I have a working application that needs to clear and setup very large buffers from time to time. Sometimes the operation takes longer than 5 seconds to complete and then Desktop Window Manager times out and declares the application to be hung.
Is there any technique to cause DWM to allow more time before this happens?
Delphi Seattle, Windows 10, 64-bit application
The right solution is to put the long running task in a thread so that it does not block your UI thread. You should do that.
If you cannot bring yourself to take that task one, and it can be quite tricky, you can always disable ghosting by calling DisableProcessWindowsGhosting. But you really ought not to do that. You really ought to put the work in a thread.
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Summary
When putting the monitor in sleep mode in Windows 10, Windows seems to execute some tasks that don't get executed with the screen on.
This is interfering with our software, and we need to get rid of it.
Ful story
For a hardware device with a touch screen, I need to be able to turn off the touch screen when it's not in use, for durability reasons. Windows has a message that you can send to turn it off, SC_MONITORPOWER. More specifically:
SendMessage(hwnd, WM_SYSCOMMAND, SC_MONITORPOWER, 2);
This works fine, but when the screen is off, Windows is apparently sometimes performing some tasks that it doesn't do when the screen is on. We are careful to never write anything to the screen in this situation (that causes huge problems when the screen is off, in fact just having a blinking cursor in a DOS box is using up half a core when the screen is off).
Our software requires a callback to be executed every 0.25 ms. We have turned nearly every task, service and several other things in Windows off, and with the screen on, I can run our software for days without ever missing a callback. But with the screen off I get hiccups. The callback already runs at the highest possible priority.
So there is apparently something that we missed when we turned all services and tasks off. There appear to be 2 causes of hiccups:
One happens once every 10-30 hours or so (not sure of the exact time, it seems to vary). But it always happens 5 times, with EXACTLY 5 minutes (at most a few milliseconds off) in between (so in total it happens 5 times in a 25 minute period).
Beside this, we get a single hiccup typically every 4-10 hours, but the time between occurrences doesn't seem to be very constant so there could also be multiple causes.
I'm a bit at a loss here, and running analysis software can easily interfere with our own software, making it harder to detect when these hiccups really occur and when they are caused by running the analysis software.
Interestingly, I have seen this 5-times-every-5-minutes thing also on a completely different system (different hardware, different OS version), when recording audio in Adobe Audition. Audition misses pieces of audio every 5 minutes in this case, and I think it also only happens when the monitor is in sleep mode and you're not logged in remotely.
We have already tried to turn the touch screen off using direct monitor commands like Nircmd does, and it doesn't support those. My guess is that the SC_MONITORPOWER message is triggering more things in Windows, and if we can turn them off, that would fix our problem. Any ideas?
System
Intel i5-8700 with 6 cores, Windows LTSB, no extra software installed except our own.
Never mind, problem solved. It was not an extra task that was being started, it was one of the existing Windows processes that for some reason only causes issues when the display is off. Since killing them is not an option (Windows will just restart them), I've suspended the following processes, and the culprit is one of these (I don't know which one yet):
sihost.exe
igfxEM.exe (I very much suspect this one)
RuntimeBroker.exe
dllhost.exe
taskhostw.exe
explorer.exe
I have to continue testing a bit longer to be absolutely certain, but so far with these tasks all suspended I've not seen a missed callback in the last 38 hours. I don't know yet if there are any drawbacks to suspending all these things, so I'll try to find the cause(s) and suspend only that/those.
UWP (or "Metro") apps in Windows 8/10 are frequently suspended when they are not in the foreground. Apps in this state continue to exist but no longer consume CPU time. This change seems to have been introduced to improve performance on low-power/storage devices like tablets and phones.
Please can I ask, what is the most elegant and simple method to detect an app in this state?
I can see 2 possible solutions at the moment:
Call NtQuerySystemInformation() and the enumerate each process and each thread. A process is "suspended" if all threads are in the suspended state. This approach will require a lot of code and critically NtQuerySystemInformation() is only semi-documented and could be removed in a future OS. NtQueryInformationProcess() may also offer a solution with the same problem.
Call GetProcessTimes() and record the counters for each process. Wait some time (minutes) and check these again. If the process counters haven't changed then assume the process is suspended. This is a hack and I may get shot down for even thinking of it.
