After completing a load, give other threads a chance too

While we know no user code is running, we should do as much loading as
we can. That way, all the threads will then be able to resume running
user code together.

Otherwise, only the last arriving thread would get to do its load, and
would then return to userspace, leaving the others still blocked.

1 files changed, 17 insertions, 0 deletions

diff --git a/activesupport/test/share_lock_test.rb b/activesupport/test/share_lock_test.rb
index 3475ee94cd..12953d99a6 100644
--- a/activesupport/test/share_lock_test.rb
+++ b/activesupport/test/share_lock_test.rb
@@ -270,6 +270,23 @@ class ShareLockTest < ActiveSupport::TestCase
     end
   end
 
+  def test_compatible_exclusives_cooperate_to_both_proceed
+    ready = Concurrent::CyclicBarrier.new(2)
+    done = Concurrent::CyclicBarrier.new(2)
+
+    threads = 2.times.map do
+      Thread.new do
+        @lock.sharing do
+          ready.wait
+          @lock.exclusive(purpose: :x, compatible: [:x], after_compatible: [:x]) {}
+          done.wait
+        end
+      end
+    end
+
+    assert_threads_not_stuck threads
+  end
+
   def test_in_shared_section_incompatible_non_upgrading_threads_cannot_preempt_upgrading_threads
     scratch_pad       = []
     scratch_pad_mutex = Mutex.new