I'm working on something that's basically a task manager. I have a working prototype but now I'd like to be able to show applications that are not responsive.
Are there APIs that can tell me whether this is the case under Window, macOS, Linux? I need to do this without the cooperation of the processes, so I can't just send a custom message and wait for a response.
Preferably C, but I can work with Obj-C & co.
Related
I'm trying to create a multithreaded opengl application with libx11 - with one separate thread per window, and one manager thread.
I have an event loop in the manager thread:
while(true)
while(XQLength(mPlatformData->display)){
XNextEvent(mPlatformData->display, &event);
std::cout << "event" << std::endl;
}
}
This is a great event loop for single threaded applications, but with this multithreaded setup strange things happen.
When I'm creating a window, I need to disable the event queue, or GLXMakeCurrent will just hang - my entire thread stops, and does nothing.
I can't find much information about multithreaded X11 applications on the net, should I handle my events differently?
It is known that Xlib has several unfixable runtime issues that manifest in concurent access situations. I'm guessing you're running into exactly one of those.
This is one among the reasons why Xcb was created in the first place: Fix the problems of Xlib. GLX is specified against Xlib so this might seem like a show stopper when it comes to OpenGL. However there is a Xlib wrapping around Xcb and one can safely use that to interface with GLX and still use Xcb for the rest of the program: http://xcb.freedesktop.org/opengl/
I see two possible solutions:
Put a XLockDisplay/Mutex around XNextEvent and the GLX calls each; you don't have to lock for ordinary OpenGL, just the functions prefixed glX....
Use Xcb to get runtime correct behaviour and follow the guide I linked above to make it work with OpenGL/GLX.
As eile said you should check that you use XInitThreads.
I was able to get some good results from it when i used a background thread to do the window drawings of an animation. There seems to be no real problem if you stick to drawing code.
If you need more then that and because you are using low level libX11 the best is just to open multiple X11 connections and use one connection per toplevel window. I did this 10 years ago when i played with developing a BeOS cross platform toolkit and when everything was in a worse state then it is now.
You can use this even for event handling and child windows of a toplevel. But this needs some very tricky code for the XEvent masks.
What are you doing in your render threads? In any case, if you share a Display* connection across different threads you have to call XInitThreads.
I've made good experiences with one Display connection per thread. Use XSelectInput to get events on your main thread. Window IDs are shareable across different Display* connections.
Using the lisp implementation of the X11 protocol, get-overlay-window freezes when no compositor is running. If I kill the lisp process, the xid is printed out.
This also freezes my lisp window manager running in another lisp thread, though same process. Basically X acts like it's been grabbed, so thank god for ctrl-alt-f1.
Some previous questions about composite show others running into similar problems when no compositor is running.
I'm guessing that maybe the server is waiting for some sort of out of protocol authorization or something? Or something particular sequence of events has to be completed?
Having access to the overlay window when another compositor is active isn't helpful for writing a compositor!
Apparently I had a reading comprehension fail with the protocol description, or they a writing fail.
Asking composite to redirect windows automatically ensures the windows contents get drawn. It does not ensure they get drawn to the overlay! Nor does the overlay appear to be transparent. So even with setting all windows to be automatically updated, when the overlay window gets mapped by the call to get its XID it blocks you from seeing any other updates to the screen and blocks all input.
Making the overlay in a sense not very useful. Or the request to have automatic updates for redirected windows not useful. Either way, seems will have to paint every single pixel even of the windows we're not interested in.
Maybe it's just a driver thing?
I've been looking at Windows's File System Filter Drivers. I started with this "FsFilter" example:
http://www.codeproject.com/Articles/43586/File-System-Filter-Driver-Tutorial
With effort, I managed to get it built and signed in versions that work on everything from 64-bit Win8 to 32-bit WinXP. (Well, as long as I run Bcdedit.exe -set TESTSIGNING ON to allow it to accept my test certificate, since I didn't pay Microsoft $250 to sign my .SYS file. :-/)
Now I want to modify FsFilter. I'd like write accesses to certain types of files to be trapped by the filter. I then want the user to receive a dialog box, in which they can either allow the access or deny it.
