Removed `data` ivar from JSON::Validator so that multiple `validate` call become faster

[ganmacs]

In my environment, I call JSON::Validator.validate many times with huge JSON Schema definitions and it takes a lot of time to return value. After some investigations, I found that JSON::Validator#initialize_schema in JSON::Validator#initialize takes most of the time.

This patch removes @data from instance variables of JSON::Validator so that it can avoid a lot of duplicated object creation. it's really useful and efficient when you want to apply the same schema but different data multiple time.

schema = ....
validator = JSON::Validator.new(schema)

validator.validate(data1)
validator.validate(data2)
validator.validate(data3)

flamegraph

code: https://gist.github.com/ganmacs/29f6217bbd3658d7f1f0010d0cadedd7 (json_schema_test.rb)

$ bundle exec ruby json_schema_test.rb
$ stackprof --flamegraph stackprof.dump > flamegraph
$ stackprof --flamegraph-viewer=flamegraph

Before

After

benchmark

code: https://gist.github.com/ganmacs/29f6217bbd3658d7f1f0010d0cadedd7 (benchmark.rb)

       user     system      total        real
before 100  0.137017   0.020746   0.157763 (  0.158190)
before 1000  1.349775   0.209938   1.559713 (  1.572352)
before 5000  6.520370   0.991955   7.512325 (  7.585911)
after 100  0.040351   0.010675   0.051026 (  0.051197)
after 1000  0.373515   0.096487   0.470002 (  0.471269)
after 5000  2.010080   0.548916   2.558996 (  2.582410)

[codecov[bot]]

Codecov Report

Merging #465 (d96b036) into master (081dfc3) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #465   +/-   ##
=======================================
  Coverage   89.83%   89.84%           
=======================================
  Files          74       74           
  Lines        1555     1556    +1     
=======================================
+ Hits         1397     1398    +1     
  Misses        158      158           

Impacted Files	Coverage Δ
lib/json-schema/validator.rb	85.06% <100.00%> (+0.04%)	:arrow_up:

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[bastelfreak]

@ganmacs thanks for the PR. Could you rebase please to pull in our latest CI changes?

[ganmacs]

Thank you guys for your review. Rebased.