code is compatible between applications for Windows 3.1 and applications for Windows NT running on Win32s, the result is different. A 16-bit application running on Windows 3.1 will allocate the memory as moveable and zero the contents. A Win32 application running on Win32s will allocate the memory as fixed and page-locked and zero the contents.