Processing WM_DEVICECHANGE messages
How a user-mode application processes WM_DEVICECHANGE
messages depends on whether the application is based purely on the Win32 API or whether it is based on the Microsoft Foundation Class (MFC) library.
Win32 applications
Win32-based applications process the messages that are sent to the application's window(s) by implementing a Window Procedure. For more information about window procedures, see the Window Procedures topic in the Microsoft Windows SDK documentation.
The following code example shows how to process WM_DEVICECHANGE
messages in a Win32-based application:
// Prototype for the function that handles the
// processing of WM_DEVICECHANGE messages.
LRESULT
OnDeviceChange(
WPARAM wParam,
LPARAM lParam
);
// The application's message processing function
// for the window that receives the WM_DEVICECHANGE
// messages.
LRESULT CALLBACK
WindowProc(
HWND hWnd,
UINT uMsg,
WPARAM wParam,
LPARAM lParam
)
{
switch (uMsg)
{
.
. // Cases for other messages
.
// Device change message
case WM_DEVICECHANGE:
OnDeviceChange(wParam, lParam);
break;
.
. // Cases for other messages
.
// Catchall for all messages that are
// not handled by the application.
default:
return DefWindowProc(
hWnd,
uMsg,
wParam,
lParam
);
}
return 0;
}
// The function that handles the processing
// of WM_DEVICECHANGE messages.
LRESULT
OnDeviceChange(
WPARAM wParam,
LPARAM lParam
)
{
PDEV_BROADCAST_HDR devHdr;
PDEV_BROADCAST_DEVICEINTERFACE devInterface;
HANDLE ProcessHandle;
DWORD_PTR ProcessAffinityMask;
DWORD_PTR SystemAffinityMask;
DWORD_PTR ChangedAffinityMask;
MEMORYSTATUSEX MemoryStatus;
// Check whether the message is a device arrival message
if (wParam == DBT_DEVICEARRIVAL)
{
// Get a pointer to the structure header
devHdr = (PDEV_BROADCAST_HDR)lParam;
// Check whether the message is about a device interface
if (devHdr->dbch_devicetype == DBT_DEVTYP_DEVICEINTERFACE)
{
// Get a pointer to the device interface structure
devInterface = (PDEV_BROADCAST_INTERFACE)devHdr;
// Check whether this is a message about a processor
if (IsEqualGUID(
devInterface->dbcc_classguid,
GUID_DEVICE_PROCESSOR
))
{
// Get a handle to the current process
ProcessHandle =
GetCurrentProcess();
// Get the current process and system affinity masks
GetProcessAffinityMask(
ProcessHandle,
&ProcessAffinityMask,
&SystemAffinityMask
);
// Get a mask of any change to the set of processors
ChangedAffinityMask =
ProcessAffinityMask ^ SystemAffinityMask;
// Perform any per processor memory allocation
// for any new processors
...
// Set the process affinity mask to use all the
// active processors in the hardware partition.
SetProcessAffinityMask(
ProcessHandle,
SystemAffinityMask
);
// Adjust the number of threads in any thread
// pools as needed for optimal performance.
...
}
// Check whether this is a message about memory
else if (IsEqualGUID(
devInterface->dbcc_classguid,
GUID_DEVICE_MEMORY
))
{
// Get the current memory status
GlobalMemoryStatusEx(&MemoryStatus);
// Note: MemoryStatus.ullTotalPhys contains
// the amount of physical memory in the
// hardware partition.
// Adjust the memory buffer allocations
// as needed for optimal performance.
...
}
}
}
return 0;
}
Microsoft Foundation Class (MFC) applications
The MFC framework processes the messages that are sent to an MFC-based application's window(s). An MFC-based application must implement an CWnd::OnDeviceChange member function for the application's window class that receives the WM_DEVICECHANGE
messages.
The following code example shows how to implement an OnDeviceChange member function in an MFC-based application:
afx_msg BOOL
CAppWnd::OnDeviceChange(
UINT nEventType,
DWORD_PTR dwData
)
{
PDEV_BROADCAST_HDR devHdr;
PDEV_BROADCAST_DEVICEINTERFACE devInterface;
HANDLE ProcessHandle;
DWORD_PTR ProcessAffinityMask;
DWORD_PTR SystemAffinityMask;
DWORD_PTR ChangedAffinityMask;
MEMORYSTATUSEX MemoryStatus;
if (nEventType == DBT_DEVICEARRIVAL)
{
devHdr = (PDEV_BROADCAST_HDR)dwData;
if (devHdr->dbch_devicetype == DBT_DEVTYP_DEVICEINTERFACE)
{
devInterface = (PDEV_BROADCAST_INTERFACE)devHdr;
if (IsEqualGUID(
devInterface->dbcc_classguid,
GUID_DEVICE_PROCESSOR
))
{
// Get a handle to the current process
ProcessHandle =
GetCurrentProcess();
// Get the current process and system affinity masks
GetProcessAffinityMask(
ProcessHandle,
&ProcessAffinityMask,
&SystemAffinityMask
);
// Get a mask of any change to the set of processors
ChangedAffinityMask =
ProcessAffinityMask ^ SystemAffinityMask;
// Perform any per processor memory allocation
// for the new processors
...
// Set the process affinity mask to use all the
// active processors in the hardware partition.
SetProcessAffinityMask(
ProcessHandle,
SystemAffinityMask
);
// Adjust the number of threads in any thread
// pools as needed for optimal performance.
...
}
else if (IsEqualGUID(
devInterface->dbcc_classguid,
GUID_DEVICE_MEMORY
))
{
// Get the current memory status
GlobalMemoryStatusEx(&MemoryStatus);
// Note: MemoryStatus.ullTotalPhys contains
// the amount of physical memory in the
// hardware partition.
// Adjust the memory buffer allocations
// as needed for optimal performance.
...
}
}
}
return TRUE;
}
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