Introduce support for fiber-per-request.

This enables the correct scope of `Fiber.storage` per request.

- Unify `clean_thread_locals` and `fiber_per_request` configuration options.

lib/puma/configuration.rb

@@ -128,7 +128,7 @@ class Configuration
     DEFAULTS = {
       auto_trim_time: 30,
       binds: ['tcp://0.0.0.0:9292'.freeze],
-      clean_thread_locals: false,
+      fiber_per_request: ENV["PUMA_FIBER_PER_REQUEST"] == "true",
       debug: false,
       early_hints: nil,
       environment: 'development'.freeze,

lib/puma/dsl.rb

@@ -333,12 +333,15 @@ def idle_timeout(seconds)
       @options[:idle_timeout] = Integer(seconds)
     end
 
-    # Work around leaky apps that leave garbage in Thread locals
-    # across requests.
-    def clean_thread_locals(which=true)
-      @options[:clean_thread_locals] = which
+    # Use a clean fiber per request which ensures a clean slate for thread
+    # locals, fiber locals and fiber storage. Also provides a cleaner
+    # backtrace with less Puma internal stack frames.
+    def fiber_per_request(which=true)
+      @options[:fiber_per_request] = which
     end
 
+    alias clean_thread_locals fiber_per_request
+
     # When shutting down, drain the accept socket of pending connections and
     # process them. This loops over the accept socket until there are no more
     # read events and then stops looking and waits for the requests to finish.

lib/puma/server.rb

@@ -32,6 +32,14 @@ module Puma
   #
   # Each `Puma::Server` will have one reactor and one thread pool.
   class Server
+    module FiberPerRequest
+      def handle_request(client, requests)
+        Fiber.new do
+          super
+        end.resume
+      end
+    end
+
     include Puma::Const
     include Request
 
@@ -98,6 +106,10 @@ def initialize(app, events = nil, options = {})
       @io_selector_backend       = @options[:io_selector_backend]
       @http_content_length_limit = @options[:http_content_length_limit]
 
+      if @options[:fiber_per_request]
+        singleton_class.prepend(FiberPerRequest)
+      end
+
       # make this a hash, since we prefer `key?` over `include?`
       @supported_http_methods =
         if @options[:supported_http_methods] == :any
@@ -442,7 +454,6 @@ def process_client(client)
       # Advertise this server into the thread
       Thread.current.puma_server = self
 
-      clean_thread_locals = options[:clean_thread_locals]
       close_socket = true
 
       requests = 0
@@ -471,8 +482,6 @@ def process_client(client)
             close_socket = false
             break
           when true
-            ThreadPool.clean_thread_locals if clean_thread_locals
-
             requests += 1
 
             # As an optimization, try to read the next request from the

lib/puma/thread_pool.rb

@@ -50,7 +50,6 @@ def initialize(name, options = {}, &block)
       @shutdown_grace_time = Float(options[:pool_shutdown_grace_time] || SHUTDOWN_GRACE_TIME)
       @block = block
       @out_of_band = options[:out_of_band]
-      @clean_thread_locals = options[:clean_thread_locals]
       @before_thread_start = options[:before_thread_start]
       @before_thread_exit = options[:before_thread_exit]
       @reaping_time = options[:reaping_time]
@@ -79,12 +78,6 @@ def initialize(name, options = {}, &block)
 
     attr_reader :spawned, :trim_requested, :waiting
 
-    def self.clean_thread_locals
-      Thread.current.keys.each do |key| # rubocop: disable Style/HashEachMethods
-        Thread.current[key] = nil unless key == :__recursive_key__
-      end
-    end
-
     # How many objects have yet to be processed by the pool?
     #
     def backlog
@@ -147,10 +140,6 @@ def spawn_thread
             work = todo.shift
           end
 
-          if @clean_thread_locals
-            ThreadPool.clean_thread_locals
-          end
-
           begin
             @out_of_band_pending = true if block.call(work)
           rescue Exception => e

test/test_fiber_local_application.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2023, by Samuel Williams.
+
+require_relative "helper"
+
+require "puma/server"
+
+class FiberLocalApplication
+  def call(env)
+    # Just in case you didn't know, this is fiber local...
+    count = (Thread.current[:request_count] ||= 0)
+    Thread.current[:request_count] += 1
+    [200, {"Content-Type" => "text/plain"}, [count.to_s]]
+  end
+end
+
+class FiberLocalApplicationTest < Minitest::Test
+  parallelize_me!
+
+  def setup
+    @tester = FiberLocalApplication.new
+    @server = Puma::Server.new @tester, nil, {log_writer: Puma::LogWriter.strings, fiber_per_request: true}
+    @port = (@server.add_tcp_listener "127.0.0.1", 0).addr[1]
+    @tcp = "http://127.0.0.1:#{@port}"
+    @server.run
+  end
+
+  def teardown
+    @server.stop(true)
+  end
+
+  def test_empty_locals
+    response = hit(["#{@tcp}/test"] * 3)
+    assert_equal ["0", "0", "0"], response
+  end
+end

test/test_fiber_storage_application.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2023, by Samuel Williams.
+
+require_relative "helper"
+
+require "puma/server"
+
+class FiberStorageApplication
+  def call(env)
+    count = (Fiber[:request_count] ||= 0)
+    Fiber[:request_count] += 1
+    [200, {"Content-Type" => "text/plain"}, [count.to_s]]
+  end
+end
+
+class FiberStorageApplicationTest < Minitest::Test
+  parallelize_me!
+
+  def setup
+    skip "Fiber Storage is not supported on this Ruby" unless Fiber.respond_to?(:[])
+
+    @tester = FiberStorageApplication.new
+    @server = Puma::Server.new @tester, nil, {log_writer: Puma::LogWriter.strings, fiber_per_request: true}
+    @port = (@server.add_tcp_listener "127.0.0.1", 0).addr[1]
+    @tcp = "http://127.0.0.1:#{@port}"
+    @server.run
+  end
+
+  def teardown
+    @server.stop(true)
+  end
+
+  def test_empty_storage
+    response = hit(["#{@tcp}/test"] * 3)
+    assert_equal ["0", "0", "0"], response
+  end
+end

test/test_thread_pool.rb

@@ -227,24 +227,6 @@ def test_autotrim
     assert_equal 1, pool.spawned
   end
 
-  def test_cleanliness
-    values = []
-    n = 100
-
-    pool = mutex_pool(1,1) {
-      values.push Thread.current[:foo]
-      Thread.current[:foo] = :hai
-    }
-
-    pool.instance_variable_set :@clean_thread_locals, true
-
-    pool << [1] * n
-
-    assert_equal n,  values.length
-
-    assert_equal [], values.compact
-  end
-
   def test_reap_only_dead_threads
     pool = mutex_pool(2,2) do
       th = Thread.current