pass options to delegators when they accept it

[dnesteryuk]

This change reduces hash allocations.

Here is a simplified example what was happening.

def do_not_accept_keywords(**)
end

100.times { do_not_accept_keywords(hash: true) }

After measuring via memory profiler, we got this:

Total allocated: 69600 bytes (300 objects)

allocated memory by location
-----------------------------------
     69600  profile/sample.rb:15

It points to a line where the method gets called. So, every call created a separate hash. It was happening for Grape::Entity::Delegator::PlainObject.

If options get extracted, the picture is better.

def do_not_accept_keywords(**)
end

opts = { hash: true }

100.times { do_not_accept_keywords(opts) }

Allocation:

Total allocated: 46632 bytes (201 objects)

allocated memory by location
-----------------------------------
     46400  profile/sample.rb:15
       232  profile/sample.rb:13

However, there is no object allocation if nothing is passed to the method.

Total allocated: 0 bytes (0 objects)

Btw, if a method "swallows" arguments, but nothing is passed, there is still allocation.

def do_not_accept_keywords(**)
end

100.times { do_not_accept_keywords }

Result:

Total allocated: 23200 bytes (100 objects)

allocated memory by location
-----------------------------------
     23200  profile/sample.rb:15

The splat operator brings its cost.

So, now Grape Entity checks whether the delegetor accepts options before passing them.

I measured this change against our production:

Before:

Total allocated: 1512362 bytes (12328 objects)

allocated memory by location
-----------------------------------
    605520  /usr/local/bundle/gems/grape-entity-0.8.0/lib/grape_entity/entity.rb:537 

After:

Total allocated: 908402 bytes (9733 objects)

allocated memory by location
-----------------------------------
     18000  /app/grape-entity/lib/grape_entity/entity.rb:553

0.57 MB of RAM were saved while serving the identical request.

[coveralls]

Coverage increased (+0.03%) to 95.792% when pulling c7c18c9 on dnesteryuk:attr_delegation into ab3238d on ruby-grape:master.

[coveralls]

Coverage increased (+0.03%) to 95.792% when pulling c7c18c9 on dnesteryuk:attr_delegation into ab3238d on ruby-grape:master.

[coveralls]

Coverage increased (+0.1%) to 95.898% when pulling 2023ea8 on dnesteryuk:attr_delegation into ab3238d on ruby-grape:master.

[grape-bot]

	1 Warning
⚠️	There’re library changes, but not tests. That’s OK as long as you’re refactoring existing code.

Generated by 🚫 danger

[grape-bot]

	1 Warning
⚠️	There’re library changes, but not tests. That’s OK as long as you’re refactoring existing code.

Generated by 🚫 danger

[LeFnord]

thanks @dnesteryuk … especially for the explanation

but … can it have implications on upgrade?

[dnesteryuk]

@LeFnord I don't see how it might impact existing code in projects which use grape entity 🤔