I'm quite confused as to what should and should not be done in QApplication::commitData. The name implies that I should just store the state, and the docs say it should not close the application. However, the default implementation indeed closes all windows thereby closing the application. Also, if this is not the way to detect windows shutdown, I don't see any other way to tell that windows is indeed being shutdown.
There is also the related saveState. The function name means about the same and the documentation is also quite similar.
How am I supposed to properly detect when the system is being shutdown and both save my state and close my application? Is commitData indeed the correct way and just suffering from a very poor name and bad documentation?
In my practice to detect an application shutdown I usually connect to the slot void QCoreApplication::aboutToQuit (). As it says in the docu:
The signal is particularly useful if your application has to do some last-second cleanup. Note that no user interaction is possible in this state.
So far so good this has worked for me properly
commitData() and saveState() may seem redundant.
But the documentation
says
Futhermore, most session managers will very likely request a saved state immediately after the application has been started. This permits the session manager to learn about the application's restart policy.
Maybe that explains why the notion of 'data' and 'state' are separated. During that initial call, it would not be user friendly to interact with the user.
The default response to shutdown the application seems like a good design, because if you don't reimplement, then the safest thing to do is to close the app (as if the user had chosen the Quit action), which should also save the user's data.
Is the OS shutting down, or only the session? As far as your app should be concerned, it is only the session (since technically, the user could be logging off and the OS continues to run.) And the user might consider the app to be not 'shut down', just 'paused with data safed.'
Also consider mobile platforms like iOS, where an application seeming runs forever.
Related
I've got a C++ app (Qt-based) running on MacOS (10.10 and newer), and I'd like it to modify its behavior slightly when it is running under MacOS's app-nap mode. (In particular, there are some periodic network queries it does in order to update status indicators in its GUI, but if the application is napping I'd prefer that it stop doing them until after it has woken up from its nap).
If I had a function like this:
bool IsThisProcessNapping(); // returns true iff we're in app-nap mode
... I think I could implement the behavior I want, but I don't know of any such function. Does it exist under some other name?
(Note that I don't want to just disable app-nap, since I want my program to be energy-efficient if possible)
I'm not sure there's a specific answer to your question (I don't think the API you talk about actually exists).
You could start by reading Energy Efficiency Guide for Mac Apps, especially the section "Enhancing App Nap":
By default, your app becomes eligible for App Nap if it’s not actively
engaged with the user and hasn’t updated a visible window for some
length of time. However, your app knows the most about the importance
of its activity, and shouldn’t rely on App Nap to put it into an idle
state. The most effective way to enhance App Nap is for your app to
listen for notifications that it’s no longer in active use and to
suspend energy-intensive work as quickly as possible
Given the scenario you describe (pausing network requests to update status indicators), check out Notify Your App When Visibility Changes.
It has examples of the application delegate methods applicationDidChangeOcclusionState: and windowDidChangeOcclusionState:. When your app or the relevant window is occluded, you could pause your network activity, and resume it when the occlusion state goes back to visible.
The guide mentioned above also links to similar documentation for checking the active state of your app.
If your app is not visible, and not active, it's a candidate for App Nap. At that point, what difference does it make in your case if the app is actually napping yet? If your aim is to be energy efficient, pause your network activity once the app is not visible - since no-one can see your status indicator anyway!
I'm developing an updater for my application in Qt, primarily to get to know the framework (I realize there are multiple ready-made solutions available, that's not relevant here). It is a basic GUI application using a QMainWindow subclass for its main window and an MyAppUpdater class to perform the actual program logic.
The update information (version, changelog, files to be downloaded) is stored on my server as an XML file. The first thing the updater should do after it sets up the UI is query that server, get the XML file, parse it and display info to the user. Here's where I have a problem though; coming from a procedural/C background, I'd initiate a synchronous download, set a timeout of maybe 3 seconds, then see what happens - if I manage to download the file correctly, I'll parse it and carry on, otherwise display an error.
However, seeing how inconvenient something like that is to implement in Qt, I've come to believe that its network classes are designed in a different way, with a different approach in mind.
I was thinking about initiating an asynchronous download in, say, InitVersionInfoDownload, and then connecting QNetworkReply's finished signal to a slot called VersionInfoDownloadComplete, or something along these lines. I'd also need a timer somewhere to implement timeout checks - if the slot is not invoked after say 3 seconds, the update should be aborted. However, this approach seems overly complicated and in general inadequate to the situation; I cannot proceed without retrieving this file from the server, or indeed do anything while waiting for it to be downloaded, so an asynchronous approach seems inappropriate in general.
