socket_manager: add feature to share sockets with another server

README.md

@@ -413,8 +413,15 @@ se = ServerEngine.create(MyServer, MyWorker, {
 se.run
 ```
 
-See also [examples](https://github.com/fluent/serverengine/tree/master/examples).
+Other features:
+
+- `socket_manager_server = SocketManager::Server.share_sockets_with_another_server(path)`
+  - It starts a new manager server that shares all UDP/TCP sockets with the existing manager.
+  - We can use this for live restart for network servers.
+  - The old process should stop without removing the file for the socket after the new process starts.
+  - Limitation: This feature would not work well if the process opens new TCP ports frequently.
 
+See also [examples](https://github.com/fluent/serverengine/tree/master/examples).
 
 ## Module API
 

lib/serverengine/socket_manager.rb

@@ -96,19 +96,32 @@ def self.open(path = nil)
         end
       end
 
-      def initialize(path)
+      def self.share_sockets_with_another_server(path)
+        raise NotImplementedError, "Not supported on Windows." if ServerEngine.windows?
+        server = new(path, start: false)
+        server.share_sockets_with_another_server
+        server
+      end
+
+      def initialize(path, start: true)
         @tcp_sockets = {}
         @udp_sockets = {}
         @mutex = Mutex.new
-        @path = start_server(path)
+        @path = start ? start_server(path) : path
       end
 
       attr_reader :path
+      attr_reader :tcp_sockets, :udp_sockets # for tests
 
       def new_client
         Client.new(@path)
       end
 
+      def start
+        start_server(path)
+        nil
+      end
+
       def close
         stop_server
         nil
@@ -159,9 +172,9 @@ def process_peer(peer)
           res = SocketManager.recv_peer(peer)
           return if res.nil?
 
-          pid, method, bind, port = *res
+          pid, method, *opts = res
           begin
-            send_socket(peer, pid, method, bind, port)
+            send_socket(peer, pid, method, *opts)
           rescue => e
             SocketManager.send_peer(peer, e)
           end

lib/serverengine/socket_manager_unix.rb

@@ -47,6 +47,38 @@ def recv_udp(family, peer, sent)
     end
 
     module ServerModule
+      def share_sockets_with_another_server
+        another_server = UNIXSocket.new(@path)
+        begin
+          idx = 0
+          while true
+            SocketManager.send_peer(another_server, [Process.pid, :share_udp, idx])
+            key = SocketManager.recv_peer(another_server)
+            break if key.nil?
+            @udp_sockets[key] = another_server.recv_io UDPSocket
+            idx += 1
+          end
+
+          idx = 0
+          while true
+            SocketManager.send_peer(another_server, [Process.pid, :share_tcp, idx])
+            key = SocketManager.recv_peer(another_server)
+            break if key.nil?
+            @tcp_sockets[key] = another_server.recv_io TCPServer
+            idx += 1
+          end
+
+          SocketManager.send_peer(another_server, [Process.pid, :share_unix])
+          res = SocketManager.recv_peer(another_server)
+          raise res if res.is_a?(Exception)
+          @server = another_server.recv_io UNIXServer
+
+          start_server(@path)
+        ensure
+          another_server.close
+        end
+      end
+
       private
 
       def listen_tcp_new(bind_ip, port)
@@ -77,15 +109,17 @@ def listen_udp_new(bind_ip, port)
       end
 
       def start_server(path)
-        # return absolute path so that client can connect to this path
-        # when client changed working directory
-        path = File.expand_path(path)
+        unless @server
+          # return absolute path so that client can connect to this path
+          # when client changed working directory
+          path = File.expand_path(path)
 
-        begin
-          old_umask = File.umask(0077) # Protect unix socket from other users
-          @server = UNIXServer.new(path)
-        ensure
-          File.umask(old_umask)
+          begin
+            old_umask = File.umask(0077) # Protect unix socket from other users
+            @server = UNIXServer.new(path)
+          ensure
+            File.umask(old_umask)
+          end
         end
 
         @thread = Thread.new do
@@ -111,19 +145,34 @@ def stop_server
         @thread.join if RUBY_VERSION >= "2.2"
       end
 
-      def send_socket(peer, pid, method, bind, port)
-        sock = case method
-               when :listen_tcp
-                 listen_tcp(bind, port)
-               when :listen_udp
-                 listen_udp(bind, port)
-               else
-                 raise ArgumentError, "Unknown method: #{method.inspect}"
-               end
-
-        SocketManager.send_peer(peer, nil)
-
-        peer.send_io sock
+      def send_socket(peer, pid, method, *opts)
+        case method
+        when :listen_tcp
+          bind, port = opts
+          sock = listen_tcp(bind, port)
+          SocketManager.send_peer(peer, nil)
+          peer.send_io sock
+        when :listen_udp
+          bind, port = opts
+          sock = listen_udp(bind, port)
+          SocketManager.send_peer(peer, nil)
+          peer.send_io sock
+        when :share_tcp
+          idx, = opts
+          key = @tcp_sockets.keys[idx]
+          SocketManager.send_peer(peer, key)
+          peer.send_io(@tcp_sockets.values[idx]) if key
+        when :share_udp
+          idx, = opts
+          key = @udp_sockets.keys[idx]
+          SocketManager.send_peer(peer, key)
+          peer.send_io(@udp_sockets.values[idx]) if key
+        when :share_unix
+          SocketManager.send_peer(peer, nil)
+          peer.send_io @server
+        else
