Tema 1. Comunicación entre. Procesos, Sockets

Transcripción

1 Tema 1 1 Comunicación entre Procesos, Sockets 2

2 Objetivos Conceptos Básicos: sincronización IPC, direcciones y puertos, Paradigmas IPC. IPC sin conexión: Sockets Datagrama. IPC orientada conexión: Sockets Stream. 3 IPC Sistema Distribuido vs. Sistema Operativo. - La computación distribuida require intercambio de información entre procesos independientes. - Los sistemas operativos proveen mecanismos para la comunicación entre procesos (IPC), como señales, tuberias, colas de mensajes, streams, semaforos y memoria compartida. - Para los sistemas distribuidos se intentan diseñar mecanismos que provean el mismo Interface de Programación de Aplicaciones (API): - Transparencia de localización: (enviar mensaje local = enviar mensaje remoto) - No es necesario reprogramar las aplicaciones. 4

3 Sincronización en IPC IPC require la sincronización de las operaciones de los dos procesos: una parte envia, entonces la otra parte recibe hasta que todos los datos hayan sido enviados y recibidos. Idealmente, la operación enviar comienzo antes que la operación recibir. Send() Receive() Send() Process A mensaje 1 Process B Receive() time interprocess communication execution flow IPC Ideal 5 Envio asincrono (no-bloqueante) recepción sincrona (bloqueante) Las operaciones IPC proveen la sincronización necesaria utilizando bloqueo: Una operación bloqueante bloqueara su proceso hasta que haya finalizado. Las operaciones IPC tambien pueden ser asincronas o nobloqueantes. Una operación asincrona no bloqueara el procesamiento de más instrucciones del proceso. El proceso es libre de seguir procesando, y puede opcionalmente ser notificado por el sistema cuando la operación haya finalizado. Send() non-bloking Receive() bloking Send() Process A request 1 Process B Receive() time interprocess communication execution flow process blocked Eventos en IPC paso de mensajes 6

4 Deadlocks y timeouts Operaciones bloqueantes efectuadas en un orden incorrecto pueden pueden causar deadlocks.(abrazo mortal). Los deadlocks deben de ser evitados. No es aceptable que un proceso espere indefinidamente. Los bloqueos indefinidos se evitan usando timeout. Process 1 Process 2 Receive() receive from process 2 issued process 1 blocked pending data from process 2. SetTimeout(3) Receive() received from process 1 issued process 2 blocked pending data from process 1. Timeout() 7 Direcciones y Puertos Destino de mensajes se define por: una dirección IP (o un nombre DNS) y un puerto. Un puerto es un destino en un ordenador. Cada ordenador tiene multiples puertos: 2 16 (65,535). Los puertos numerados entre el 1 y 1023 estan reservados para procesos que proveen servicios conocidos: finger, FTP, HTTP, and . Cada proceso puede enviar y recibir por multiples puertos. Proc1 any port agreed port Proc1 Proc2 message other ports Proc7 Internet address = Internet address =

5 Paradigmas IPC Hay diferentes mecanismos de IPC con diferentes niveles de abstracción. Los mecanismos de IPC se construyen unos sobre otros. Los mecanismos superiores simplifican la programación de las aplicaciones. level of abstraction IPC paradigms Example IPC Implementations remote procedure/method Petición-Respuesta RMI Sockets socket Paso mensajes Datagramas 9 Paso de Mensajes Paradigma IPC más sencillo. Sobre él se construyen otros IPC. (Implementaciones: Paquetes IP, Datagramas.) Process 1 Process 2 Primitivas: SEND([receiver],message) data RECEIVE([sender], message storage object). sender receiver 10

