TL;DR - How does the Spy++ tool really construct its process list?
Stage
We have an MFC desktop application (running on Windows XP) that is hanging in that it doesn't react to any user input anymore. It is redrawn when switching to it via alt-tab however. (It does receive WM_SETFOCUS, WM_ACTIVATE, etc. It apparently does not receive any mouse or keyboard messages.)
Since the app is hanging in some limbo, we pulled a few process dumps, but these were of little help so far. Enter:
Spy++
We used Spy++ to find the information I gave above about the window messages this application seems to be processing. We did this by Opening the Windows View and selecting our application Window and in the Messages properties selected Windows of same process and Messages to View : Select All.
However we first tried to view all messages of this process by opening the Processes View of Spy++ and our application is not shown in this process list. Cross checking on another PC where the app is running normally, the process is also normally shown in the processes list of Spy++.
Can anything about the misbehaving app be inferred from the fact that the process is not shown in Spy++'s Process View, but the main window of the app is shown in the Windows View. Why would a process with a main window that is visible not be shown in Spy++'s Processes View?
The process is listed in Task Manager and in the Attach Process Window of Visual Studio 2005. So these tools apparently use a different method to list processes than Spy++ ... ?
The system where the app is currently hanging is a Windows XP SP2 system and we've used the Spy++ Utility that comes with Visual Studio 2005.
The behavior does recur occasionally, but only after the App has been running for several days!
Running Vista or later? Your process is probably elevated and Spy++ is not. Newer versions of Spy++ require elevation. So, try elevating Spy++ explicitly and see if that helps.
Yes, of course things can be inferred from this. Don't take anything I say too seriously in this context, I'd have to go look at the code. But I believe that Spy goes off and looks at the EnumProcesses API. (http://msdn.microsoft.com/en-us/library/ms682629.aspx)
So, if your process isn't showing up there... hrm.
But, what is different between the system where it's working and the one where it's not?
Spy++ requires the following two values in the registry to be disabled (0) to display the processes/threads list AT ALL:
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Perflib
HKLM\System\CurrentControlSet\Services\PerfProc\Performance
Disable Performance Counters -> either 0 or not present
Was going insane trying to find out why it refused to display them. It's some kind of bad joke - this debugger requires itself a debugger to get it working! Not that WinDBG would display any meaningful info, MS doesn't even provide a symbol file on their symbol server, pfft.
Anyway, maybe it doesn't display processes that have their performance counters disabled, because I think, this can be set on individual basis, at least for services, like:
HKLM\SYSTEM\CurrentControlSet\Services\.NET CLR Networking\Performance
Disable Performance Counters
So it's basically always a value of the "Performance" subkey. All this stuff is undocumented, it makes use of advapi32.dll functions like "PerfRegQueryValue" and "PerfRegQueryInfoKey"... don't ask me.
Related
On Microsoft Windows (8), I would like to start a process, and prevent it from showing any windows at all. Alternatively, to force-close any windows that are shown. Is there a way to do this?
My application is this: I'm running an automated (nunit) test suite on my continuous integration (teamcity) server. The code under test is also used by an interactive application. Developers occasionally slip in a dialog with a user prompt, without realising what they are doing. This causes the CI process to stop, waiting for user input which never comes. I'd like to be able to dismiss any dialog that appears, or prevent them from being shown.
Even better would be to force an exception at this point, so that the test would also fail.
In my case, this is a C# application, and the dialogs shown are Windows Forms or WPF dialogs.
I did find a couple of similar questions. However each turned out to be solving a slightly different problem.
Stop a process from showing a window from C# (solves a different problem)
Preventing blocking dialogs/message boxes/hanging GUI from non-interactive processes on Windows? (promising solution but C++-specific)
Prevent child process from creating visible windows? (solves a different problem)
Have you considered asking your development team to have a "no dialog" mode of the app for testing purposes? Perhaps if you stopped referring to them as (!!*&%) they would be more inclined to partner with you. ;) Afterall, you do work at the same company on the same product :)
In any case, without a dev-specific solution, consider having a another app (process or thread) that continually sleeps for a few seconds, wakes up and looks for a modal dialog in your application. You can use APIs such as FindWindow to identify when a modal dialog has popped up. (Use Spy++ to get the class name for windows created by MessageBox and CreateDialog APIs).
When my program is paused in Visual Studios 2010 during debugging, like from reaching a break point and me doing a manual step through, the program window becomes impossible to view.
