Is there a way to cancel and reschedule tkinter after() events when the system time is updated, or preemptively update the after() scheduler?
Description
I have a custom GUI created in tkinter using Python3.7 on Raspbian (fork of Debian-Linux for Raspberri Pi). I created a screen to adjust the system time.
If the date & time are set to the future, everything is OK, but if it's set to the past, anything using the tkinter after() method to schedule events never happens. I believe after() works by polling system time, and the scheduled times are now far in the future.
I verified this by setting the time for a minute into the past. Initially, any elements using the after() function stopped updating, but the GUI was still responsive to click events. A minute later, those elements continued to update.
Related
This Question back in 2010 is about the same problem, but has no solutions.
Side Note - the user running the GUI doesn't have privileges to set the time, so it is actually starting a service (which it has the privilege to do), and writing a time string to a FIFO pipe. The service running as root reads the pipe and updates the time. I have verified the time is correctly set with this method.
Update
I never came up with a good way for this to work. So I have a message box to say that application would need to restart after the time change so the user at least knew what was about to happen. If they were OK with that, the application terminated and relaunched itself.
Related
I am creating an application for linux and want to put the device screen in sleep mode after a particular time like 5 minutes, 10 minutes etc if no response or event occur by the user side.
Piggybacking on the other answer a bit here.
You could install an eventFilter at a top-level in your application to monitor any input events as they occur (whether that be a mouse click or move event, keyboard event, etc.). At the same scope as that eventFilter, you could then use some QTimer with the interval set to your sleep timeout duration, which you restart every time an input occurs. That QTimer's timeout signal could be hooked up to a slot where you put the system to sleep via a QProcess call out to sh for example.
I do not think that there is a possibility for qt to do that, because a sleep mode is handled by the desktop environment like GNOME, Xfce, and so on. Qt itself isn't able to do this, but maybe you could use a function which just sends a command to the os, which has the opportunity to set the system to sleep. Maybe this could help you:
https://linuxer.eu/put-linux-into-sleep-from-command-line/
I have made this AutoHotKey script after reading the manual, searching and troubleshooting for endless hours in the last few weeks:
#Persistent
#SingleInstance force
if A_Args[1] > 0
{
Menu, Tray, Icon, C:\blablabla\new notifications.png
}
else
{
Menu, Tray, Icon, C:\blablabla\no new notifications.png
}
This, I have compiled into test.exe. Then I call it like this from a terminal: test.exe 1, test.exe 0, test.exe 2, test.exe 3, etc.
If I do it slowly/manually, it works: it only ever keeps one instance of the script, showing visually as a nice little icon in the Notification area (as intended), never launching multiple instances.
However, when I started actually using it for real, by calling the same terminal command from my scripts, it often opens two or more instances, which are kept open and just make the Notification area longer and longer, ignoring the rule that it only can run as one instance ever.
I was able to "solve" it by introducing a short "sleep" in my script after each such command call, so that the same script never calls it too quickly in succession. However, today, I realized that multiple different scripts of mine often call it at the same time, or nearly at the same time. This means that my "clever" solution of sleeping falls short.
I then thought that I can use the database to keep track of when the last time a script called this, and don't do it if it's too soon, but if I did that, the whole point would be lost since I can no longer trust the icon to accurately tell me whether or not there are new notifications in my system. I'd constantly be wondering if there had been such a "race condition" and manually go and check anyway, defeating the point of this visual indication which is supposed to let me always know "at a glance" whether or not there are new notifications in my system.
Maybe I could have a loop in my scripts and repeatedly re-try if it detects that a notification has been sent too recently, but that means my scripts will potentially stall for a long time as they all send notifications (especially in the morning, when I wake up and kickstart my system). It just seems like the wrong solution.
Is there really no way to properly handle this in the script itself? As is obvious from my description, the #Persistent and #SingleInstance force rules aren't respected.
