Can I pause a computation rather than aborting it?
Sometimes I don't want to discard work by raising an exception. It would be nice if I could just pause execution ad hoc.
You can find the PID of the working process by typing os.getpid() in the worksheet. So to do what you want now, try the following:
os.getpid() and note the PID.factor(2^997-1)) going in the first worksheet. import signal; os.kill(that pid above, signal.SIGSTOP). The first worksheet will appear to be running, but will not use any CPU resources, as you can confirm with top on the server. os.kill(that pid above, signal.SIGCONT). You will see in top that the Python process associated with the first worksheet is back and burning resources. The point of the above exercise is that it illustrates that a pause feature could fully work. To really do this right, one would need to add something to the Sage Notebook itself, e.g., modify the sagenb spkg. This would involve some GUI design choices, etc.
Does the worksheet process do the spawning then (is it the parent)? If so, the PID could be displayed by default for worksheets (since a person might not call os.getpid() first, by forgetting). Or does twisted spawn the processes? Neither? In any case it would be a cool project.
A related project might be accounting for spawned time. I've noticed that "%time" sometimes puts almost everything in Wall time, which strictly speaking is correct, but not as interesting as a 3-way breakdown. A more difficult project perhaps.
Twisted spawns the worksheet process. It can determine the PID of that process.
There currently isn't any way to pause a computation in the notebook. The only way I can think of the implement such a thing would be to send a SIGTSTP signal to the worker process, but I do not know how the pexpect interface to that process would behave.
How would I find the proper parent process to send a cascade of SIGTSTPs?
Mike -- this is a very good idea. I think it would be likely to work. ccanonc -- as you probably know, on the command line you can just hit "control-Z" to pause, and "fg" to start again.
When I say "likely to work", I mean "with a bunch of work, eventually it could be made to work".
Mike: I wish I could mark both answers as favorite, but I don't think I can. I think it would be a good askbot enhancement: to have a max threshold. I'll comment on that Q&A thread.
I thought that William's was better than mine :-)
Asked: 14 years ago
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Last updated: Aug 24 '10
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Harder: It would be nice if I could inspect the paused state too.