Perhaps obviously...the kernel-mode code cannot display the UI. It will have to signal some user mode process, which will (after an arbitrarily latent period of time) signal back the user's wish to the driver. I've looked a bit over
User-Mode Interactions: Guidelines for Kernel-Mode Drivers (here's Google's Cache as HTML, instead of .DOC)
I don't know what the best way to attack this is. The only example I've yet found to study is SysInternals FileMon. The driver it installs gathers data in a buffer, which is periodically requested by the .EXE according to a WM_TIMER loop:
// Have driver fill Stats buffer with information
if ( ! DeviceIoControl( SysHandle, IOCTL_FILEMON_GETSTATS,
NULL, 0, &Stats, sizeof Stats,
&StatsLen, NULL ) )
{
Abort( hWnd, _T("Couldn't access device driver"), GetLastError() );
return TRUE;
}
Should I use a similar technique? Perhaps the filter driver, upon receiving a request it wants to check, could place a record to track the request in a buffer that would contain two HEVENTs. It would then WaitForMultipleObjects on these two HEVENTs, which represent a signaled "YES" or "NO" from user mode on whether to allow access.
Periodically the monitor process (running in user mode) will poll the driver from another thread using a custom IOCTL. The filter driver would return the request information... as well as the two HEVENTs that request is waiting on. The monitor would wait for the user's feedback, and when available signal the appropriate event.
I could also invert this model. The user mode code could use a custom IOCTL to pass in data... such as HEVENTs which could be signaled by the driver, and just implement some kind of safe protocol. This would eliminate the need for polling.
Basically just looking for guidance on method, or a working example on the web! I'd also be interested to know what the mechanics would be on an asynchronous file access. I assume there's a way so a client making an async call that is being checked could keep running and only be held up when they waited on the request to finish...?
(Note: Along the way of getting the filters built and debugged, I learned there are some more modern techniques via "miniFilters"--which are part of something called the Filter Manager Model. But for the moment, I'm not that concerned as long as the legacy model is supported. It looks rather similar anyway.)
You (a.k.a. I) have pretty much enumerated the possibilities. Either poll the way FileMon does, or pass an event. Passing the event is probably a bit more error prone, and if you aren't a threading guru then there's probably more chance for error. But if you tend to make lots of mistakes then device drivers may not be for you...skydiving might be a poor choice too.
I'll offer taking a look at this project, but please note the disclaimers in the README. (It is only a test and investigation):
https://github.com/hostilefork/CloneLocker
And yes, to the extent that Microsoft and their driver model is to be something one worries about, miniFilters are the better choice these days.
I am using C language and Linux as my programming platform.
I am developing a user-space application that runs in a background, like a daemon. And my problem is, I want another user-space application to communicate with this daemon.
I know that I have to use Interprocess Communication method but I don't know what is the correct implementation.
But using IPC in my communication implementation is my other option. Actually I just want to change the attribute of my daemon by using another application. Please see below a senario:
My daemon runs in a background.
Then some application will control the properties of a daemon, like sleeping delay time.
My first option is by accessing a file with the values of the properties. So that my deamon will poll that values. While the other application will change that values.
I am not sure the efficiency of my options. Please advice.
THanks.
Updating the config file and sending a signal to cause re-read is a standard practise, cheap and easy.
You're looking for D-Bus. Store the initial values in a file, then listen over D-Bus for requests to change it.
Unix domain sockets are a simple IPC method.
If I were you, I'd forego IPC completely and instead have the daemon monitor a config file for changes. IPC is only really needed if you're going to be sending thousands of messages per second and the overhead would get intolerable.
inotify is an option for file monitoring.
I'd make the daemon listen on a pipe/fifo if it's simple enough that you only need to read a couple of bytes fed in from another program. Otherwise a local domain socket is nice to run a simple protocol over.
Using C winapi, how can you capture receieved data from a commport that is open exclusively by another program.
I know there are programs that do this, but I want to code my own monitoring software for a specific purpose and was wondering how is it done?
You can do this using API hooking see here: http://www.codeproject.com/KB/system/hooksys.aspx for details. Basically you could load the target process, inject some code into the target process to hook the API that you're interested in and then use an IPC mechanism to transfer the data from your hooks to your analysis program.
This is how my program that can control the values returned by GetTickCount() in another program works (see here http://www.lenholgate.com/blog/2006/04/tickshifter-v02.html)