Functionality in subprocess.Popen.terminate()
In my GSoC project, I have implemented asnychronous I/O in subprocess.Popen. Since the read/write operations are asynchronous, the program may have already exited by the time one calls the asyncread function I have implemented. While it returns the data just fine, I have come across an issue with the TerminateProcess function in Windows: if the program has already exited, when subprocess.Popen.Terminate calls the Windows built-in "TerminateProcess" function, an "access denied" error will occur. Should I just make it so that this exception is simply ignored or perform some kind of check to see if the process exists beforehand? If the latter, I have been unable to find a way to do so, to my liking at least. The solutions I saw would require code that seems a bit excessive to me. Eric
Eric Pruitt wrote:
In my GSoC project, I have implemented asnychronous I/O in subprocess.Popen. Since the read/write operations are asynchronous, the program may have already exited by the time one calls the asyncread function I have implemented. While it returns the data just fine, I have come across an issue with the TerminateProcess function in Windows: if the program has already exited, when subprocess.Popen.Terminate calls the Windows built-in "TerminateProcess" function, an "access denied" error will occur. Should I just make it so that this exception is simply ignored or perform some kind of check to see if the process exists beforehand? If the latter, I have been unable to find a way to do so, to my liking at least. The solutions I saw would require code that seems a bit excessive to me.
I'm pretty sure we already ignore some spurious error messages in cases like calling flush() in file.close(). I would suggest checking what the io module does in such cases and see what kind of precedent it sets. Cheers, Nick. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia ---------------------------------------------------------------
On Tue, Aug 4, 2009 at 04:27, Nick Coghlan<ncoghlan@gmail.com> wrote:
Eric Pruitt wrote:
In my GSoC project, I have implemented asnychronous I/O in subprocess.Popen. Since the read/write operations are asynchronous, the program may have already exited by the time one calls the asyncread function I have implemented. While it returns the data just fine, I have come across an issue with the TerminateProcess function in Windows: if the program has already exited, when subprocess.Popen.Terminate calls the Windows built-in "TerminateProcess" function, an "access denied" error will occur. Should I just make it so that this exception is simply ignored or perform some kind of check to see if the process exists beforehand? If the latter, I have been unable to find a way to do so, to my liking at least. The solutions I saw would require code that seems a bit excessive to me.
I'm pretty sure we already ignore some spurious error messages in cases like calling flush() in file.close(). I would suggest checking what the io module does in such cases and see what kind of precedent it sets.
Cheers, Nick.
-- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia ---------------------------------------------------------------
Sounds good enough to me but I was wondering if it might be a good idea to add a function like "pidinuse" to subprocess as a whole that would determine if a process ID was being used and return a simple boolean value. I came across a number of people searching for a way to determine if a PID was running (Google "python check if pid exists") so it seems like the implemented functionality would be of use to the community as a whole, not just my wrapper class. Eric
Eric Pruitt wrote:
On Tue, Aug 4, 2009 at 04:27, Nick Coghlan<ncoghlan@gmail.com> wrote:
In my GSoC project, I have implemented asnychronous I/O in subprocess.Popen. Since the read/write operations are asynchronous, the program may have already exited by the time one calls the asyncread function I have implemented. While it returns the data just fine, I have come across an issue with the TerminateProcess function in Windows: if the program has already exited, when subprocess.Popen.Terminate calls the Windows built-in "TerminateProcess" function, an "access denied" error will occur. Should I just make it so that this exception is simply ignored or perform some kind of check to see if the process exists beforehand? If the latter, I have been unable to find a way to do so, to my liking at least. The solutions I saw would require code that seems a bit excessive to me. I'm pretty sure we already ignore some spurious error messages in cases
Eric Pruitt wrote: like calling flush() in file.close(). I would suggest checking what the io module does in such cases and see what kind of precedent it sets.
Cheers, Nick.
-- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia ---------------------------------------------------------------
Sounds good enough to me but I was wondering if it might be a good idea to add a function like "pidinuse" to subprocess as a whole that would determine if a process ID was being used and return a simple boolean value. I came across a number of people searching for a way to determine if a PID was running (Google "python check if pid exists") so it seems like the implemented functionality would be of use to the community as a whole, not just my wrapper class.
Eric
I'm not sure of the actual details but it seems from your description that even if you check first a race condition will still exist. Specifically the subprocess could terminate after the check and before the TerminateProcess call. So it seems better just to call TerminateProcess and then correctly handle any possible error. Janzert
Janzert wrote:
Eric Pruitt wrote:
Sounds good enough to me but I was wondering if it might be a good idea to add a function like "pidinuse" to subprocess as a whole that would determine if a process ID was being used and return a simple boolean value. I came across a number of people searching for a way to determine if a PID was running (Google "python check if pid exists") so it seems like the implemented functionality would be of use to the community as a whole, not just my wrapper class.
Eric
I'm not sure of the actual details but it seems from your description that even if you check first a race condition will still exist. Specifically the subprocess could terminate after the check and before the TerminateProcess call. So it seems better just to call TerminateProcess and then correctly handle any possible error.
Janzert is correct here - this is a case where ruling out the error completely is impossible, so you're going to have to handle it regardless. A cross platform way of checking if a particular subprocess is still running might be an interesting feature in its own right, but I don't think it will prevent this exception. Cheers, Nick. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia ---------------------------------------------------------------
participants (3)
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Eric Pruitt -
Janzert -
Nick Coghlan