```ruby
require 'action_pack'
require 'action_dispatch'
require 'benchmark/ips'
route_set = ActionDispatch::Routing::RouteSet.new
routes = ActionDispatch::Routing::Mapper.new route_set
ObjectSpace::AllocationTracer.setup(%i{path line type})
result = ObjectSpace::AllocationTracer.trace do
500.times do
routes.resources :foo
end
end
sorted = ObjectSpace::AllocationTracer.allocated_count_table.sort_by(&:last)
sorted.each do |k,v|
next if v == 0
p k => v
end
__END__
Before:
{:T_SYMBOL=>11}
{:T_REGEXP=>17}
{:T_STRUCT=>6500}
{:T_MATCH=>12004}
{:T_OBJECT=>99009}
{:T_DATA=>100088}
{:T_HASH=>122015}
{:T_STRING=>159637}
{:T_IMEMO=>363134}
{:T_ARRAY=>433056}
After:
{:T_SYMBOL=>11}
{:T_REGEXP=>17}
{:T_STRUCT=>6500}
{:T_MATCH=>12004}
{:T_OBJECT=>91009}
{:T_DATA=>100088}
{:T_HASH=>114013}
{:T_STRING=>159637}
{:T_ARRAY=>321056}
{:T_IMEMO=>351133}
```
Eagerly calculate and cache the name of Symbol objects in the path AST.
This drops about 26 string allocations per resource:
```ruby
require 'action_pack'
require 'action_dispatch'
require 'benchmark/ips'
route_set = ActionDispatch::Routing::RouteSet.new
routes = ActionDispatch::Routing::Mapper.new route_set
ObjectSpace::AllocationTracer.setup(%i{path line type})
result = ObjectSpace::AllocationTracer.trace do
500.times do
routes.resources :foo
end
end
sorted = ObjectSpace::AllocationTracer.allocated_count_table.sort_by(&:last)
sorted.each do |k,v|
next if v == 0
p k => v
end
__END__
Before:
{:T_SYMBOL=>11}
{:T_REGEXP=>17}
{:T_STRUCT=>6500}
{:T_MATCH=>12004}
{:T_OBJECT=>99009}
{:T_DATA=>116084}
{:T_HASH=>122015}
{:T_STRING=>172647}
{:T_IMEMO=>371132}
{:T_ARRAY=>433056}
After:
{:T_SYMBOL=>11}
{:T_REGEXP=>17}
{:T_STRUCT=>6500}
{:T_MATCH=>12004}
{:T_OBJECT=>99009}
{:T_DATA=>100088}
{:T_HASH=>122015}
{:T_STRING=>159637}
{:T_IMEMO=>363134}
{:T_ARRAY=>433056}
```
This commit introduces a functional Path AST visitor and implements
`each` on the AST in terms of the functional visitor. The functional
visitor doesn't maintain state, so we only need to allocate one of them.
Given this benchmark route file:
```ruby
require 'action_pack'
require 'action_dispatch'
route_set = ActionDispatch::Routing::RouteSet.new
routes = ActionDispatch::Routing::Mapper.new route_set
ObjectSpace::AllocationTracer.setup(%i{path line type})
result = ObjectSpace::AllocationTracer.trace do
500.times{|i|
routes.resource :omglol
}
end
result.find_all { |k,v| k.first =~ /git\/rails/ }.sort_by { |k,v|
v.first
}.each { |k,v|
p k => v
}
```
node.rb line 17 was in our top 3 allocation spot:
```
{["/Users/aaron/git/rails/actionpack/lib/action_dispatch/journey/nodes/node.rb", 17, :T_OBJECT]=>[31526, 0, 28329, 0, 2, 1123160]}
{["/Users/aaron/git/rails/actionpack/lib/action_dispatch/routing/mapper.rb", 2080, :T_IMEMO]=>[34002, 0, 30563, 0, 2, 1211480]}
{["/Users/aaron/git/rails/actionpack/lib/action_dispatch/routing/mapper.rb", 2071, :T_IMEMO]=>[121934, 1, 109608, 0, 7, 4344400]}
```
This commit eliminates allocations at that place.
I wrote a utility that helps find areas where you could optimize your program using a frozen string instead of a string literal, it's called [let_it_go](https://github.com/schneems/let_it_go). After going through the output and adding `.freeze` I was able to eliminate the creation of 1,114 string objects on EVERY request to [codetriage](codetriage.com). How does this impact execution?
To look at memory:
```ruby
require 'get_process_mem'
mem = GetProcessMem.new
GC.start
GC.disable
1_114.times { " " }
before = mem.mb
after = mem.mb
GC.enable
puts "Diff: #{after - before} mb"
```
Creating 1,114 string objects results in `Diff: 0.03125 mb` of RAM allocated on every request. Or 1mb every 32 requests.
To look at raw speed:
```ruby
require 'benchmark/ips'
number_of_objects_reduced = 1_114
Benchmark.ips do |x|
x.report("freeze") { number_of_objects_reduced.times { " ".freeze } }
x.report("no-freeze") { number_of_objects_reduced.times { " " } }
end
```
We get the results
```
Calculating -------------------------------------
freeze 1.428k i/100ms
no-freeze 609.000 i/100ms
-------------------------------------------------
freeze 14.363k (± 8.5%) i/s - 71.400k
no-freeze 6.084k (± 8.1%) i/s - 30.450k
```
Now we can do some maths:
```ruby
ips = 6_226k # iterations / 1 second
call_time_before = 1.0 / ips # seconds per iteration
ips = 15_254 # iterations / 1 second
call_time_after = 1.0 / ips # seconds per iteration
diff = call_time_before - call_time_after
number_of_objects_reduced * diff * 100
# => 0.4530373333993266 miliseconds saved per request
```
So we're shaving off 1 second of execution time for every 220 requests.
Is this going to be an insane speed boost to any Rails app: nope. Should we merge it: yep.
p.s. If you know of a method call that doesn't modify a string input such as [String#gsub](b0e2da69f0/lib/let_it_go/core_ext/string.rb (L37)) please [give me a pull request to the appropriate file](b0e2da69f0/lib/let_it_go/core_ext/string.rb (L37)), or open an issue in LetItGo so we can track and freeze more strings.
Keep those strings Frozen
Move the Journey code underneath the ActionDispatch namespace so
that we don't pollute the global namespace with names that may
be used for models.
Fixesrails/journey#49.
