DWM Leaks Memory When No Monitor Connected Windows 8 - windows

Question

Simply, if no monitor connected and you are doing some "windows" operation on windows 8 embedded, dwm.exe starts allocating memory and never stops.
to regenerate and show you all the problem, i have written an application which is doing "Create a new Form and show it, if there is one created close it first"
public partial class PopupWindows : Form
{
private Timer _t;
private Form _form;
public PopupWindows()
{
InitializeComponent();
this.Size = new Size(500, 500);
}
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
_t = new Timer();
_t.Tick += (o, ea) =>
{
_form?.Close();
(_form = new Form() { Size = this.Size }).Show();
};
_t.Interval = 1000;
_t.Enabled = true;
}
}
if you run this application and plug out the monitor, dwm start allocating pages
here is the output from pslist -m when the monitor connected
Name Pid VM WS Priv Priv Pk Faults NonP Page
dwm 840 123528 14400 11264 13044 55125 7 212
after some time but still the monitor connected
dwm 840 117144 15808 12732 13044 94051 7 200
disconnecting monitor and dwm.exe start allocating
dwm 840 214660 14444 12664 13044 137409 13 400
below is the output where you can see allocation dwm.exe doing
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 251956 14460 12740 13044 137413 16 477
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 251956 14460 12740 13044 137413 16 477
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 251956 14460 12740 13044 137413 16 477
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 252964 14460 12740 13044 137413 16 479
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 252964 14460 12740 13044 137413 16 479
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 253972 14460 12744 13044 137413 16 481
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 253972 14460 12744 13044 137413 16 481
C:\PSTools>pslist.exe -m|findstr "dwm"
dwm 840 254980 14460 12744 13044 137413 16 483
and this strange act dwm doing never stops till you connect a monitor or doing vnc connection to the computer.
after some time on operation without monitor, every os component starts to complain about memory and a blue screen of death occurs at the end.
let me show you the last one
dwm 840 807516 15624 14216 17240 147413 50 1603
here is the output showing how many minutes my popupwindows.exe running
Name Pid Pri Thd Hnd Priv CPU Time Elapsed Time
PopupWindows 2052 6 4 138 9468 0:00:00.140 0:23:07.332
as you can see, after about 20 minutes without having a monitor on the device, dwm.exe using 807516 bytes VM and 1603 pages.

Answer 1

Acting like what vnc doing (copying whole screen bitmap to application memory regularly) solved the dwm's allocation problem (which i think dwm caches its outputs but no one come and ask for the changes so it keeps all of them in the memory and never cleans).
below is the application which starts hidden and regularly copying screen image into app memory
public partial class HiddenForm : Form
{
IntPtr _this;
private System.Windows.Forms.Timer _timer;
private Bitmap _bmp = null;
public HiddenForm()
{
this.Visible = false;
this.ShowInTaskbar = false;
this.FormBorderStyle = FormBorderStyle.None;
this.HandleCreated += (s, e) => _this = this.Handle;
this.Load += (s, e) => this.Size = new Size(0, 0);
CreateHandle();
CreateControl();
_timer = new System.Windows.Forms.Timer();
_timer.Tick += _timer_Tick;
_timer.Interval = 2000;
_timer.Start();
}
private void _timer_Tick(object sender, EventArgs e)
{
if (Screen.PrimaryScreen == null)
return;
if (_bmp == null)
{
using (Graphics g = CreateGraphics())
{
_bmp = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, g);
}
}
using (Graphics grp = Graphics.FromImage(_bmp))
{
grp.CopyFromScreen(0, 0, 0, 0, _bmp.Size);
}
}
}
here is the output after starting my app
Name Pid VM WS Priv Priv Pk Faults NonP Page
dwm 832 117876 20188 19624 35004 184497 7 185
killing my app with pskill waiting a while
dwm 832 182388 20264 19852 35004 421343 11 317
it starts increasing to re check our app i started it again by typing
C:\HiddenForm.exe
and dwm.exe memory allocation magically downed.
dwm 832 126384 27900 27364 35144 556729 7 187