6 Datagramas: emisor mysocket.send(datagram); mysocket.close( ); } // end try catch (Exception ex) { ex.printstacktrace( ); receptor emisor } } // end else } // end main DataGramSocket.receive() } // end class datagram DataGramSocket.send() 11 Datagramas: receptor import java.net.*; import java.io.*; public class Example1Receiver { public static void main(string[] args) { if (args.length!= 1) System.out.println ("This program requires a command line argument."); else { int port = Integer.parseInt(args[0]); final int MAX_LEN = 10; // This is the assumed maximum byte length try { DatagramSocket mysocket = new DatagramSocket(port); byte[ ] buffer = new byte[max_len]; DatagramPacket datagram = new DatagramPacket(buffer, MAX_LEN); mysocket.receive(datagram); String message = new String(buffer); System.out.println(message); mysocket.close( ); } // end try catch (Exception ex) { ex.printstacktrace( );} } // end else } // end main } // end class // instantiates a datagram socket for receiving the data receptor emisor DataGramSocket.receive() datagram DataGramSocket.send() 12

7 Envio-Recepción varios datagramas. import java.net.*; import java.io.*; public class Example1Sender { public static void main(string[] args) { try { InetAddress receiverhost = InetAddress.getByName(args[0]); int receiverport = Integer.parseInt(args[1]); String message = args[2]; // instantiates a datagram socket for sending the data DatagramSocket mysocket = new DatagramSocket(); byte[ ] buffer = message.getbytes( ); DatagramPacket datagram = new DatagramPacket(buffer, buffer.length, receiverhost, receiverport); mysocket.send(datagram); mysocket.send(datagram); mysocket.send(datagram); mysocket.send(datagram); Receptor?? emisor mysocket.close( ); } // end try catch (Exception ex) { ex.printstacktrace( ); } } // end else } // end main } // end class datagram datagram datagram datagram DataGramSocket.send() DataGramSocket.send() DataGramSocket.send() DataGramSocket.send() 13 Transmisión con Datagramas server client DataGramSocket.receive() blocking receive, nonblocking send blocked Recibido: Data1 Data 3 Data 2 DataGramSocket.receive() DataGramSocket.receive() DataGramSocket.receive() data1 data3 data2 data4 DataGramSocket.send() DataGramSocket.send() DataGramSocket.send() DataGramSocket.send() Enviado: Data1 Data 2 Data 3 Data 4 if data is sent before a corresponding receive operation is issued, the data will be discarded by the runtime support and will not be received. 14

8 Socket Datagrama en JAVA Method/Constructor DatagramPacket(byte[ ] buf, int length) DatagramPacket (byte[ ] buf, int length, InetAddress address, int port) DatagramSocket ( ) DatagramSocket (int port) void close( ) void receive(datagrampacket p) Description Construct a datagram packet for receiving packets of length length; data received will be stored in the byte array reference by buf. Construct a datagram packet for sending packets of length length to the socket bound to the specified port number on the specified host ; data received will be stored in the byte array reference by buf. Construct a datagram socket and binds it to any available port on the local host machine; this constructor can be used for a process that sends data and does not need to receive data. Construct a datagram socket and binds it to the specified port on the local host machine; the port number can then be specified in a datagram packet sent by a sender. Close this datagramsocket object Receive a datagram packet using this socket. void send (DatagramPacket p) void setsotimeout(int timeout) Send a datagram packet using this socket. Set a timeout for the blocking receive from this socket, in milliseconds. 15 IPC sin / con conexión socket API runtime support Process A Process B socket API runtime support transport layer software transport layer software connectionless datagram socket a datagram a logical connection created and maintained by the runtime support of the datagram socket API socket API runtime support Process A Process B socket API runtime support transport layer software transport layer software connection-oriented datagram socket 16

9 Socket con conexión: Stream-mode Socket API P1 a stream-mode data socket process write operation read operation P a data stream Los Stream Sockets: no descartan mensajes, Entregan al proceso los datos ordenados. Se puede leer y escribir de un mismo socket (con 2 streams como el en SO) 17 Establecimiento Conexión (I) Cada servidor utilizan dos sockets para establecer conexiones. 1. Servidor crea socket de conexión y se pone a la escucha de conexión: Listener Connection socket Requester 2. Un cliente crea un socket con la dirección del servidor remoto. 3. El servidor accepta la conexión y crea un nuevo socket de datos (en otro puerto) Connection socket Data socket 4. El cliente es informado del puerto del data socket. 18

