From a6c01974b16b0a9c76101dfac529e5ca1ee8007b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A9=20Dupuis?= <joe@dupuis.io>
Date: Sat, 23 Mar 2024 14:09:17 -0700
Subject: [PATCH] Fix a crash when an  Executor wrapped fork exit.

Fix #51298

forking inside an Execution Wrapper crashes when running the completion callbacks.

Rails 7.0 was not Execution wrapping the `runner` command.
Rails 7.2 changed the definition of `active_connection?`, the new definition doesn't contain the bug.

Therefore forking inside a script intended to be run with the `runner` command on 7.1 crashes. (see #51298)
---
 activerecord/lib/active_record/query_cache.rb |  2 +-
 activerecord/test/cases/query_cache_test.rb   | 31 +++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/activerecord/lib/active_record/query_cache.rb b/activerecord/lib/active_record/query_cache.rb
index 08db278880fe1..3765986567fef 100644
--- a/activerecord/lib/active_record/query_cache.rb
+++ b/activerecord/lib/active_record/query_cache.rb
@@ -30,7 +30,7 @@ def self.run
     end
 
     def self.complete(pools)
-      pools.each { |pool| pool.disable_query_cache! }
+      pools.each { |pool| pool.disable_query_cache! unless pool.discarded? }
 
       ActiveRecord::Base.connection_handler.each_connection_pool do |pool|
         pool.release_connection if pool.active_connection? && !pool.connection.transaction_open?
diff --git a/activerecord/test/cases/query_cache_test.rb b/activerecord/test/cases/query_cache_test.rb
index 43a4031405888..91b8842cb05ae 100644
--- a/activerecord/test/cases/query_cache_test.rb
+++ b/activerecord/test/cases/query_cache_test.rb
@@ -650,6 +650,37 @@ def test_clear_query_cache_is_called_on_all_connections
     ActiveRecord::Base.connection_pool.lock_thread = false
   end
 
+  test "query cache callbacks exit gracefully from a fork" do
+    # Regression test for #51298
+    pid = nil
+    status = nil
+
+    # Run forking Rack app
+    middleware { |env|
+      pid = fork
+      _, status = Process.wait2(pid) if pid.present?
+      [200, {}, nil]
+    }.call({})
+
+
+    # Happy path, the fork exit 0 and the main process
+    # asserts on the exit status of the fork
+    if pid.nil?
+      exit 0
+    else
+      assert_equal 0, status.exitstatus
+    end
+  rescue
+    # Unhappy path, the fork exit 1.
+    # The main process should not reach here, but in case
+    # something's wrong we need to re-raise the error.
+    if pid.nil?
+      exit 1
+    else
+      raise
+    end
+  end
+
   private
     def with_temporary_connection_pool(&block)
       pool_config = ActiveRecord::Base.connection.pool.pool_config