Enabling keepalive if a physical action exists

[Soroosh129]

Imagine the following LF program:

target Python;
reactor Foo {
    physical action a;
    reaction(a) {=
        print("A physical event has occurred")
    =}
}
main reactor {
    f = new Foo();
}

This program exits as soon as it starts. The only reason for this is that the (at least C and Python) runtimes think that no events exist in this program and keepalive is set to false. Therefore, they decide to exit the program. However, if a physical action exists, there is no way for the runtime to make such a determination by itself, since a physical action can produce an event at any given moment in perpetuity.

This issue was recently rediscovered by @housengw while trying to implementation the C target sensor simulator in the Python target.

I would suggest that to err on the safe side, we should set keepalive to true when physical actions exist in a program, unless the user has explicitly set it to false. What do you think?

I have created a draft PR that reflects the changes required for this feature in #546.

[edwardalee]

I thought we already had this. In any case, I think we should definitely set keepalive to true if there are physical actions.

[lhstrh]

#546 has been merged into master.