From 9f2df7856d0515f097d517395f944e6faf414d6d Mon Sep 17 00:00:00 2001
From: thedarkone <thedarkone2@gmail.com>
Date: Sun, 7 Feb 2016 00:57:37 +0100
Subject: AS::Conc::ShareLock#yield_shares tests.

---
 activesupport/test/share_lock_test.rb | 107 ++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)

diff --git a/activesupport/test/share_lock_test.rb b/activesupport/test/share_lock_test.rb
index 68fa5bb69e..5fceebf023 100644
--- a/activesupport/test/share_lock_test.rb
+++ b/activesupport/test/share_lock_test.rb
@@ -313,6 +313,113 @@ class ShareLockTest < ActiveSupport::TestCase
     assert_threads_not_stuck threads
   end
 
+  def test_manual_incompatible_yield
+    ready = Concurrent::CyclicBarrier.new(2)
+    done = Concurrent::CyclicBarrier.new(2)
+
+    threads = [
+      Thread.new do
+        @lock.sharing do
+          ready.wait
+          @lock.exclusive(purpose: :x) {}
+          done.wait
+        end
+      end,
+
+      Thread.new do
+        @lock.sharing do
+          ready.wait
+          @lock.yield_shares(compatible: [:y]) do
+            done.wait
+          end
+        end
+      end,
+    ]
+
+    assert_threads_stuck threads
+  ensure
+    threads.each(&:kill) if threads
+  end
+
+  def test_manual_recursive_yield
+    ready = Concurrent::CyclicBarrier.new(2)
+    done = Concurrent::CyclicBarrier.new(2)
+    do_compatible_nesting = Concurrent::CountDownLatch.new
+
+    threads = [
+      Thread.new do
+        @lock.sharing do
+          ready.wait
+          @lock.exclusive(purpose: :x) {}
+          done.wait
+        end
+      end,
+
+      Thread.new do
+        @lock.sharing do
+          ready.wait
+          @lock.yield_shares(compatible: [:y]) do
+            do_compatible_nesting.wait
+            @lock.sharing do
+              @lock.yield_shares(compatible: [:x, :y]) do
+                done.wait
+              end
+            end
+          end
+        end
+      end
+    ]
+
+    assert_threads_stuck threads
+    do_compatible_nesting.count_down
+    assert_threads_not_stuck threads
+  end
+
+  def test_manual_recursive_yield_restores_previous_compatible
+    ready = Concurrent::CyclicBarrier.new(2)
+    do_nesting = Concurrent::CountDownLatch.new
+    after_nesting = Concurrent::CountDownLatch.new
+
+    incompatible_thread = Thread.new do
+      ready.wait
+      @lock.exclusive(purpose: :z) {}
+    end
+
+    recursive_yield_shares_thread = Thread.new do
+      @lock.sharing do
+        ready.wait
+        @lock.yield_shares(compatible: [:y]) do
+          do_nesting.wait
+          @lock.sharing do
+            @lock.yield_shares(compatible: [:x, :y]) {}
+          end
+          after_nesting.wait
+        end
+      end
+    end
+
+    assert_threads_stuck incompatible_thread
+    do_nesting.count_down
+    assert_threads_stuck incompatible_thread
+
+    compatible_thread = Thread.new do
+      @lock.exclusive(purpose: :y) {}
+    end
+    assert_threads_not_stuck compatible_thread
+
+    post_nesting_incompatible_thread = Thread.new do
+      @lock.exclusive(purpose: :x) {}
+    end
+    assert_threads_stuck post_nesting_incompatible_thread
+
+    after_nesting.count_down
+    assert_threads_not_stuck recursive_yield_shares_thread
+    # post_nesting_incompatible_thread can now proceed
+    assert_threads_not_stuck post_nesting_incompatible_thread
+    # assert_threads_not_stuck can now proceed
+    assert_threads_not_stuck incompatible_thread
+  end
+
   def test_in_shared_section_incompatible_non_upgrading_threads_cannot_preempt_upgrading_threads
     scratch_pad       = []
     scratch_pad_mutex = Mutex.new
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