Tema 1. Comunicación entre Procesos, Sockets

Transcripción

1 Tema 1 Comunicación entre Procesos, Sockets 1 2 Objetivos Conceptos Básicos: sincronización IPC, direcciones y puertos, Paradigmas IPC. IPC sin conexión: Sockets Datagrama. IPC orientada conexión: Sockets Stream. 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. 3 4

2 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. 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() Send() mensaje 1 time Send() non-bloking bloking Send() request 1 time interprocess communication execution flow IPC Ideal 5 interprocess communication execution flow process blocked Eventos en IPC paso de mensajes 6 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. receive from process 2 issued process 1 blocked pending data from process 2. Process 1 Process 2 SetTimeout(3) 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 Proc2 Internet address = any port message other ports agreed port Proc1 Proc7 Internet address =

3 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 remote procedure/method Cliente- Servidor Paso mensajes Example IPC Implementations RMI Sockets Datagramas Paso de Mensajes Paradigma IPC más sencillo. Sobre él se construyen otros IPC. (Implementaciones: Paquetes IP, Datagramas.) Primitivas: SEND([receiver],message) RECEIVE([sender], message storage object). Process 1 Process 2 sender data receiver 9 10 Datagramas: emisor public class Example1Sender { if (args.length!= 3) System.out.println ("This program requires three command line arguments"); InetAddress receiverhost = InetAddress.getByName(args[0]); int receiverport = Integer.parseInt(args[1]); String message = args[2]; // instantiates a for sending the data DatagramSocket mysocket = new DatagramSocket(); byte[ ] buffer = message.getbytes( ); DatagramPacket = new DatagramPacket(buffer, buffer.length, receiverhost, receiverport); mysocket.send(); mysocket.close( ); catch (Exception ex) { receptor emisor ex.printstacktrace( ); // end main // end class Datagramas: receptor public class Example1Receiver { if (args.length!= 1) System.out.println ("This program requires a command line argument."); int port = Integer.parseInt(args[0]); final int MAX_LEN = 10; // This is the assumed maximum byte length // instantiates a for receiving the data DatagramSocket mysocket = new DatagramSocket(port); byte[ ] buffer = new byte[max_len]; DatagramPacket = new DatagramPacket(buffer, MAX_LEN); mysocket.receive(); String message = new String(buffer); System.out.println(message); mysocket.close( ); catch (Exception ex) { ex.printstacktrace( ); // end main receptor emisor // end class 11 12

4 Envio-Recepción varios as. public class Example1Sender { InetAddress receiverhost = InetAddress.getByName(args[0]); int receiverport = Integer.parseInt(args[1]); String message = args[2]; // instantiates a for sending the data DatagramSocket mysocket = new DatagramSocket(); byte[ ] buffer = message.getbytes( ); DatagramPacket = new DatagramPacket(buffer, buffer.length, receiverhost, receiverport); mysocket.send(); mysocket.send(); mysocket.send(); mysocket.send(); mysocket.close( ); catch (Exception ex) { ex.printstacktrace( ); // end main // end class Receptor?? emisor Transmisión con Datagramas Recibido: Data1 Data 3 Data 2 server data1 data3 data2 data4 client blocking receive, nonblocking send blocked 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 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) void send (DatagramPacket p) void setsotimeout(int timeout) Construct a packet for receiving packets of length length; data received will be stored in the byte array reference by buf. Construct a packet for sending packets of length length to the bound to the specified port number on the specified host ; data received will be stored in the byte array reference by buf. Construct a 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 and binds it to the specified port on the local host machine; the port number can then be specified in a packet sent by a sender. Close this Socket object Receive a packet using this. Send a packet using this. Set a timeout for the blocking receive from this, in milliseconds. IPC sin / con conexión API runtime support API runtime support transport layer software transport layer software connectionless API runtime support transport layer software a a logical connection created and maintained by the runtime support of the API API runtime support transport layer software 15 connection-oriented 16

