Remove `rack.multithread`/`rack.multiprocess`/`rack.run_once`

These variables generally come too late to be useful. Make `Rack::Lock`
always use a mutex.

Co-authored-by: Samuel Williams <samuel.williams@oriontransfer.co.nz>

13 files changed, 10 insertions, 87 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ed7442d..67a0a27b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,10 @@ All notable changes to this project will be documented in this file. For info on
 
 - Do not use semicolon as GET parameter separator. ([#1733](https://github.com/rack/rack/pull/1733), [@jeremyevans](https://github.com/jeremyevans))
 
+### Removed
+
+- Remove `rack.multithread`/`rack.multiprocess`/`rack.run_once`. These variables generally come too late to be useful. ([#1720](https://github.com/rack/rack/pull/1720), [@ioquatix](https://github.com/ioquatix), [@jeremyevans](https://github.com/jeremyevans)))
+
 ### Added
 
 - `Rack::RewindableInput` supports size. ([@ahorek](https://github.com/ahorek))
diff --git a/SPEC.rdoc b/SPEC.rdoc
index c87cdb6e..6562b2ce 100644
--- a/SPEC.rdoc
+++ b/SPEC.rdoc
@@ -78,19 +78,6 @@ Rack-specific variables:
                            request URL.
 <tt>rack.input</tt>:: See below, the input stream.
 <tt>rack.errors</tt>:: See below, the error stream.
-<tt>rack.multithread</tt>:: true if the application object may be
-                            simultaneously invoked by another thread
-                            in the same process, false otherwise.
-<tt>rack.multiprocess</tt>:: true if an equivalent application object
-                             may be simultaneously invoked by another
-                             process, false otherwise.
-<tt>rack.run_once</tt>:: true if the server expects
-                         (but does not guarantee!) that the
-                         application will only be invoked this one
-                         time during the life of its containing
-                         process. Normally, this will only be true
-                         for a server based on CGI
-                         (or something similar).
 <tt>rack.hijack?</tt>:: present and true if the server supports
                         connection hijacking. See below, hijacking.
 <tt>rack.hijack</tt>:: an object responding to #call that must be
diff --git a/lib/rack.rb b/lib/rack.rb
index b931292e..ad3efec6 100644
--- a/lib/rack.rb
+++ b/lib/rack.rb
@@ -55,9 +55,6 @@ module Rack
   RACK_SESSION                        = 'rack.session'
   RACK_SESSION_OPTIONS                = 'rack.session.options'
   RACK_SHOWSTATUS_DETAIL              = 'rack.showstatus.detail'
-  RACK_MULTITHREAD                    = 'rack.multithread'
-  RACK_MULTIPROCESS                   = 'rack.multiprocess'
-  RACK_RUNONCE                        = 'rack.run_once'
   RACK_URL_SCHEME                     = 'rack.url_scheme'
   RACK_HIJACK                         = 'rack.hijack'
   RACK_IS_HIJACK                      = 'rack.hijack?'
diff --git a/lib/rack/handler/cgi.rb b/lib/rack/handler/cgi.rb
index b514fe74..df0864a1 100644
--- a/lib/rack/handler/cgi.rb
+++ b/lib/rack/handler/cgi.rb
@@ -18,9 +18,6 @@ module Rack
           RACK_VERSION      => Rack::VERSION,
           RACK_INPUT        => Rack::RewindableInput.new($stdin),
           RACK_ERRORS       => $stderr,
-          RACK_MULTITHREAD  => false,
-          RACK_MULTIPROCESS => true,
-          RACK_RUNONCE      => true,
           RACK_URL_SCHEME   => ["yes", "on", "1"].include?(ENV[HTTPS]) ? "https" : "http"
         )
 
