discourse/spec/support/concurrency.rb

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# frozen_string_literal: true
require 'fiber'
module Concurrency
module Logic
class DeadEnd < StandardError; end
module Complete
class Path
def initialize
@path = []
@index = 0
end
def to_s
"#<Logic::Complete::Path path=#{@path}>"
end
def choose(*options)
raise DeadEnd if options.empty?
@path << [options.size, 0] unless @index < @path.size
pair = @path[@index]
raise "non-determinism" unless pair[0] == options.size
@index += 1
options[pair[1]]
end
def choose_with_weights(*options)
choose(options.map(&:first))
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end
def dead_end
raise DeadEnd
end
def guard(condition)
dead_end unless condition
end
def next
@index = 0
until @path.empty?
pair = @path.last
pair[1] += 1
if pair[1] < pair[0]
break
else
@path.pop
end
end
!@path.empty?
end
end
def self.run(&blk)
path = Path.new
possibilities = []
while true
begin
possibilities << blk.call(path)
rescue DeadEnd
end
break unless path.next
end
possibilities
end
end
module Sampling
class Path
def initialize(random)
@random = random
end
def to_s
"#<Logic::Sampling::Path seed=#{@random.seed}>"
end
def choose(*options)
options.sample(random: @random)
end
def choose_with_weights(*options)
position = @random.rand
options.each do |(option, weight)|
if position <= weight
return option
else
position -= weight
end
end
raise "weights don't add up"
end
def dead_end
raise DeadEnd
end
def guard(condition)
dead_end unless condition
end
end
def self.run(seed, runs, &blk)
seed = seed.to_i
possibilities = []
runs.times do |i|
path = Path.new(Random.new(seed + i))
begin
possibilities << blk.call(path)
rescue DeadEnd
end
end
possibilities
end
end
def self.run(seed: nil, runs: nil, &blk)
if runs.present?
Sampling.run(seed, runs, &blk)
else
Complete.run(&blk)
end
end
end
class Scenario
def initialize(&blk)
@blk = blk
end
class Execution
attr_reader :path
def initialize(path)
@path = path
@tasks = []
end
def yield
Fiber.yield
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end
def choose(*options)
@path.choose(*options)
end
def choose_with_weights(*options)
@path.choose_with_weights(*options)
end
def spawn(&blk)
@tasks << Fiber.new(&blk)
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end
def run
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until @tasks.empty?
task = @path.choose(*@tasks)
task.resume
unless task.alive?
@tasks.delete(task)
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end
end
end
end
def run_with_path(path)
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execution = Execution.new(path)
result = @blk.call(execution)
execution.run
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result
end
def run(**opts)
Logic.run(**opts, &method(:run_with_path))
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end
end
class RedisWrapper
def initialize(redis, execution)
@redis = redis
@execution = execution
@in_transaction = false
end
def multi(&blk)
with_possible_failure do
with_in_transaction do
@redis.multi(&blk)
end
end
end
def method_missing(method, *args, &blk)
if @in_transaction
@redis.send(method, *args, &blk)
else
with_possible_failure do
@redis.send(method, *args, &blk)
end
end
end
private
def with_in_transaction
previous_value, @in_transaction = @in_transaction, true
begin
yield
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ensure
@in_transaction = previous_value
end
end
def with_possible_failure
outcome =
@execution.choose_with_weights(
[:succeed, 0.96],
[:fail_before, 0.02],
[:fail_after, 0.02]
)
@execution.yield
if outcome == :fail_before
raise Redis::ConnectionError
end
result = yield
@execution.yield
if outcome == :fail_after
raise Redis::ConnectionError
end
result
end
end
end