sidevm: Add sidevm:time::maybe_rest()

[kvinwang]

Guest code can call this API regularly to avoid being stifled.

[h4x3rotab]

The API looks like a blackbox to me. Do you think it's better to make an API that allows the caller to decide the percentage of the remaining gas like this: yield_under_threashold(0.3)? We can make an API with the default value 30% on the guest side.

[kvinwang]

The API looks like a blackbox to me. Do you think it's better to make an API that allows the caller to decide the percentage of the remaining gas like this: yield_under_threashold(0.3)? We can make an API with the default value 30% on the guest side.

I think it's a bit confusing to the caller on how to set the threshold. The take_a_rest_if_needed is already implemented on the guest side. Advanced users can easily implement their own.

BTW, I didn't choose the name yield_ because it sounds like it would require an external resume() to resume the VM.

[h4x3rotab]

OK. Then how about maybe_rest()? It's less verbose than take_a_rest_if_needed.

[kvinwang]

Then how about maybe_rest()? It's less verbose than take_a_rest_if_needed

Sounds OK to me. iOS guys would prefer the verbose one.😄