It is a GUI window not a console window, which I run simultaneously with my program and am still able to view. The window seems to be open it's just that when I click its icon on the taskbar it doesn't come to the front of all the other windows. When I minimize all the windows in front of it, I see the outline of the window but it is either blacked out or showing the remnants of previously expanded windows.
I've noticed this with using Visual Studio's before (various versions of it), and after trying other IDE's that didn't have this behavior I notice it more. It would be really helpful to view the program's change's as I step through the program. Anyone know how I can do this?
I searched a long while and couldn't find a single reference to this matter.
The reason the window doesn't display is that the window paint message won't be processed if the main thread has been paused. Which other IDEs let you do this? I haven't come across any native code debuggers that do this on Windows.
If you are stepping through code that is run by the main thread, then the main thread can't simultaniously poll the message pump, which is needed for the GUI to work.
If you debug a different thread, the GUI will work while you are debugging.
I have been working on windows automation and monitoring.
What exactly happens when I lock the screen of a windows machine?
I am working with Windows 7 at the moment, are there big differences to the behavior if I switch to Vista or the server versions?
Is there still a desktop that can be accessed via api's?
I know that i can still send key strokes and mouse clicks to specific windows (via ControlSend and ControlClick), but there seems to be no "desktop" itself.
Could someone shed some light on this whole thing or point me at a readable source where I could get an overview over the topic?
Basically what happens is that Windows switches to the secure desktop, makes it the current one, so input is now associated with it.
The old desktop remains where it was: all the HWNDs on the desktop are still there, and any thread attached to that desktop can still access those HWNDs, get their location, and so on. You can still send messages to windows on this desktop, so long as the thread sending the message is also on that desktop.
However, since the desktop is now inactive, it cannot receive input. GetForegroundWindow will return NULL (IIRC), and you can't use SendInput any longer, since input now belongs to [a thread on] a different desktop; no controls on that inactive desktop can receive focus.
Note that sending keypress messages to a control that doesn't have focus can sometimes cause unexpected behavior, since the app or control generally never expects to receive keyboard input without getting the focus first. (This can be problematic for controls that set up some sort of input context in WM_SETFOCUS and clear it up in WM_KILLFOCUS, for example.)
In short, the UI is still there: you can do certain queries against it, but you can no longer automate it as you could on a regular desktop by sending input, and some other functions that relate to focus or input may fail.
I'm not super familiar with AutoHotKey, but the name and description of functionality suggests that it's heavily reliant on the underlying Win32 SendInput API. This won't work at all for keyboard input when a desktop is inactive.
For a reasonable overview of how desktops work and how they relate to winstations, the locked desktop, and so on, check out the Desktop article on MSDN.
One issue that I've run into in the past with desktops and automation is: how to I leave a long-running test that's using some form of user input automation (mouse, keyboard simulation), but still lock my PC so that someone can't just walk by and interfere with it. Once you lock the PC, the desktop is inactive, and so the automation stops working. A similar issue happens if the screensaver kicks in: the desktop switches, and the automation fails.
One solution is to use two PCs: let's call them Main and Test: from Main, open a remote terminal services client onto the Test machine, and then run the automated test on the test machine, but from a terminal services client window on the Main machine. Now the cool part: you can minimize that TSC window, or even lock the Main machine (or let the screensaver kick in), and that virtual session will continue working, thinking that it is still active - it's just that nobody is paying it any attention. This is one way to create a "connected" session with an active desktop, but one that no-one can interfere with, because it's protected behind the locked desktop of the Main machine.
I don't know the details, but I believe the lock screen constitutes a separate "desktop" and maybe also a separate "window station" (as I understand it a window station is merely a container for desktops). The MSDN section on window stations should hopefully be useful: http://msdn.microsoft.com/en-us/library/windows/desktop/ms687098%28v=vs.85%29.aspx
In order to access a desktop, you will need to use the regular windows api's from a thread that is on that desktop. SetThreadDesktop would probably be the easiest way to do that in C, as long as the desktop isn't on a different window station.
Unfortunately, this is already difficult for a regular privileged application, and using AutoHotkey complicates it even more. Since you don't have control over threads or over process initialization, you will probably have to create a new process in the other desktop (you can do this using the CreateProcess API, which appears to have a wrapper available for AHK to which you can supply a desktop name: http://www.autohotkey.com/forum/topic1952.html). Your process will need special privileges to do this; I'm not sure that even running as Administrator is enough.
