From 111874d8b57ed8772981d46091eb02e2e81344de Mon Sep 17 00:00:00 2001
From: Adam Markowitz <adam@looker.com>
Date: Fri, 1 Sep 2017 12:31:47 -0700
Subject: [PATCH 1/3] resolve waiting counter problem

if a thread is in the wait state, but transitions into
a killed state the waiting counter will not be decremented
leaving the pool to believe there is a thread available
and waiting to complete work when that is not the case.
Introduce a begin..ensure block so that any thread exception
raised while in the wait state properly balances the
waiting counter.
---
 lib/puma/thread_pool.rb  |  7 +++++--
 test/test_thread_pool.rb | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/lib/puma/thread_pool.rb b/lib/puma/thread_pool.rb
index c0bbedb1..bb6a73c7 100644
--- a/lib/puma/thread_pool.rb
+++ b/lib/puma/thread_pool.rb
@@ -122,8 +122,11 @@ module Puma
                 @out_of_band_pending = false
               end
               not_full.signal
-              not_empty.wait mutex
-              @waiting -= 1
+              begin
+                not_empty.wait mutex
+              ensure
+                @waiting -= 1
+              end
             end
 
             work = todo.shift
diff --git a/test/test_thread_pool.rb b/test/test_thread_pool.rb
index 697f5c46..ccc07ae0 100644
--- a/test/test_thread_pool.rb
+++ b/test/test_thread_pool.rb
@@ -266,4 +266,24 @@ class TestThreadPool < Minitest::Test
     assert_equal 2, rescued.length
     refute rescued.compact.any?(&:alive?)
   end
+
+  def test_correct_waiting_count_for_killed_threads
+    pool = new_pool(1, 1) { |_| }
+
+    pause
+
+    # simulate our waiting worker thread getting killed for whatever reason
+    pool.instance_eval { @workers[0].kill }
+
+    pause
+
+    pool.reap
+
+    pause
+
+    pool << 0
+
+    pause
+    assert_equal 0, pool.backlog
+  end
 end

From 7f095b4445eabe70e2f4ae806b30ce7e26a20402 Mon Sep 17 00:00:00 2001
From: "John W. Phillips" <johnwphillips@google.com>
Date: Wed, 10 Jun 2020 23:24:34 +0000
Subject: [PATCH 2/3] Resolve waiting counter issue

---
 History.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/History.md b/History.md
index 6f066bbd..72752d6d 100644
--- a/History.md
+++ b/History.md
@@ -1,3 +1,7 @@
+### Master
+* Bugfixes
+  * Resolve issue with threadpool waiting counter decrement when thread is killed
+
 ## 5.0.0
 
 * Features

From 7dfd9fba25c61d37e17be4bb7935fd38aff11793 Mon Sep 17 00:00:00 2001
From: "John W. Phillips" <johnwphillips@google.com>
Date: Wed, 10 Jun 2020 23:25:24 +0000
Subject: [PATCH 3/3] Update syntax of unit test.

---
 test/test_thread_pool.rb | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/test/test_thread_pool.rb b/test/test_thread_pool.rb
index ccc07ae0..0e6f7645 100644
--- a/test/test_thread_pool.rb
+++ b/test/test_thread_pool.rb
@@ -269,21 +269,16 @@ class TestThreadPool < Minitest::Test
 
   def test_correct_waiting_count_for_killed_threads
     pool = new_pool(1, 1) { |_| }
-
-    pause
+    sleep 1
 
     # simulate our waiting worker thread getting killed for whatever reason
     pool.instance_eval { @workers[0].kill }
-
-    pause
-
+    sleep 1
     pool.reap
-
-    pause
+    sleep 1
 
     pool << 0
-
-    pause
+    sleep 1
     assert_equal 0, pool.backlog
   end
 end