diff --git a/lib/rack/handler/webrick.rb b/lib/rack/handler/webrick.rb
index 07c7f9e0..9ce73b40 100644
--- a/lib/rack/handler/webrick.rb
+++ b/lib/rack/handler/webrick.rb
@@ -75,9 +75,6 @@ module Rack
           RACK_VERSION      => Rack::VERSION,
           RACK_INPUT        => rack_input,
           RACK_ERRORS       => $stderr,
-          RACK_MULTITHREAD  => true,
-          RACK_MULTIPROCESS => false,
-          RACK_RUNONCE      => false,
           RACK_URL_SCHEME   => ["yes", "on", "1"].include?(env[HTTPS]) ? "https" : "http",
           RACK_IS_HIJACK    => true,
           RACK_HIJACK       => lambda { raise NotImplementedError, "only partial hijack is supported."},
diff --git a/lib/rack/lint.rb b/lib/rack/lint.rb
index 0d3563b8..fe616138 100755
--- a/lib/rack/lint.rb
+++ b/lib/rack/lint.rb
@@ -166,22 +166,6 @@ module Rack
 
         ## <tt>rack.errors</tt>:: See below, the error stream.
 
-        ## <tt>rack.multithread</tt>:: true if the application object may be
-        ##                             simultaneously invoked by another thread
-        ##                             in the same process, false otherwise.
-
-        ## <tt>rack.multiprocess</tt>:: true if an equivalent application object
-        ##                              may be simultaneously invoked by another
-        ##                              process, false otherwise.
-
-        ## <tt>rack.run_once</tt>:: true if the server expects
-        ##                          (but does not guarantee!) that the
-        ##                          application will only be invoked this one
-        ##                          time during the life of its containing
-        ##                          process. Normally, this will only be true
-        ##                          for a server based on CGI
-        ##                          (or something similar).
-
         ## <tt>rack.hijack?</tt>:: present and true if the server supports
         ##                         connection hijacking. See below, hijacking.
 
@@ -283,8 +267,7 @@ module Rack
         ##
 
         %w[REQUEST_METHOD SERVER_NAME QUERY_STRING
-           rack.version rack.input rack.errors
-           rack.multithread rack.multiprocess rack.run_once].each { |header|
+           rack.version rack.input rack.errors].each { |header|
           raise LintError, "env missing required key #{header}" unless env.include? header
         }
 
diff --git a/lib/rack/lock.rb b/lib/rack/lock.rb
index 4bae3a90..3b084c28 100644
--- a/lib/rack/lock.rb
+++ b/lib/rack/lock.rb
@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'thread'
-
 module Rack
   # Rack::Lock locks every request inside a mutex, so that every request
   # will effectively be executed synchronously.
@@ -12,10 +10,8 @@ module Rack
 
     def call(env)
       @mutex.lock
-      @env = env
-      @old_rack_multithread = env[RACK_MULTITHREAD]
       begin
-        response = @app.call(env.merge!(RACK_MULTITHREAD => false))
+        response = @app.call(env)
         returned = response << BodyProxy.new(response.pop) { unlock }
       ensure
         unlock unless returned
@@ -26,7 +22,6 @@ module Rack
 
     def unlock
       @mutex.unlock
-      @env[RACK_MULTITHREAD] = @old_rack_multithread
     end
   end
 end
diff --git a/lib/rack/mock.rb b/lib/rack/mock.rb
index d9c8a9ce..c4f39b63 100644
--- a/lib/rack/mock.rb
+++ b/lib/rack/mock.rb
@@ -45,9 +45,6 @@ module Rack
       RACK_VERSION      => Rack::VERSION,
       RACK_INPUT        => StringIO.new,
       RACK_ERRORS       => StringIO.new,
-      RACK_MULTITHREAD  => true,
-      RACK_MULTIPROCESS => true,
-      RACK_RUNONCE      => false,
     }.freeze
 
     def initialize(app)
diff --git a/lib/rack/request.rb b/lib/rack/request.rb
index 2df93ebd..1ac50087 100644
--- a/lib/rack/request.rb
+++ b/lib/rack/request.rb
@@ -172,7 +172,6 @@ module Rack
       def content_length;  get_header('CONTENT_LENGTH')                   end
       def logger;          get_header(RACK_LOGGER)                        end
       def user_agent;      get_header('HTTP_USER_AGENT')                  end
-      def multithread?;    get_header(RACK_MULTITHREAD)                   end
 