In Visual Studio's Attach to Process dialog, one of the columns in the Available Processes list is "Title", which lists the title of the topmost window owned by each process.
We spawn multiple instances of several server processes in order to compartmentalize the work. For these console processes, the Title field is blank, so currently we have to look up the process id in our management tool in order to find the correct process.
In order to streamline the debugging process, I would love to be able to use the Title field to directly determine which process I want.
SetConsoleTitle does not do the trick, nor SetWindowText with a NULL hWnd. To the best of my knowledge, a console application does not intrinsically own any window handles that we could pass to SetWindowText. We don't want to create any visible windows for these server processes.
Any suggestions for a reasonable way to trick Visual Studio into displaying some useful information here?
I think you might be out of luck. The console window does not belong to the console process, but instead belongs to a system process (conhost.exe on win7 and maybe vista, csrss.exe before that) so if Visual Studio is just looking for a processes top level windows it won't find the console window. Probing consoles out of proc is not supported as far as I know, so there is probably no sensible way for visual studio to see the title of the console windows you have.
One possible solution might be to create a top level window in your console process as a debugging aid. You might want to conditionally compile it, so it is only available when you're debugging though. Just create an additional thread which pumps messages, and create a top level window. If you set the right styles the window will be invisible. You might not want to ship with the window in the code because in long running server code, windows always increase your attack surface, even if only a little bit.
This is probably not very helpful, but it is worth mentioning that on windows the preferred way of portioning up work would be to use threads rather than multiple processes. A process is an expensive object, and threads are much cheaper in terms of system resources as well as being easier to debug.
I am debugging an application which, in its message loop, calls IsDialogMessage(). Occasionally, IsDialogMessage() never returns (where never is an interval greater than 1 hour). Based on the symbols for user32.dll available from Microsoft's symbol server, it appears to be stuck in GetNextDlgGroupItem() (or an internal variant of the same), iterating over some set of windows.
The application is multithreaded and frequently receives notification of external events, which arrive as DCOM calls. I suspect that such a call is handled incorrectly in a way that corrupts some window state. If I can learn what sort of state corruption might cause an infinite loop in IsDialogMessage(), I think I will be more easily able to identify the source of the corruption.
I know this is old, but answering for posterity since no one here mentioned it.
More than likely what is going on is trouble with the windows manager determining where to forward a message. If you have a hierarchy of windows, as you probably do, then you need to ensure that non-top-level windows that contain controls themselves must have the WS_EX_CONTROLPARENT style set. If it is a dialog, you use the DS_CONTROL style. The presence of these flags modify the behavior of IsDialogMessage; they identify a window as having its own controls which can receive focus and handle tab order, etc, rather than just being a control itself.
For example, if you have a main frame window, which has a child window with WS_EX_CONTROLPARENT, which has a child window without WS_EX_CONTROLPARENT, which has a child window that has focus, and you hit TAB, you will likely encounter an infinite loop at the same place you mention.
Setting the second child's extended style to include WS_EX_CONTROLPARENT will resolve the issue.
Are you maybe disabling controls (using ::EnableWindow()) without checking first whether that control has the focus? If yes, then the focus gets lost and GetNextDlgGroupItem() gets confused.
Another reason this can happen is if you reparent a modeless dialog. At least this can happen with wxWidgets...
I've made some investigation, trying to answer this question. But only in situation, when parent window is in native MFC project and child is a managed C# Windows Forms. If you have such situation, then you may try 3 resolutions:
Run MFC dialog message loop on Windows Forms side. Here is more info: Integrate Windows Forms Into Your MFC Applications Through C++ Interop
Create 2 threads: one for Windows Forms dialog and one for native dialog. Here you can create dialog in Windows Forms, then with SetParent() set it's parent to native dialog. But be ware: if you add TabControl to Windows Forms, than hang with "IsDialogMessage() never return" will occur.
Make a wrapper for Windows Forms dialog to use in native project. For ex., wrapper may be WPF, see here: Windows Form as child window of an unmanaged app
I've taken information mostly from: http://msdn.microsoft.com/en-us/library/ms229600.aspx
And the temporary cure can be to change focus behavior. For example, disable them, or SetFocus() to parent or child windows only. But I strongly recommend to investigate the real reason, why IsDialogMessage() never return in your case.