Feature #10211
Updated by ko1 (Koichi Sasada) over 9 years ago
Here's pseudocode by ko1:
~~~
# http://www.atdot.net/sp/view/327kbn
def trap2(sig)
previous_proc = Signal.current_trap(sig)
Signal.trap(sig){
previous_proc.call if previous_proc
yield
}
end
trap2(:INT){...}
~~~
## Motivation
I'm developing a gem that allows using multiple callbacks for a trap: [[https://github.com/kyrylo/multitrap]]
It's pretty simple (and slightly broken). The problem is that if you earlier had defined traps and then
required my library, it would discard your previously defined callbacks.
The library overrides `Signal.trap` and stores callbacks in a hash. However, it stores only new callbacks.
I cannot access previously defined callbacks for signals. They are stored in `GET_VM()->trap_list`, which
isn't exposed neither to Ruby nor to the C extension API. I know when you define a `trap`, it returns a proc.
However, nobody typicaly stores it, so there's no way to access it. So if my gem loads after this assignment,
I'm unable to capture that proc, hence I always overwrite previous "traps". This library might be useful if you
want to define a trap that conflicts with some other gem you depend on, which defines its own trap for the
same signal.
So I need some way to access the callbacks.