Exit forked processes immediately to avoid a SQLite mutex deadlock at exit

lib/puma/plugin/solid_queue.rb

@@ -33,6 +33,11 @@ def start_forked(launcher)
           @solid_queue_pid = fork do
             Thread.new { monitor_puma }
             SolidQueue::Supervisor.start(mode: :fork)
+
+            # Same as Processes::Supervised#create_fork: skip at-exit
+            # finalization, which can deadlock on database handles when a
+            # thread was killed while inside a query
+            exit!(0)
           end
         end
 
@@ -43,6 +48,11 @@ def start_forked(launcher)
           @solid_queue_pid = fork do
             Thread.new { monitor_puma }
             start_solid_queue(mode: :fork)
+
+            # Same as Processes::Supervised#create_fork: skip at-exit
+            # finalization, which can deadlock on database handles when a
+            # thread was killed while inside a query
+            exit!(0)
           end
         end
 

lib/solid_queue/processes/supervised.rb

@@ -29,6 +29,14 @@ def create_fork(&block)
         fork do
           register_signal_handlers
           block.call
+
+          # Exit skipping at-exit hooks and finalizers, like Puma's cluster
+          # workers do: Ruby would finalize every object still alive in the
+          # fork, including SQLite database handles whose mutex can be left
+          # locked when a thread is killed while waiting in SQLite's busy
+          # handler, deadlocking the exit. Everything the process needs to do
+          # on shutdown has already run by now.
+          exit!(0)
         end
       end
 

test/dummy/config/puma_async.rb

@@ -13,10 +13,6 @@
 #
 worker_timeout 3600 if ENV.fetch("RAILS_ENV", "development") == "development"
 
-# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
-#
-port ENV.fetch("PORT") { 3000 }
-
 # Specifies the `environment` that Puma will run in.
 #
 environment ENV.fetch("RAILS_ENV") { "development" }

test/dummy/config/puma_fork.rb

@@ -13,10 +13,6 @@
 #
 worker_timeout 3600 if ENV.fetch("RAILS_ENV", "development") == "development"
 
-# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
-#
-port ENV.fetch("PORT") { 3000 }
-
 # Specifies the `environment` that Puma will run in.
 #
 environment ENV.fetch("RAILS_ENV") { "development" }

test/unit/supervised_test.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class SupervisedTest < ActiveSupport::TestCase
+  class FakeProcess
+    include SolidQueue::Processes::Supervised
+
+    def stop
+    end
+  end
+
+  test "forked processes exit immediately, without running inherited at-exit hooks" do
+    reader, writer = IO.pipe
+
+    pid = FakeProcess.new.send(:create_fork) do
+      at_exit { writer.write("at_exit ran") }
+      writer.write("block ran")
+    end
+
+    writer.close
+    _, status = Process.waitpid2(pid)
+
+    assert_equal 0, status.exitstatus
+    assert_equal "block ran", reader.read
+  ensure
+    reader.close
+  end
+end