Am I mistaken about that, or is there a better way?
TL;DR: It's the wrong approach in any GUI application.
how inconvenient something like that is to implement in Qt
It's not meant to be convenient, since whenever I see a shipping product that behaves that way, I have an urge to have a stern talk with the developers. Blocking the GUI is a usability nightmare. You never want to code that way.
coming from a procedural/C background, I'd initiate a synchronous download, set a timeout of maybe 3 seconds, then see what happens
If you write any sort of machine or interface control code in C, you probably don't want it to be synchronous either. You'd set up a state machine and process everything asynchronously. When coding embedded C applications, state machines make hard things downright trivial. There are several solutions out there, QP/C would be a first class example.
was thinking about initiating an asynchronous download in, say, InitVersionInfoDownload, and then connecting QNetworkReply's finished signal to a slot called VersionInfoDownloadComplete, or something along these lines. I'd also need a timer somewhere to implement timeout checks - if the slot is not invoked after say 3 seconds, the update should be aborted. However, this approach seems overly complicated
It is trivial. You can't discuss such things without showing your code: perhaps you've implemented it in some horribly verbose manner. When done correctly, it's supposed to look lean and sweet. For some inspiration, see this answer.
I cannot proceed without retrieving this file from the server, or indeed do anything while waiting for it to be downloaded
That's patently false. Your user might wish to cancel the update and exit your application, or resize its window, or minimize/maximize it, or check the existing version, or the OS might require a window repaint, or ...
Remember: Your user and the environment are in control. An application unresponsive by design is not only horrible user experience, but also makes your code harder to comprehend and test. Pseudo-synchronous spaghetti gets out of hand real quick. With async design, it's trivial to use signal spy or other products to introspect what the application is doing, where it's stuck, etc.
Is there some type of notifications that iOS emits when app get force quited?
By force quite i mean tapping the home button while app is in active state and then removing it from multitasking menu.
I want to be able to detect force quit, to gracefully handle everything.
We have an issue like this with one of our games and our publisher wants us to handle this.
This is not standard Cocoa App, this is game ported from PC, written mostly in C++.
This happens only on iPad Mini 2nd gen, when app is force quit-ed it will crash on next launch.
On other devices, when app is activated it will load up properly and continue with proper scene loading order.
Does iPad mini 2nd gen has something different from other devices regarding development?
Crash logs says that app crashes immediately after force quit, well duh...
- (void)applicationWillTerminate:(UIApplication *)application
is not really useful, it doesnt detect force app quit.
The idea is that your app should handle termination the same regardless of whether it was initiated by the operating system or by the user. You are encouraged to save the app's state and reload on the next start. And it's probably a good idea to save state when your app is sent to the background because according to the second paragraph below, applicationWillTerminate is not always called when the system kills your app.
According to the documentation
This method lets your app know that it is about to be terminated and purged from memory entirely. You should use this method to perform any final clean-up tasks for your app, such as freeing shared resources, saving user data, and invalidating timers.
Also
For apps that do not support background execution or are linked against iOS 3.x or earlier, this method is always called when the user quits the app. For apps that support background execution, this method is generally not called when the user quits the app because the app simply moves to the background in that case. However, this method may be called in situations where the app is running in the background (not suspended) and the system needs to terminate it for some reason.
I was sitting around bored and thought of this idea. Is it possible to change the WM_DESTROY code so that it will do something else instead of closing the application. But, I don't think this will work, but does that keep it from closing when you try to close the application from the task manager in windows. Also, is there a way to remove my application from the task manager so they wouldn't be able to do that in the first place? So, is this possible or do you have a better way? I have googled this and have tried this, but I want to ask the experienced here to answer this question.
BTW, I am not making a virus.
Windows Task Manager will use TerminateProcess to "close" a process - which is a good thing if your program has accidentally or on purpose got a broken VM_DESTROY handler.
There are supposedly ways to mess about with the process list that hides a process. But I don't actually know how that is done othat than very fundamentally (the process list is a linked list, and you can "unlink" a process from the list, and it "disappears"). Obviously doing so would be the type of thing that virus, trojan's, spyware, etc does, and I don't see any reason why you would want to do that in a legitimate application.
Edit: And hiding the application just means it doesn't appear in the list of processes in task manager. If you KNOW that the task exists (and you could for example "guess" based on system activity or some such), it can still be killed using it's process ID by some application that has enough privileges to terminate the process.
you shoud read win32 api demo. when mainwindow receives WM_DESTROY message, call postquitmessage([exitcode]) to end message loop。
I'm looking for a way to write an application. I use Visual C++ 6.0.