10 Establecimiento Conexión (II) 5. El servidor realiza una operación receive en el socket de datos. 7. El servidor responde por el socket de datos. 9. Cuando acaba el protocolo, el servidor cierra el socket de datos. El socket de conexión puede seguir recibiendo conexiones. Connection socket Data socket Connection socket Data socket Connection socket 6. El cliente realiza una operación send. A continuación realiza un receive. 8. El cliente recibe los datos del servidor. 10. El cliente cierra su socket cuando el protocolo ha completado. Los pasos 5,6,7,8 podrían ir en otro orden, cuando el servidor envia datos en primer lugar (como en ejemplo Example4Connection Acceptor.java) 19 Flujo de programas conectado por Sockets en modo stream connection listener (server) create a connection socket and listen for connection requests; accept a connection; creates a data socket for reading from or writing to the socket stream; get an input stream for reading to the socket; read from the stream; get an output stream for writing to the socket; write to the stream; close the data socket; close the connection socket. connection requester (client) create a data socket and request for a connection; get an output stream for writing to the socket; write to the stream; get an input stream for reading to the socket; read from the stream; close the data socket. 20

11 The Stream-mode Socket API El API de sockets datagramas solo soporta el intercambio de unidades sencillas de datos, los datagramas. El API stream socket provee un modo de transferencia basado en los streams de I/O del sistema operativo Unix: 1 socket en cada extremo con 2 streams: out e in. Por definición, un socket en modo streams soporta solo comunicaciones con conexión. Un socket stream se establece entre dos procesos especificos. Un socket stream no puede utilizarse para comunicar con más de un proceso (hay que utilizar varios sockets). 21 import java.net.*; import java.io.*; public class Example4ConnectionAcceptor { public static void main(string[] args) { if (args.length!= 2) System.out.println ("This program requires two command line arguments"); else { try { int portno = Integer.parseInt(args[0]); String message = args[1]; // instantiates a socket for accepting connection ServerSocket connectionsocket = new ServerSocket(portNo); /**/ System.out.println("Now ready to accept a connection"); // wait to accept a connecion request, at which time a data socket is created Socket datasocket = connectionsocket.accept(); /**/ System.out.println("connection accepted"); // get a output stream for writing to the data socket OutputStream outstream = datasocket.getoutputstream(); // create a PrinterWriter object for character-mode output PrintWriter socketoutput = new PrintWriter(new OutputStreamWriter(outStream)); // write a message into the data stream socketoutput.println(message); //The ensuing flush method call is necessary for // the data to be written to the socket data //stream before the socket is closed. socketoutput.flush(); /**/ System.out.println("message sent"); datasocket.close( ); /**/ System.out.println("data socket closed"); connectionsocket.close( ); /**/ System.out.println("connection socket closed"); } // end try catch (Exception ex) { ex.printstacktrace( ); } //end catch } // end else } // end main } // end class connection socket accept ConnectionAcceptor data socket write close close connect message ConnectionRequestor close socket connect request (from Socket constru read 22