Jim
The second one (GetProcessTimes() … wait … and check these again.
If the process counters haven’t changed then assume the process is suspended)
is less reliable.
If a process is waiting for input (e.g., keyboard, mouse, or network)
and not getting any, it will use very little CPU time
and will appear to be suspended by this approach.
happens to me occasionally:
I start my program in visual studio and due to some bug my program goes into 100% cpu usage and basically freezes windows completely.
Only by utter patience requesting the task manager (takes forever to come up and paint itself) I can kill my process.
Do others encounter this too sometimes? Is there a clever trick to get this process down (other than pulling the plug and possible ruining files on the HD)? It now takes 5-10 minutes to kill it properly if the task manager is not accidentally present and I have to request this first
R
p.s. weird that a 'multitasking os' can still allow processes to eat up so much time that nothing else can be done anymore. My program doesn't even bump up it's thread priorities or anything
Check out Process Lasso
"Process Lasso is a unique new technology that will, amongst other things, improve your PC's responsiveness and stability. Windows, by design, allows programs to monopolize your CPU without restraint -- leading to freezes and hangs. Process Lasso's ProBalance (Process Balance) technology intelligently adjusts the priority of running programs so that badly behaved or overly active processes won't interfere with your ability to use the computer!"
http://www.bitsum.com/prolasso.php
I am not affiliated with Bitsum, just a user of their product, and it helps me solve this type of problems.
For what it's worth, I've never see this on either XP 64 or Vista 64, developing C++ apps in Visual Studio. Perhaps an OS upgrade is in order?
Edit: I use Process Explorer as a replacement Task Manager - it wouldn't surprise me if it did a better job of appearing in good time even when there's a rogue process running. And you can use it to boost its own priority.
I usually hit ctrl-alt-delete start the task manager sort by cpu find the offending process and right click and end the process..
task manager usually has enough priority to do this although it may be slow.
I think a shotgun to the head is the only way to be sure.
I generally don't see anything like this happen strictly as a function of an app that's eating 100% CPU. As part of stability / performance testing, I've gotten apps to cause Windows to get very slow, but this is usually done by writing heavily threaded apps (thus causing the O/S scheduler to thrash), or by writing apps that consume all available system memory or resources (much more impactful to the GUI apps than simply one thread that consumes its full share of processor time during its slices).
You say you get this behavior under Visual Studio? VS has a "Pause" button...
I have heard a myth that a job will finish faster if it is kept as the active window, and not in the background or minimized.
Is there any truth to this? Does the CPU put precedence to tasks where this happens?
Thanks,
On Windows the foreground application gets a priority boost. This is to help it maintain responsiveness to the user and makes sure that when it's ready to run after waiting for some I/O event, it'll get to run next, ahead of most other applications that might be waiting to run.
There is also a potential for a longer quantum for foreground applications.
I don't know how much faster an application would complete if it's run in the foreground instead of the background - there are so many factors that would go into this (particularly I/O). The intent is to make the application more responsive.
This is all configurable to some extent (maybe only on server SKUs):
http://support.microsoft.com/kb/259025
It depends on your setup. On a default Windows desktop operating system, this is true. On a Windows server operating system (like Windows 2003) this is not true.
You can change the setting by going into System Properties and clicking on the Performance tab. The exact layout differs depending on Windows version, but you should see (or be able to see by clicking an Advanced sub tab or finding "Scheduler") either a radio/combo choice between "Workstation" and "Server" configuration, or a choice between prioritizing Programs or Background Services. In both cases these are the same thing (just different language - the Server/Workstation language is from Windows 2000, while Programs/Services was created for the more consumer oriented XP) - they determine if the scheduler gives extra importance to the thread of the top most window, or if all threads are treated equally (based on the thread prioritity property).
Windows allows you to give the "foreground" task a priority advantage, so it may be no myth. You can also set it the other way, to give "service" tasks the priority advantage instead, so it depends on the install.
Note that this only affects the priority... if there are no other tasks running, it won't run noticeably different in either case. It's only when there is another application that needs CPU time that you might notice the difference.