I need to prevent the user from closing this process via task manager.
You can't do it.
Raymond Chen on why this is a bad idea.
You can make an unkillable process, but it won't be able to accomplish anything useful while it's unkillable. For example, one way to make a process unkillable is to have it make synchronous I/O requests to a driver that can never complete (for example, by deliberately writing a buggy driver). The kernel will not allow a process to terminate until the I/O requests finish.
So it's not quite true that you "can't do it" as some people are saying. But you wouldn't want to anyway.
That all depends on who shouldn't be able to kill that process. You usually have one interactively logged-on user. Running the process in that context will alow the user to kill it. It is her process so she can kill it, no surprise here.
If your user has limited privileges you can always start the process as another user. A user can't kill a process belonging to another user (except for the administrator), no surprise here as well.
You can also try to get your process running with Local System privileges where, I think not even an administrator could kill it (even though he could gain permission to do so, iirc).
In general, though, it's a terribly bad idea. Your process does not own the machine, the user does. The only unkillable process on a computer I know is the operating system and rightly so. You have to make sure that you can't hog resources (which can't be released because you're unkillable) and other malicious side-effects. Usually stuff like this isn't the domain of normal applications and they should stay away from that for a reason.
It's a Win32 FAQ for decades. See Google Groups and Und. boards for well-known methods.(hooking cs and others...)
Noobs who answer "You can't do it" know nothing to Win32 programming : you can do everything with Win32 api...
What I've learned from malware:
Create a process that spawns a dozen of itself
Each time you detect that one is missing (it was killed) spawn a dozen more.
Each one should be a unique process name so that a batch process could not easily kill all of them by name
Sequentially close and restart some of the processes to keep the pids changing which would also prevent a batch kill
Depends on the users permission. If you run the program as administrator a normal user will not have enough permissions to kill your process. If an administrator tries to kill the process he will in most cases succeed. If you really want someone not to kill you process you should take a look at windows system services and driver development. In any case, please be aware that if a user cannot kill a process he is stuck with it, even though it behaves abnormally duo to bugs! You will find a huge wealth of these kind of programs/examples on the legal! site rootkit.com. Please respect the user.
I just stumbled upon this post while trying to find a solution to my own (unintentional) unkillable process problem. Maybe my problem will be your solution.
Use jboss Web Native to install a service that will run a batch file (modify service.bat so that it invokes your own batch file)
In your own batch file, invoke a java process that performs whatever task you'd like to persist
Start the service. If you view the process in process explorer, the resulting tree will look like:
jbosssvc.exe -> cmd.exe -> java.exe
use taskkill from an administrative command prompt to kill cmd.exe. Jbosssvc.exe will terminate, and java.exe will be be an orphaned running process that (as far as I can tell) can't be killed. So far, I've tried with Taskmanager, process explorer (running as admin), and taskkill to no avail.
Disclaimer: There are very few instances where doing this is a good idea, as everyone else has said.
There's not a 100% foolproof method, but it should be possible to protect a process this way. Unfortunately, it would require more knowlegde of the Windows security system API than I have right now, but the principle is simple: Let the application run under a different (administrator) account and set the security properties of the process object to the maximum. (Denying all other users the right to close the process, thus only the special administrator account can close it.)
Set up a secondary service and make it run as a process guardian. It should have a lifeline to the protected application and when this lifeline gets cut (the application closes) then it should restart the process again. (This lifeline would be any kind of inter-process communications.)
There are still ways to kill such an unkillable process, though. But that does require knowledge that most users don't really know about, so about 85% of all users won't have a clue to stop your process.
Do keep in mind that there might be legal consequences to creating an application like this. For example, Sony created a rootkit application that installed itself automatically when people inserted a Sony music CD or game CD in their computer. This was part of their DRM solution. Unfortunately, it was quite hard to kill this application and was installed without any warnings to the users. Worse, it had a few weaknesses that would provide hackers with additional ways to get access to those systems and thus to get quite a few of them infected. Sony had to compensate quite a lot of people for damages and had to pay a large fine. (And then I won't even mention the consequences it had on their reputation.)
I would consider such an application to be legal only when you install it on your own computer. If you're planning to sell this application to others, you must tell those buyers how to kill the process, if need be. I know Symantec is doing something similar with their software, which is exactly why I don't use their software anymore. It's my computer, so I should be able to kill any process I like.
The oldest idea in the world, two processes that respawn each other?