12 import java.net.*; import java.io.*; public class Example4ConnectionRequestor { public static void main(string[] args) { if (args.length!= 2) System.out.println ("This program requires two command line arguments"); else { try { InetAddress acceptorhost = InetAddress.getByName(args[0]); int acceptorport = Integer.parseInt(args[1]); // instantiates a data socket Socket mysocket = new Socket(acceptorHost, acceptorport); /**/ System.out.println("Connection request granted"); // get an input stream for reading from the data socket InputStream instream = mysocket.getinputstream(); // create a BufferedReader object for text line input BufferedReader socketinput = new BufferedReader(new InputStreamReader(inStream)); /**/ System.out.println("waiting to read"); // read a line from the data stream String message = socketinput.readline( ); /**/ System.out.println("Message received:"); System.out.println("\t" + message); mysocket.close( ); /**/ System.out.println("data socket closed"); } // end try catch (Exception ex) { ex.printstacktrace( ); } //end catch } // end else } // end main } // end class connection socket accept ConnectionAcceptor data socket write close connect message ConnectionRequestor connect request (from Socket constructo read close close socket 23 JAVA Stream Socket API (I) Java provee dos clases para sockets en modo stream: Server socket:para aceptar conexiones (conexion socket) Socket: para intercambiar datos (Data socket) for data exchange; we will call an object of this class a data socket. Metodos de ServerSocket: M ethod/constructor ServerSocket(int port) Socket accept() throw s IO E xception public void close() throw s IO E xception void setsot im eout(int tim eout) throw s SocketE xception D escription C reates a server socket on a specified port. Listens for a connection to be m ade to this socket and accepts it. T he m ethod blocks until a connection is m ade. C loses this socket. Set a tim eout period (in m illiseconds) so that a call to accept( ) for this socket w ill block for only this am ount of tim e. If the tim eout expires, a java.io.interruptedio E xception is raised Note: Accept is a blocking operation. 24

13 JAVA Stream Socket API (II) Metodos de Socket: Method/constructor Socket(InetAddress address, int port) void close() throws IOException InputStream getinputstream( ) throws IOException OutputStream getoutputstream( )throws IOException Description Creates a stream socket and connects it to the specified port number at the specified IP address Closes this socket. Returns an input stream so that data may be read from this socket. Returns an output stream so that data may be written to this socket. void setsotimeout(int timeout) throws SocketException Set a timeout period for blocking so that a read( ) call on the InputStream associated with this Socket will block for only this amount of time. If the timeout expires, a java.io.interruptedioexception is raised A read operation on the InputStream is blocking. A write operation is nonblocking. 25 Protocolo HTTP 26

14 Protocolos - En un sistema distribuido, dos o más procesos establecen comunicación IPC en un protocolo acordado por los procesos. Un proceso será emisor en algunos instantes del protocolo, y receptor en otros momentos. Las especificaciones de un protocolo deben incluir: (i) la sequencia del intercambio de datos, que se puede describir usando un diagrama de eventos en el tiempo. (ii) las especificaciones del formato de datos intercambiado en cada paso. 27 Protocolo HTTP Protocolo de nivel aplicación sobre stream sockets. Datos en formato texto. Basado en paradigma request/response. FORMATO DE DATOS Request: METODO URL VERSION Metodo=GET POST PUT Response: STATUS HEADERS BODY STATUS= Web Client DIAGRAMA DE EVENTOS Request Response Web Server time 28