(I've had similar problems in the past with programs being unable to "handle" running commands too quickly, and I never know what to do about it except to introduce sleep. But even then, it often glitches out. For example, Notepad++ requires me to first open a document and then open it again with a specified line number, sleeping in between, or else it doesn't go to the specified line.)
I have a wxApp implementation in which the wxFrame embeds a CEF browser.I have bindings from CEF framework to perform some Javascript bindings. The application shows up the initial screen and loads everything good. However, after a certain delay (not consistent), the app frame becomes non-responsive and does not handle any of the events. I have put up a wxTimer to figure out the amount of time it takes and it varies between 28 seconds to 60 seconds. This is where the timer events are also not called. Now when I press on the x or maximize icon on the window, all the pending events are sent and the application becomes active again.
Here are the options I tried:
Called wxTheApp->ProcessPendingEvents(); on the timer (runs every 1 second)
Tried and looked into onIdle method. This is also getting paused after a while
My guess is that the application main thread is paused for some reason and is not able to revert back unless any of the UI actions are triggering it.
I develop a SCADA in python3 with the help of PyQt. I expect my program to continuously indicate various parameters received through RS-485 interface, however, within several minutes from the start (it is always a different time), the GUI stops to update itself. At the same time, the GUI stays responsive and if I were to click on one of the animated QAbstractButtons it has, the GUI starts to work as intended again for a short period of time. The problem occurs on both Linux and Windows.
The program has several worker threads: one for RS-485 exchange, one for reading/writing various data to disk, one for decoding received package and refreshing data in memory, one for request queue management, etc. They all work in loops of while (True): time.sleep(...) - do the job. The GUI is implemented in the main thread.
The data is indicated with QLabels. The QLabel.setText is added to painterEvent() of QWidgets containing the QLabels.
When the GUI stops updating, the other threads are up and running: the exchange is functioning, the request queue is forming, etc. Despite not being updated, the GUI stays responsive and reacts to QAbstractButton clicks.
I tried adding gui.update() or app.processEvents() into one of the worker threads, tried force updating through QTimer in the main thread. The result is the same: it works for a short while and then stops.
I tried increasing the time.sleep of the refresh thread and force updating the main widget over longer intervals of time (0.5 to 5 seconds) and it seems to help the situation a lot, this way it can run for several minutes, but it still does not solve the problem.
I would love to show the code, but the whole thing is way too bulky to post here and if I could narrow it down to a at least a hundred lines, I would have already solved the issue by now. So if any of you could at least share some general considerations on what to look for, I would be very happy.
update:
This seems to work, I'll leave it running for a few hours tomorrow to confirm:
update_timer = QTimer()
update_timer.setSingleShot(False)
update_timer.timeout.connect(self.gui.repaint)
update_timer.setInterval(500)
update_timer.start()
I assume that self.gui.update() did not work because dataChanged() was probably not emitted and control passed instead of doing repaint(). As far as I understand, the solution above is not the right way to update widgets.
So, the question actually boils down to the following:
What is the right way to update the main QWidget and how do I let the program know it needs to be redrawn, probably using dataChanged() signal?
The answer is simple. Never do anything related to PyQt from outside the main thread. Even if it seems the only logical way to do something.
After I 'fixed' the issue with the gui not being updated, I stumbled into a more serious problem: the program crashed every now and then. As it turns out, the GUI not being updated was only the top of the iceberg. The uptime was usually 2 to 7 minutes, I received a few glibc errors ("corrupted double-linked list" and "double free or corrution"). As it turns out, the source of the problem was inside refresh thread that has several hundreds of lines updating gui:
self.gui.screen_name.device_name.setCrash()
where setCrash() changes widget color and palette, or even more direct things like
self.gui.screen_name.label_name.setText(str(value))
I tracked down everything even loosely related to gui from the main file (the place where all the threading took place) and restyled it. Now it only has one worker thread - the RS-485, the rest are wrapped into separate QTimers.
