diff options
Diffstat (limited to 'activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb')
-rw-r--r-- | activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb b/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb new file mode 100644 index 0000000000..a07a1a050a --- /dev/null +++ b/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb @@ -0,0 +1,72 @@ +# 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 |