any issues with long running python apps?
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From: geremy condra on 9 Jul 2010 16:42 On Fri, Jul 9, 2010 at 3:13 PM, Les Schaffer <schaffer(a)optonline.net> wrote: > i have been asked to guarantee that a proposed Python application will run > continuously under MS Windows for two months time. And i am looking to know > what i don't know. I normally use Linux for this sort of thing, so YMMV on the following advice. > The app would read instrument data from a serial port, store the data in > file, and display in matplotlib. typical sampling times are about once per > hour. our design would be to read the serial port once a second (long story, > but it worked for ten days straight so far) and just store and display the > values once an hour. so basically we'd have a long running for-loop. maybe > running in a separate thread. I'd keep the two timers, the process that actually checks and logs the data, and any postprocessing code completely separate. I'd also use something like the logging module to double up on where your data is stored- one on the local machine, another physically separated in case you lose a hard drive. It will also give you more information about where a failure might have occurred if/when it does. I'd also handle output/display on a separate machine. > i have thought through the issues on our end: we have to properly handle > the serial port and make sure our GUI doesn't hang easily. we'd have to be > sure we don't have any memory leaks in numpy or matplotlib and we're not > storing data in memory stupidly. i've never looked into Windows serial port > driver reliability over the long term. But we think if the serial port > hangs, we can detect that and react accordingly. I would launch this as a subprocess and log so that even if you miss a measurement you still get what you need further on in the process. Just make sure that you can detect it at the time and that you also log an error when it occurs. This also minimizes the amount of memory your application directly handles and the susceptibility of your code to non-fatal problems with the serial port. > but none of this has anything to do with Python itself. i am sure python > servers have been running reliably for long periods of time, but i've never > had to deal with a two-month guarantee before. is there something else i am > missing here that i should be concerned about on the pure-Python side of > things? something under the hood of the python interpreter that could be > problematic when run for a long time? Just ask all the what-ifs and you'll probably be ok. Geremy Condra
From: Martin P. Hellwig on 9 Jul 2010 17:03 On 07/09/10 20:13, Les Schaffer wrote: > i have been asked to guarantee that a proposed Python application will > run continuously under MS Windows for two months time. And i am looking > to know what i don't know. Get a good lawyer and put into the contract, the last thing you want is a windows update that restarts the host and you are responsible because you guaranteed that it would run continuously. On the technical side; as Christian Heimes already pointed out, split the programs. Specifically I would have 1 service for data gathering, two separate watchdog services (that checks whether the other watchdog is still running and the 'core' service). The GUI should be an user side app and the services could be too, however consider running the services under the appropriate system account as in the past I have seen some strange things happening with services under user account, especially if there are password policies. I don't see from the interpreter point of view no reason why it couldn't work, it is much more likely your host system will mess things up (even if it wouldn't be windows). <cut rest> -- mph
From: John Nagle on 9 Jul 2010 17:19 On 7/9/2010 12:13 PM, Les Schaffer wrote: > i have been asked to guarantee that a proposed Python application will > run continuously under MS Windows for two months time. And i am looking > to know what i don't know. What if Master Control in Redmond decides to reboot your machine to install an update? They've been known to do that even when you thought you had remote update turned off. If you have to run Windows in a data acquistion application, you should be running Windows Embedded. See http://www.microsoft.com/windowsembedded This is a version of Windows 7 which comes with a tool for building customized boot images. Basically, you take out everything except what your application needs. Do you get Embedded Systems Journal? You should. John Nagle
From: Emile van Sebille on 9 Jul 2010 19:30 On 7/9/2010 12:13 PM Les Schaffer said... > i have been asked to guarantee that a proposed Python application will > run continuously under MS Windows for two months time. Keep users off the machine, turn off automated updates, and point dns to 127.0.0.1. Oh, put it on a UPS. I've got a handful or two of these automated systems in place and rarely have trouble. Add a watchdog scheduled task process to restart the job and check disk space or memory usage and push out a heartbeat. I found Chris Liechti's serial module years ago and have used it successfully since. The only times that come to mind when I've problems on the python side were related to memory usage and the system started thrashing. Adding memory fixed it. HTH, Emile > And i am looking > to know what i don't know. > > The app would read instrument data from a serial port, store the data in > file, and display in matplotlib. typical sampling times are about once > per hour. our design would be to read the serial port once a second > (long story, but it worked for ten days straight so far) and just store > and display the values once an hour. so basically we'd have a long > running for-loop. maybe running in a separate thread. > > i have thought through the issues on our end: we have to properly handle > the serial port and make sure our GUI doesn't hang easily. we'd have to > be sure we don't have any memory leaks in numpy or matplotlib and we're > not storing data in memory stupidly. i've never looked into Windows > serial port driver reliability over the long term. But we think if the > serial port hangs, we can detect that and react accordingly. > > but none of this has anything to do with Python itself. i am sure python > servers have been running reliably for long periods of time, but i've > never had to deal with a two-month guarantee before. is there something > else i am missing here that i should be concerned about on the > pure-Python side of things? something under the hood of the python > interpreter that could be problematic when run for a long time? > > or need we only concern ourselves with the nuts behind the wheel:that > is, we the developers? > > thanks > > Les
From: Roy Smith on 9 Jul 2010 19:32
In article <4c3774df$0$31278$607ed4bc(a)cv.net>, Les Schaffer <schaffer(a)optonline.net> wrote: > i have been asked to guarantee that a proposed Python application will > run continuously under MS Windows for two months time. And i am looking > to know what i don't know. Heh. The OS won't stay up that long. |