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|
# frozen_string_literal: true
require_relative "../helper"
require "concurrent"
module Arel
module Visitors
class DummyVisitor < Visitor
def initialize
super
@barrier = Concurrent::CyclicBarrier.new(2)
end
def visit_Arel_Visitors_DummySuperNode(node)
42
end
# This is terrible, but it's the only way to reliably reproduce
# the possible race where two threads attempt to correct the
# dispatch hash at the same time.
def send(*args)
super
rescue
# Both threads try (and fail) to dispatch to the subclass's name
@barrier.wait
raise
ensure
# Then one thread successfully completes (updating the dispatch
# table in the process) before the other finishes raising its
# exception.
Thread.current[:delay].wait if Thread.current[:delay]
end
end
class DummySuperNode
end
class DummySubNode < DummySuperNode
end
class DispatchContaminationTest < Arel::Spec
before do
@connection = Table.engine.connection
@table = Table.new(:users)
end
it "dispatches properly after failing upwards" do
node = Nodes::Union.new(Nodes::True.new, Nodes::False.new)
assert_equal "( TRUE UNION FALSE )", node.to_sql
node.first # from Nodes::Node's Enumerable mixin
assert_equal "( TRUE UNION FALSE )", node.to_sql
end
it "is threadsafe when implementing superclass fallback" do
visitor = DummyVisitor.new
main_thread_finished = Concurrent::Event.new
racing_thread = Thread.new do
Thread.current[:delay] = main_thread_finished
visitor.accept DummySubNode.new
end
assert_equal 42, visitor.accept(DummySubNode.new)
main_thread_finished.set
assert_equal 42, racing_thread.value
end
end
end
end
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