Block new share attempts if there's an exclusive waiter

1 files changed, 32 insertions, 0 deletions

diff --git a/activesupport/test/share_lock_test.rb b/activesupport/test/share_lock_test.rb
index 465a657308..0a5b074bee 100644
--- a/activesupport/test/share_lock_test.rb
+++ b/activesupport/test/share_lock_test.rb
@@ -114,14 +114,17 @@ class ShareLockTest < ActiveSupport::TestCase
     [true, false].each do |use_upgrading|
       with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
         begin
+          together = Concurrent::CyclicBarrier.new(2)
           conflicting_exclusive_threads = [
             Thread.new do
               @lock.send(use_upgrading ? :sharing : :tap) do
+                together.wait
                 @lock.exclusive(purpose: :red, compatible: [:green, :purple]) {}
               end
             end,
             Thread.new do
               @lock.send(use_upgrading ? :sharing : :tap) do
+                together.wait
                 @lock.exclusive(purpose: :blue, compatible: [:green]) {}
               end
             end
@@ -183,11 +186,14 @@ class ShareLockTest < ActiveSupport::TestCase
     load_params   = [:load,   [:load]]
     unload_params = [:unload, [:unload, :load]]
 
+    all_sharing = Concurrent::CyclicBarrier.new(4)
+
     [load_params, load_params, unload_params, unload_params].permutation do |thread_params|
       with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
         threads = thread_params.map do |purpose, compatible|
           Thread.new do
             @lock.sharing do
+              all_sharing.wait
               @lock.exclusive(purpose: purpose, compatible: compatible) do
                 scratch_pad_mutex.synchronize { scratch_pad << purpose }
               end
@@ -209,6 +215,32 @@ class ShareLockTest < ActiveSupport::TestCase
     end
   end
 
+  def test_new_share_attempts_block_on_waiting_exclusive
+    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
+      release_exclusive = Concurrent::CountDownLatch.new
+
+      waiting_exclusive = Thread.new do
+        @lock.sharing do
+          @lock.exclusive do
+            release_exclusive.wait
+          end
+        end
+      end
+      assert_threads_stuck waiting_exclusive
+
+      late_share_attempt = Thread.new do
+        @lock.sharing {}
+      end
+      assert_threads_stuck late_share_attempt
+
+      sharing_thread_release_latch.count_down
+      assert_threads_stuck late_share_attempt
+
+      release_exclusive.count_down
+      assert_threads_not_stuck late_share_attempt
+    end
+  end
+
   def test_in_shared_section_incompatible_non_upgrading_threads_cannot_preempt_upgrading_threads
     scratch_pad       = []
     scratch_pad_mutex = Mutex.new