15 A sample HTTP session (telnet version) Web Client: Iexplorer, FireFox, Telnet,. GET /index.html HTTP/1.0 Server host $ telnet 80 Trying Connected to tiedye2-srv.csc.calpoly.edu. Escape character is '^]'. GET /index.html HTTP/1.0 HTTP/ OK Date: Wed, 11 Oct :51:18 GMT Server: Apache/1.3.9 (Unix) ApacheJServ/1.0 Last-Modified: Tue, 10 Oct :51:54 GMT ETag: "1dd1e-e27-39e3492a" Accept-Ranges: bytes Content-Length: 3623 Connection: close Content-Type: text/html <HTML> <HEAD> <TITLE> Mei-Ling L. Liu's Home Page </TITLE> </HEAD> <BODY bgcolor=#ffffff> HTTP/ OK Date: Wed, 11 Oct :51:18 GMT Server: Apache/1.3.9 (Unix) ApacheJServ/1.0 Last-Modified: Tue, 10 Oct :51:54 GMT ETag: "1dd1e-e27-39e3492a" Accept-Ranges: bytes Content-Length: 3623 Connection: close Content-Type: text/html <HTML> <HEAD> <TITLE> Mei-Ling L. Liu's Home Page </TITLE> </HEAD> <BODY bgcolor=#ffffff> 29 import java.net.*; import java.io.*; public class HTTPClient { public static void main(string[] args) { if (args.length!= 3) System.out.println ("This program requires 3 command line arguments"); else { try { InetAddress host = InetAddress.getByName(args[0]); int port = Integer.parseInt(args[1]); String filename = args[2].trim(); String request = "GET " + filename + " HTTP/1.0\n\n"; MyStreamSocket mysocket = new MyStreamSocket(host, port); /**/ System.out.println("Connection made"); mysocket.sendmessage(request); Send() Receive() Process A GET filename HTTP/1.0\n\n Process B // now receive the response from the HTTP server String response; response = mysocket.receivemessage(); // read and display one line at a time while (response!= null) { System.out.println(response); response = mysocket.receivemessage(); } } // end try catch (Exception ex) { System.out.println("ERROR : " + ex) ; ex.printstacktrace(system.out); } // end catch }// end else }// end main } //end class Receive() Receive() response 1\r\n response2\r\n response3\n\n 30

16 HTTP Requests ~ GET: for retrieving the contents of web object referenced by the specified URI ~ HEAD: for retrieving a header from the server only, not the object itself. ~ POST: used to send data to a process on the server host. ~ PUT: used to request the server to store the contents enclosed with the request to the server machine in the file location specified by the URI. Request Example: POST /servlet/myserver.servlet HTTP/1.0 Host: somehost.com User-Agent: Generic <blank line> Name=donald& =donald@someU.edu 31 HTTP Responses The status code designations are as follows: Informational Client request successful Client request redirected Client request incomplete Server errors Response Example: HTTP/ OK Date: Sat, 15 Sep :55:30 GMT Server: Apache/1.3.9 (Unix) ApacheJServ/1.0 Last-Modified: Mon, 30 Apr :02:36 GMT Content-Length: 236 Content-Type: text/html <html> <head> <title>my web page </title> </head> <body> Hello world! </BODY></HTML> 32

17 Java URL Class Representa un Universal Resource Locator: protocolo dirección puerto camino +nombre fichero Method/Constructor Description URL(String spec) Creates a URL object from the URL name contained in a String URL(String protocol, String host, int port,string file) Creates a URL object from the specified protocol, host, port number, and file. URLConnection openconnection() InputStream openstream() Returns a URLConnection object that represents a connection to the remote object referred to by the URL. Opens a connection to this URL and returns an InputStream for reading from that connection. Equivante to: openconnection().getinputstream() 33 import java.net.*; import java.io.*; public class URLBrowser { public static void main(string[] args) { if (args.length!= 3) System.out.println ("This program requires 3 command line arguments"); else { try { String host = args[0]; String port = args[1].trim(); String filename = args[2].trim(); String HTTPString = " URL theurl = new URL(HTTPString); InputStream instream = theurl.openstream( ); BufferedReader input = new BufferedReader (new InputStreamReader(inStream)); String response; response = input.readline(); // read and display one line at a time while (response!= null) { System.out.println(response); response = input.readline(); } //end while } catch (Exception ex) { } }// end else }// end main } //end class 34

18 URLConnection / HttpURLConnection URLConnection: Representa a connection to a URL. Method/Constructor Description connect() Opens a communications link to the resource referenced by this URL, if such a connection has not already been established String getheaderfield (String name) Returns the value of the named header field. HttpURLConnection Sub-clases de la anterior. Contiene métodos específicos para conexiones HTTP. Method/Constructor setrequestmethod(string method) Description Set the method for the URL request, one of: GET POST HEAD OPTIONS PUT DELETE TRACE are legal, subject to protocol restrictions. int getresponsecode() Gets the status code from an HTTP response message. 35