[New-bugs-announce] [issue6901] Runaway programs often become unresponsive to CTRL-C

Bernie H. Innocenti report at bugs.python.org
Sun Sep 13 20:10:50 CEST 2009

New submission from Bernie H. Innocenti <bernie at codewiz.org>:

On startup, the Python interpreter changes the default behavior
of SIGINT, which results in  many Python programs to ignore the
keyboard interrupt exactly in the situations when users are
most likely to use it (i.e.: when the program becomes unresponsive).

Minimal testcase:
 $ echo "void foo() { for(;;) {} }" >foo.c
 $ gcc -shared -o foo.so foo.c
 $ python -c 'import ctypes;ctypes.CDLL("./foo.so").foo()'

This scenario mimics a Python program calling some blocking library
function.  It can also happen with IO-bound functions if they loop
on read() and don't abort on short reads.

One might be tempted to say "this behavior of the Python intepreter
is by design" and suggest users to use CTRL-\ instead of CTRL-C.
However, this non-standard behavior is very annoying for users who
expect ^C to work on UNIX systems.  In fact, no other compiled or
interpreted language I know of behaves this way, and Python should
not be the only exception.

While I see the usefulness of KeyboardInterrupt from the programmer
point of view, only a minority of programs actually need to trap
SIGINT and do something with it.  Other language runtimes require
the programmer to manually trap SIGINT when needed.  The Python
interpreter could maintain backwards compatibility by enabling
automatic SIGINT trapping when entering a  "try" block that would
intercept KeyboardInterrupt.

components: Interpreter Core
messages: 92576
nosy: bernie
severity: normal
status: open
title: Runaway programs often become unresponsive to CTRL-C
versions: Python 2.6, Python 3.0

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