+          raise ArgumentError, "Unknown method: #{method.inspect}"
+        end
       end
     end
 

spec/socket_manager_spec.rb

@@ -55,6 +55,15 @@
         expect(server.path).to be_between(49152, 65535)
       end
     end
+
+    context 'Server.share_sockets_with_another_server' do
+      it 'not supported' do
+        server = SocketManager::Server.open(server_path)
+        expect { SocketManager::Server.share_sockets_with_another_server(server_path) }.to raise_error(NotImplementedError)
+      ensure
+        server.close
+      end
+    end
   else
     context 'Server.generate_path' do
       it 'returns socket path under /tmp' do
@@ -76,6 +85,165 @@
         expect(server.path).to include('/tmp/SERVERENGINE_SOCKETMANAGER_')
       end
     end
+
+    context 'Server.share_sockets_with_another_server' do
+      it 'shares listen sockets to another server' do
+        server = SocketManager::Server.open(server_path)
+
+        client = SocketManager::Client.new(server_path)
+        tcp1 = client.listen_tcp('127.0.0.1', 55551)
+        udp1 = client.listen_udp('127.0.0.1', 55561)
+        udp2 = client.listen_udp('127.0.0.1', 55562)
+
+        another_server = SocketManager::Server.share_sockets_with_another_server(server_path)
+
+        expect([
+          another_server.tcp_sockets.keys,
+          another_server.tcp_sockets.values.map(&:addr),
+          another_server.udp_sockets.keys,
+          another_server.udp_sockets.values.map(&:addr),
+        ]).to eq([
+          server.tcp_sockets.keys,
+          server.tcp_sockets.values.map(&:addr),
+          server.udp_sockets.keys,
+          server.udp_sockets.values.map(&:addr),
+        ])
+      ensure
+        tcp1&.close
+        udp1&.close
+        udp2&.close
+        server&.close
+        another_server&.close
+      end
+
+      it 'takes over TCP sockets without downtime' do
+        manager_server = SocketManager::Server.open(server_path)
+        manager_client = SocketManager::Client.new(server_path)
+
+        has_server_started = false
+        # The old server starts listening
+        thread_server = Thread.new do
+          server = manager_client.listen_tcp('127.0.0.1', test_port)
+          has_server_started = true
+          while socket = server.accept
+            incr_test_state(:count)
+            socket.close
+          end
+        ensure
+          server&.close
+        end
+
+        sleep 0.1 until has_server_started
+
+        # The client starts sending data
+        thread_client = Thread.new do
+          100.times do |i|
+            socket = TCPSocket.new('127.0.0.1', test_port)
+            begin
+              socket.write("Hello #{i}\n")
+            ensure
+              socket.close
+            end
+            sleep 0.01
+          end
+        end
+
+        sleep 0.5
+
+        # The new server shares the sockets and starts listening in parallel with the old one
+        thread_new_server = Thread.new do
+          new_manager_server = SocketManager::Server.share_sockets_with_another_server(server_path)
+          server = manager_client.listen_tcp('127.0.0.1', test_port)
+          while socket = server.accept
+            incr_test_state(:count)
+            socket.close
+          end
+        ensure
+          new_manager_server&.close
+          server&.close
+        end
+
+        # Stop the old server
+        sleep 0.1
+        thread_server.kill
+        thread_server.join
+
+        thread_client.join
+        wait_for_stop
+
+        # Confirm that server switching was completed without data loss
+        expect(test_state(:count)).to eq(100)
+      ensure
+        manager_server&.close
+        thread_server&.kill
+        thread_new_server&.kill
+        thread_server&.join
+        thread_new_server&.join
+      end
+
+      it 'takes over UDP sockets without downtime' do
+        manager_server = SocketManager::Server.open(server_path)
+        manager_client = SocketManager::Client.new(server_path)
+
+        has_server_started = false
+        # The old server starts listening
+        thread_server = Thread.new do
+          server = manager_client.listen_udp('127.0.0.1', test_port)
+          has_server_started = true
+          while server.recv(10)
+            incr_test_state(:count)
+          end
+        ensure
+          server&.close
+        end
+
+        sleep 0.1 until has_server_started
+
+        # The client starts sending data
+        thread_client = Thread.new do
+          100.times do |i|
+            socket = UDPSocket.new
+            begin
+              socket.send("Hello #{i}\n", 0, "127.0.0.1", test_port)
+            ensure
+              socket.close
+            end
+            sleep 0.01
+          end
+        end
+
+        sleep 0.5
+
+        # The new server shares the sockets and starts listening in parallel with the old one
+        thread_new_server = Thread.new do
+          new_manager_server = SocketManager::Server.share_sockets_with_another_server(server_path)
+          server = manager_client.listen_udp('127.0.0.1', test_port)
+          while server.recv(10)
+            incr_test_state(:count)
+          end
+        ensure
+          new_manager_server&.close
+          server&.close
+        end
+
+        # Stop the old server
+        sleep 0.1
+        thread_server.kill
+        thread_server.join
+
+        thread_client.join
+        wait_for_stop
+
+        # Confirm that server switching was completed without data loss
+        expect(test_state(:count)).to eq(100)
+      ensure
+        manager_server&.close
+        thread_server&.kill
+        thread_new_server&.kill
+        thread_server&.join
+        thread_new_server&.join
+      end
+    end
   end
 
   context 'with thread' do