I set a timeout using Python signal to put a limit on how long an integral can take (since as far as I know python itself does not have a timeout constraint support to use on a call to a function, so one must program this in)
If integrate takes more than some number of seconds, an exception is raised. This way my script does not hang on an integral.
I found it works with fricas, but not with maxima. i.e. when I set the algorithm to maxima, and pick an integral that takes too long and set the timeout to short time (10 seconds), the exception never fires. It means the signal was lost or ignored.
When I do the same thing, set the algorithm to fricas, and pick an integral that also takes long time for fricas to do, the timeout works.
Same exact code. Only difference is the algorithm used.
May be the way I am setting timer is not the best, and there are more robust ways to do this. But I do not understand now why it works with fricas and not with maxima. Here is an example. This is file called test_hanged.sag
#!/usr/bin/env sage
import sys, os, signal, time
from sage.all import *
class TimeoutError(Exception):
pass
def handler(signum,frame):
print("handler fired")
raise TimeoutError()
signal.signal(signal.SIGALRM, handler)
signal.alarm(10) #10 seconds time out
try:
#this call will hang. Timer is either lost or ignored. Only with maxima
integrate(sqrt(x^2 + 1)*arctan(x)^2,x, algorithm="maxima")
#never reach here
signal.alarm(0)
print "Finished "
except Exception as e:
#this never gets called. It is supposed to be called after 10 seconds
print "exception=", type(e).__name__
print "finished...."
The I do $ ./test_hang.sage it just hangs. Now the following with fricas, works. Same code. Just changed the call to integrate
#!/usr/bin/env sage
import sys, os, signal, time
from sage.all import *
class TimeoutError(Exception):
pass
def handler(signum,frame):
print("handler fired")
raise TimeoutError()
signal.signal(signal.SIGALRM, handler)
signal.alarm(10) #10 seconds time out
try:
#this call will hang or take too long if there is no timeout
integrate((x+(1+x)^(1/2))^(1/2)/(x^2+1)/(1+x)^(1/2),x,algorithm="fricas")
#never reach here, due to time out
signal.alarm(0)
print "Finished "
except Exception as e:
#this is now called. So timer worked.
print "exception=", type(e).__name__
print "finished...."
And now
./test_hang.sage
handler fired
exception= TimeoutError
finished....
Any idea why the above works with fricas and not with maxima? I need now to try to find better way to do timeouts, as the above does not work for all.