       # the referer of the client
       def referer;         get_header('HTTP_REFERER')                     end
diff --git a/lib/rack/session/pool.rb b/lib/rack/session/pool.rb
index 849ac885..83a359fb 100644
--- a/lib/rack/session/pool.rb
+++ b/lib/rack/session/pool.rb
@@ -45,7 +45,7 @@ module Rack
       end
 
       def find_session(req, sid)
-        with_lock(req) do
+        @mutex.synchronize do
           unless sid and session = get_session_with_fallback(sid)
             sid, session = generate_sid(use_mutex: false), {}
             @pool.store sid.private_id, session
@@ -55,27 +55,20 @@ module Rack
       end
 
       def write_session(req, session_id, new_session, options)
-        with_lock(req) do
+        @mutex.synchronize do
           @pool.store session_id.private_id, new_session
           session_id
         end
       end
 
       def delete_session(req, session_id, options)
-        with_lock(req) do
+        @mutex.synchronize do
           @pool.delete(session_id.public_id)
           @pool.delete(session_id.private_id)
           generate_sid(use_mutex: false) unless options[:drop]
         end
       end
 
-      def with_lock(req)
-        @mutex.lock if req.multithread?
-        yield
-      ensure
-        @mutex.unlock if @mutex.locked?
-      end
-
       private
 
       def get_session_with_fallback(sid)
diff --git a/test/spec_lock.rb b/test/spec_lock.rb
index 89570498..c86d5b09 100644
--- a/test/spec_lock.rb
+++ b/test/spec_lock.rb
@@ -139,28 +139,6 @@ describe Rack::Lock do
     lock.synchronized.must_equal false
   end
 
-  it "set multithread flag to false" do
-    app = lock_app(lambda { |env|
-      env['rack.multithread'].must_equal false
-      [200, { "Content-Type" => "text/plain" }, %w{ a b c }]
-    }, false)
-    env = Rack::MockRequest.env_for("/")
-    env['rack.multithread'].must_equal true
-    _, _, body = app.call(env)
-    body.close
-    env['rack.multithread'].must_equal true
-  end
-
-  it "reset original multithread flag when exiting lock" do
-    app = Class.new(Rack::Lock) {
-      def call(env)
-        env['rack.multithread'].must_equal true
-        super
-      end
-    }.new(lambda { |env| [200, { "Content-Type" => "text/plain" }, %w{ a b c }] })
-    Rack::Lint.new(app).call(Rack::MockRequest.env_for("/"))
-  end
-
   it 'not unlock if an error is raised before the mutex is locked' do
     lock = Class.new do
       def initialize() @unlocked = false end
@@ -181,7 +159,6 @@ describe Rack::Lock do
     end
     app = Rack::Lock.new lambda { |env| [200, { "Content-Type" => "text/plain" }, proxy.new(env)] }
     response = app.call(Rack::MockRequest.env_for("/"))[2]
-    response.env['rack.multithread'].must_equal false
   end
 
   it "unlock if an exception occurs before returning" do
diff --git a/test/spec_session_pool.rb b/test/spec_session_pool.rb
index e7ed3143..a8e1f3da 100644
--- a/test/spec_session_pool.rb
+++ b/test/spec_session_pool.rb
@@ -241,7 +241,7 @@ describe Rack::Session::Pool do
     tnum = rand(7).to_i + 5
     r = Array.new(tnum) do
       Thread.new(treq) do |run|
-        run.get('/', "HTTP_COOKIE" => cookie, 'rack.multithread' => true)
+        run.get('/', "HTTP_COOKIE" => cookie)
       end
     end.reverse.map{|t| t.run.join.value }
     r.each do |resp|
diff --git a/test/spec_webrick.rb b/test/spec_webrick.rb
index d67dd35f..ffb03740 100644
--- a/test/spec_webrick.rb
+++ b/test/spec_webrick.rb
@@ -50,9 +50,6 @@ describe Rack::Handler::WEBrick do
   it "have rack headers" do
     GET("/test")
     response["rack.version"].must_equal [1, 3]
-    response["rack.multithread"].must_equal true
-    assert_equal false, response["rack.multiprocess"]
-    assert_equal false, response["rack.run_once"]
   end
 
   it "have CGI headers on GET" do