Thread: Best method to (gracefully) quit another application

Hi,

I'm writing a small launcher that is supposed to mount a virtual drive (a TrueCrypt volume), launch a menu application (called PortableApps) on that volume and then wait until this application quits. Once it does, the launcher also asks all processes launched from the volume to quit as well, waits until they do and then unmounts the volume.

Anyway, I've got this working for the most part. The only thing that doesn't really work very well is the part where it's supposed to quit the other applications. I'm using EnumProcesses/Modules and GetModuleFileNameEx to find all processes launched from the volume. Comparing the results with EnumWindows gives me the window handles of those processes and sending them a WM_CLOSE works for a couple of applications. Others either "ignore" the message or one particular application (FreeCommander) crashes. I'm guessing this is because I send this message to all windows of a process. (Googling for something like a 'mainwindow' didn't yield any helpful results:/)

I was wondering if anybody might have a better idea on how to do this (short of using TerminateProcess ).

WM_CLOSE should work for most situations. It is the equivalent of clicking on the close button (clicking the close button sends the WM_CLOSE message to the window). You should only send WM_CLOSE to non child windows (windows without the WS_CHILD style). EnumWindows gives top level windows only, except in a few circumstances.

Calling WM_CLOSE on windows should probably be done in the order that the user would normally close the windows. For example, if there's a modal dialog active for an application, WM_CLOSE should be sent to that window first (as the user normally cannot click the close button while a modal dialog is active, so sending WM_CLOSE to it may yield unexpected results). That's not to say that most programs will have issues with it.

EnumThreadWindows can be used to determine what windows belong to a specific thread (message pump).

The nice thing about WM_CLOSE is that if you have any unsaved documents, most applications will prompt you to save them, as there should be no difference between using that and the user clicking the close button or using Alt-F4. All other methods will yield undesired side effects (at least ones that do not use WM_CLOSE or something that triggers a WM_CLOSE to be sent).

I downloaded FreeCommander to play with it, and I noticed that there were several hidden top-level windows associated with it. I don't know if you're using Visual Studio, but there's a program that comes with it called Spy++ which is quite useful for determining what windows are associated with a process, each window style, etc. The main issue though is a window that not technically hidden (but off the screen) that has a class name of "TApplication". It's sending a WM_CLOSE to this window that is causing the issue. Unfortunately, I can't think of any very good way of detecting this case, other than by it's class name (this is a common feature of Delphi and C++ VCL applications, I believe). The other windows can be filtered out by making sure that the WS_VISIBLE style is set before sending it a WM_CLOSE.

Originally Posted by tjb

I downloaded FreeCommander to play with it, and I noticed that there were several hidden top-level windows associated with it. I don't know if you're using Visual Studio, but there's a program that comes with it called Spy++ which is quite useful for determining what windows are associated with a process, each window style, etc.

Thanks for researching that. I'm using a free IDE called CodeBlocks, but I think I could get a free students license of VS, if only for Spy, which sounds like it would help quite a bit.

Originally Posted by tjb

The main issue though is a window that not technically hidden (but off the screen) that has a class name of "TApplication". It's sending a WM_CLOSE to this window that is causing the issue.

Right, I remember that. I think it's some sort of project container class that 'uses' (=includes) all forms and runs the main loop.

Originally Posted by tjb

Unfortunately, I can't think of any very good way of detecting this case, other than by it's class name (this is a common feature of Delphi and C++ VCL applications, I believe). The other windows can be filtered out by making sure that the WS_VISIBLE style is set before sending it a WM_CLOSE.

I'll try that, thanks tjb.