Kill misbehaving children

[bmegli]

It can happen that misbehaving module (on EV3) is stuck on blocking IO (e.g. laser waititing for synchronization without running motor properly) and will not know that it's stdin was closed by ev3control.

This way request from ev3control to disable module will wait indefinitely.

Give some timeout for child to close and if it is naughty kill it with a signal.

A child will get SIGINT in IO call and finish gracefully (at least this is what modules already do on SIGINT in most cases).

So:

• kindly ask child to quit with closing it's stdin (gets EOF)
• if it's naughty kill it with a gentle signal so that it still has a chance to gracefully cleanup after self

Optionally if it's still misbehaving after that kill it mercilessly

[bmegli]

Implementation Plan

• close the child stdin (control pipe end)
• MODULE_DISABLE_TRIES times sleep MODULE_DISABLE_MS and try nonblocking waitpid
• if child is still alive send SIGINT to child and MODULE_DISABLE_TRIES sleep MODULE_DISABLE_MS and try nonblocking waitpid
• finally if the child still resists send SIGKILL and MODULE_DISABLE_TRIES sleep MODULE_DISABLE_MS and try nonblocking waitpid
• if child is still alive inform on stderr

Other info

Initally: MODULE_DISABLE_TRIES=3 MODULE_DISABLE_MS=50