This is what it was:
class Main():
def __init__():
self.plots_thread = Thread(target = self.plots_refresh)
self.plots_thread.start()
def plots_refresh():
while True:
time.sleep(0.5)
#do stuff
And this is what it is now:
class Main():
def __init__():
self.plots_refresh_timer = QTimer()
self.plots_refresh_timer.setSingleShot(False)
self.plots_refresh_timer.timeout.connect(self.plots_refresh)
self.plots_refresh_timer.setInterval(499) #prime number
self.plots_refresh_timer.start()
def plots_refresh():
#do stuff
This time the program has been running for over an hour and never crashed. After coming to conclusion that this was THE fix, I refactored the really messy test file and resumed testing - again, no troubles for half an hour.
I have a large data acquisition and control program written in Python3.4.2 using GUI mostly developed on Glade 3.18.3, Gtk3.0 GObject running Debian 8 with XFCE.
There are timers that keep doing things, and these work fine. After startup, the program runs for some 3 - 7 days, then suddenly, all of the windows go blank and stay blank. Other applications are not affected. Memory and CPU usage is modest.
There are no indications of problems prior to the windows going blank. The windows show their title bars and respond normally to minimize, restore, move to another Workspace, etc. It looks like they are not getting repainted - no widgets are visible at all. The code is way too large to post here, and I am not able to isolate a specific problem area for lack of obvious symptoms other than the blank screens. There are no error messages or warnings.
The timers continue to run, acquire data and control things. This happens whether the program is run from the command line or under PyDev in Eclipse.
Things I have tried:
In the main timer loop, I put code to look for a file, and then exec the command in it, printing the results, so I have been able to mess with the program in real time:
Replace the usual Gtk.main() with a while loop whose variable, if not made false, will re-execute the Gtk.main(). Executing Gtk.main.quit() stops Gtk.main and starts it again. Windows still blank. Did this repeatedly to no avail.
Experimented with garbage collection with GC. Collecting garbage makes no different. Windows still blank.
Put in code to print percent of time consumed by the timer loops. Fairly steady around 18 - 20% of available CPU time, so nothing is hogging the CPU preventing re-paint.
I have a button that clears a label. I read the label, then executed a builder.get_object(...).activate command to the button. I re-read the label and it was now properly blank. So events and widgets appear to be working normally, at least to some extent.
Finally, if I click on the close X on the title bar, XFCE asks me if I want to wait or close now. So it seems as though there may be a disconnection or problem with signals and the OS, even though XXX.activate() works.
Web searching is in vain. Does anybody have ideas of what might be happening, useful diagnostics, or other suggestions? Many thanks!
April 27, 2017 Update:
I have taken two substantial steps to mostly work around problems. First, partly in response to a couple of Gtk crashes over the last few months, instead of ending the main program with:
Gtk.main()
I end with:
while wannalive:
try:
Gtk.main()
except:
pass
wannalive is True until user does a quit, so recovery is instant.
Second, I grouped all of the code for each window setup and initial population of static items into two functions. I also made another function for closing a window. These functions propagate to children, grandchildren windows. A function in the top window first, closes, then re-creates all windows, with one call. In operation, there are overlaps in what windows exist, but that is not a problem.
Above, I describe that I can inject code with an external program. The external program has a button that injects a call to that third function. In about five seconds or less, the result of a single button click is to replace all blank windows with functional windows. For my purposes in a controlled environment with a trained operator, this is acceptable.
Next, let me address the relationship between the timer loops and GUI events processing. I do use GObject.timeout_add(ms, somefunction). Experiment shows that a button that calls time.sleep(5) stalls the timer. Experiment shows that injecting time.sleep(5) in the timer loop stalls the GUI. This is consistent with my belief (correct me if I am wrong) that Python runs on a single thread. Therefore, bad code caught in an infinite loop should stall both the GUI and the timer loop. (The program has one timeout_add call.)