Generalize SocketLock to account for Chrome port race condition

When the Chrome browser boots up via the Ruby library, it attempts
to find a free port and launch the bridge on that port. However, it's
possible that, if you're running tests in parallel, two bridges will
try to bind to the same port at the same time. This will cause a very
obtuse "end of file" error as documented [here][1].

This patch is based on one initially proposed in the original
[bug report][2]. However, it goes a step further, taking the technical
comments into account, and generalizing the `SocketLock` class used
in the Firefox launcher to assist.

[1]: grosser/parallel_tests#322
[2]: https://code.google.com/p/selenium/issues/detail?id=8241

Signed-off-by: Alexei Barantsev <barancev@gmail.com>

rb/lib/selenium/webdriver/chrome/service.rb

@@ -22,14 +22,12 @@ module Chrome
       #
       # @api private
       #
-
       class Service
-        START_TIMEOUT = 20
-        STOP_TIMEOUT  = 5
-        DEFAULT_PORT  = 9515
-        MISSING_TEXT  = "Unable to find the chromedriver executable. Please download the server from http://chromedriver.storage.googleapis.com/index.html and place it somewhere on your PATH. More info at https://github.com/SeleniumHQ/selenium/wiki/ChromeDriver."
-
-        attr_reader :uri
+        START_TIMEOUT       = 20
+        SOCKET_LOCK_TIMEOUT = 45
+        STOP_TIMEOUT        = 5
+        DEFAULT_PORT        = 9515
+        MISSING_TEXT        = "Unable to find the chromedriver executable. Please download the server from http://chromedriver.storage.googleapis.com/index.html and place it somewhere on your PATH. More info at https://github.com/SeleniumHQ/selenium/wiki/ChromeDriver."
 
         def self.executable_path
           @executable_path ||= (
@@ -47,33 +45,33 @@ def self.executable_path=(path)
         end
 
         def self.default_service(*extra_args)
-          new executable_path, PortProber.above(DEFAULT_PORT), *extra_args
+          new executable_path, DEFAULT_PORT, *extra_args
         end
 
         def initialize(executable_path, port, *extra_args)
-          @uri           = URI.parse "http://#{Platform.localhost}:#{port}"
-          server_command = [executable_path, "--port=#{port}", *extra_args]
+          @executable_path = executable_path
+          @host            = Platform.localhost
+          @port            = Integer(port)
 
-          @process       = ChildProcess.build(*server_command)
-          @socket_poller = SocketPoller.new Platform.localhost, port, START_TIMEOUT
+          raise Error::WebDriverError, "invalid port: #{@port}" if @port < 1
 
-          @process.io.inherit! if $DEBUG == true
+          @extra_args = extra_args
         end
 
         def start
-          @process.start
+          Platform.exit_hook { stop } # make sure we don't leave the server running
 
-          unless @socket_poller.connected?
-            raise Error::WebDriverError, "unable to connect to chromedriver #{@uri}"
+          socket_lock.locked do
+            find_free_port
+            start_process
+            connect_until_stable
           end
-
-          Platform.exit_hook { stop } # make sure we don't leave the server running
         end
 
         def stop
           return if @process.nil? || @process.exited?
 
-          Net::HTTP.start(uri.host, uri.port) do |http|
+          Net::HTTP.start(@host, @port) do |http|
             http.open_timeout = STOP_TIMEOUT / 2
             http.read_timeout = STOP_TIMEOUT / 2
 
@@ -85,8 +83,36 @@ def stop
           # ok, force quit
           @process.stop STOP_TIMEOUT
         end
-      end # Service
 
+        def uri
+          URI.parse "http://#{@host}:#{@port}"
+        end
+
+        def find_free_port
+          @port = PortProber.above @port
+        end
+
+        def start_process
+          server_command = [@executable_path, "--port=#{@port}", *@extra_args]
+          @process       = ChildProcess.build(*server_command)
+
+          @process.io.inherit! if $DEBUG == true
+          @process.start
+        end
+
+        def connect_until_stable
+          @socket_poller = SocketPoller.new @host, @port, START_TIMEOUT
+
+          unless @socket_poller.connected?
+            raise Error::WebDriverError, "unable to connect to chromedriver #{@host}:#{@port}"
+          end
+        end
+
+        def socket_lock
+          @socket_lock ||= SocketLock.new(@port - 1, SOCKET_LOCK_TIMEOUT)
+        end
+
+      end # Service
     end # Chrome
   end # WebDriver
-end # Service
+end # Service

rb/lib/selenium/webdriver/common.rb

@@ -23,6 +23,7 @@
 require 'selenium/webdriver/common/proxy'
 require 'selenium/webdriver/common/log_entry'
 require 'selenium/webdriver/common/file_reaper'
+require 'selenium/webdriver/common/socket_lock'
 require 'selenium/webdriver/common/socket_poller'
 require 'selenium/webdriver/common/port_prober'
 require 'selenium/webdriver/common/zipper'

rb/lib/selenium/webdriver/common/socket_lock.rb

@@ -0,0 +1,76 @@
+# Licensed to the Software Freedom Conservancy (SFC) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The SFC licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+module Selenium
+  module WebDriver
+    class SocketLock
+
+      def initialize(port, timeout)
+        @port    = port
+        @timeout = timeout
+      end
+
+      #
+      # Attempt to acquire a lock on the given port. Control is yielded to an
+      # execution block if the lock could be successfully obtained.
+      #
+
+      def locked(&blk)
+        lock
+
+        begin
+          yield
+        ensure
+          release
+        end
+      end
+
+      private
+
+      def lock
+        max_time = Time.now + @timeout
+
+        until can_lock? || Time.now >= max_time
+          sleep 0.1
+        end
+
+        unless did_lock?
+          raise Error::WebDriverError, "unable to bind to locking port #{@port} within #{@timeout} seconds"
+        end
+      end
+
+      def release
+        @server && @server.close
+      end
+
+      def can_lock?
+        @server = TCPServer.new(Platform.localhost, @port)
+        ChildProcess.close_on_exec @server
+
+        true
+      rescue SocketError, Errno::EADDRINUSE, Errno::EBADF => ex
+        $stderr.puts "#{self}: #{ex.message}" if $DEBUG
+        false
+      end
+
+      def did_lock?
+        !!@server
+      end
+
+    end # SocketLock
+  end # WebDriver
+end # Selenium

rb/lib/selenium/webdriver/firefox.rb

@@ -21,7 +21,6 @@
 
 require 'selenium/webdriver/firefox/util'
 require 'selenium/webdriver/firefox/extension'
-require 'selenium/webdriver/firefox/socket_lock'
 require 'selenium/webdriver/firefox/binary'
 require 'selenium/webdriver/firefox/profiles_ini'
 require 'selenium/webdriver/firefox/profile'