That's partially true on Windows. Windows would assign a GUI application that has its window on-top slightly higher priority. So if there're other tasks with normal or lower priority the program could really run a bit faster at the expense of other programs running a bit slower.
There's catch however. When you start compilation in Visual Studio IDE the IDE will spawn a separate process for the compilation and only redirect its output to its own window. Since the compilation process now has no own windows it will not gain acceleration.
When Mac OS X goes to sleep, due to closing a laptop or selecting "Sleep" from the Apple menu, how does it suspend an executing process?
I suppose non-windowed processes are simply suspended at an arbitrary point of execution. Is that also true for Cocoa apps, or does the OS wait until control returns to the run loop dispatcher, and goes to sleep in a "known" location? Does any modern OS do that, or is it usually safe enough to simply suspend an app no matter what it is doing?
I'm curious, because allowing sleep to occur at any moment means, from the app's perspective, the system clock could suddenly leap forward by a significant amount. That's a possibility I don't usually consider while coding.
Your app is interrupted exactly where it is that moment if the CPU is actually currently executing code of your app. Your app constantly gets execution time by the task scheduler, that decides which app gets CPU time, on which core, and for how long. Once the system really goes to sleep, the scheduler simply gives no time to your app any longer, thus it will stop execution wherever it is at that moment, which can happen pretty much everywhere. However, the kernel must be in a clean state. That means if you just made a call into the kernel (many libC functions do) and this call is not at some safe-point (e.g. sleeping, waiting for a condition to become true, etc.) or possibly holding critical kernel locks (e.g. funnels), the kernel may suspend sleep till this call returns back to user space or execution reaches such a safe-point before it finally cancels your app from the task scheduler.
You can open a kernel port and register for sleep/wake-up events. In that case, your app will receive an event, when the system wants to go to sleep. You have several possibilities. One is to reply to it, that the system may progress. Another one is to suspend sleep; however, Apple says certain events can be suspended at most 30 seconds, after that, the system will just continue, whether your app likes it or not. And finally, you can cancel it; though not all events can be canceled. If the system already decided it will go to sleep, you can only suspend this by at most 30 seconds or allow it at once, you cannot cancel it. However, you can also listen to an event, where the system asks apps, if it is okay to go to sleep now and there you can reply "no", causing a sleep to be canceled.
The difference between "Is it okay to sleep" and "I'm planing on going to sleep" is: The first one is sent if the power saving settings are applied, that is, if the user has not moved the mouse or typed anything for the time configured there. In that case the system will just ask, if sleep is okay. An app like Apple's DVD Player will say "no", because most likely the user watches a DVD and thus doesn't interact with the computer, still no reason to go to sleep. OTOH, if the user closes his Mac Book, apps are not asked, the system will go to sleep for sure and just informs apps, that have now up to 30 seconds to react to it.
Wake-up events can also be quite interesting to catch. E.g. if your system wakes up, open files might be inaccessible (an external drive has been unplugged) or network sockets won't work any longer (network has changed). So you may re-init certain app parts before using them and running into errors that are more or less expected.
Apple's page regarding catching these events.
It depends on your app.
If you are interacting with external systems (think networking or doing something over usb/firewire,etc) then it might be affected. An application running on OSX gets to run for a limited time ( max 10ms ) , after which it is interrupted by the kernel which schedules a new process from the process queue to run on the CPU. This is transparent for the application , which "thinks" that it runs all the time on the CPU. Thus , a transition to sleep is no different - apart from the time jumping ahead.
If you need to be aware that there was a transition to sleep mode please refer to this tech note which details how to receive notifications about the state change : Registering and unregistering for sleep and wake notifications
I believe it will just suspend all apps wherever they happen to be.
Remember, this happens all the time anyway. Applications are constantly suspended and resumed due to context switching. So, really, the clock could jump between any 2 instructions in your app, though usually not in a noticable/significant way.
If the OS waited for the app to return to some main loop you could run into situations where applications cause the sleep to hang. If they're doing a lot of work and not returning to the run loop dispatcher they would prevent the machine from going to sleep. That wouldn't be very good. :)
And if you set the time it also appears to leap forward to the running programs. Nothing special either.
Check out this Wikipedia article. Cavver is correct in stating that things like network connections may time out, and thus those services may be interrupted.