5 Socket con conexión: Stream-mode Socket API P1 process a stream-mode data write operation read operation P2 Establecimiento Conexión Cada servidor utilizan dos s para establecer conexiones. 1. Servidor crea de conexión y se pone a la escucha de conexión: Listener Requester 2. Un cliente crea un con la dirección del servidor remoto. a data stream Los Stream Sockets: no descartan mensajes, Entregan al proceso los datos ordenados. Se puede leer y escribir en un mismo (con 2 stream, como en el SO) El servidor accepta la conexión y crea un nuevo de datos. Data 4. El cliente es informado del puerto del data. 18 Envio/Recepción Datos 5. El servidor realiza una operación receive en el de datos. 7. El servidor responde por el de datos. 9. Cuando acaba el protocolo, el servidor cierra el de datos. El de conexión puede seguir recibiendo conexiones. Data Data 6. El cliente realiza una operación send. Y el cliente realiza un receive. 8. Recibe los datos del servidor. 10. El cliente cierra su cuando el protocolo ha completado. Flujo de programas conectado por Sockets en modo stream connection listener (server) create a connection and listen for connection requests; accept a connection; creates a data for reading from or writing to the stream; get an input stream for reading to the ; read from the stream; get an output stream for writing to the ; write to the stream; close the data ; close the connection. connection requester (client) create a data and request for a connection; get an output stream for writing to the ; write to the stream; get an input stream for reading to the ; read from the stream; close the data. 5,6,7,8 podrian ser al revés, servidor envia y cliente recibe (ver ejemplo Example4Acceptor y Example4Requestor) 19 20

6 The Stream-mode Socket API El API de s as solo soporta el intercambio de unidades sencillas de datos, los as. El API stream provee un modo de transferencia basado en los streams de I/O del sistema operativo Unix: 1 en cada extremo con 2 streams: out e in. Por definición, un en modo streams soporta solo comunicaciones con conexión. Un stream se establece entre dos procesos especificos. Un stream no puede utilizarse para comunicar con más de un proceso (hay que utilizar varios s). 21 public class Example4Acceptor { if (args.length!= 2) System.out.println ("This program requires two command line arguments"); int portno = Integer.parseInt(args[0]); String message = args[1]; // instantiates a 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 is created Socket datasocket = connectionsocket.accept(); /**/ System.out.println("connection accepted"); // get a output stream for writing to the data OutputStream outstream = datasocket.getoutputstream(); // create a PrinterWriter object for character-mode output PrintWriter Output = new PrintWriter(new OutputStreamWriter(outStream)); // write a message into the data stream Output.println(message); Acceptor //The ensuing flush method call is necessary for // the data to be written to the data //stream before the is closed. Output.flush(); connection accept /**/ System.out.println("message sent"); connect datasocket.close( ); /**/ System.out.println("data closed"); connectionsocket.close( ); data write /**/ System.out.println("connection closed"); message close catch (Exception ex) { ex.printstacktrace( ); //end catch close // end main // end class Requestor close connect request (from Socket constru read 22 public class Example4Requestor { if (args.length!= 2) System.out.println ("This program requires two command line arguments"); InetAddress acceptorhost = InetAddress.getByName(args[0]); int acceptorport = Integer.parseInt(args[1]); // instantiates a data Socket mysocket = new Socket(acceptorHost, acceptorport); /**/ System.out.println(" request granted"); // get an input stream for reading from the data InputStream instream = mysocket.getinputstream(); // create a BufferedReader object for text line input BufferedReader Input = new BufferedReader(new InputStreamReader(inStream)); /**/ System.out.println("waiting to read"); // read a line from the data stream String message = Input.readLine( ); Acceptor /**/ System.out.println("Message received:"); System.out.println("\t" + message); mysocket.close( ); /**/ System.out.println("data closed"); connection accept connect catch (Exception ex) { ex.printstacktrace( ); //end catch data write // end main message // end class close Requestor connect request (from Socket constructo read JAVA Stream Socket API (I) Java provee dos clases para s en modo stream: Server :para aceptar conexiones (conexion ) Socket: para intercambiar datos (Data ) for data exchange; we will call an object of this class a data. 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 on a specified port. Listens for a connection to be m ade to this and accepts it. T he m ethod blocks until a connection is m ade. C loses this. Set a tim eout period (in m illiseconds) so that a call to accept( ) for this w ill block for only this am ount of tim e. If the tim eout expires, a java.io.interruptedio E xception is raised close 23 Note: Accept is a blocking operation. 24 close

7 JAVA Stream Socket API (II) Metodos de Socket: Method/constructor Socket(InetAddress address, int port) void close() throws IOException InputStream getinputstream( ) throws IOException Creates a stream and connects it to the specified port number at the specified IP address Closes this. Returns an input stream so that data may be read from this. Protocolo HTTP OutputStream getoutputstream( )throws IOException void setsotimeout(int timeout) throws SocketException Returns an output stream so that data may be written to this. 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 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 s. 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

8 A sample HTTP session (telnet version) Web Client: Iexplorer, FireFox, Telnet,. 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 : close Content-Type: text/html <HTML> <HEAD> <TITLE> Mei-Ling L. Liu's Home Page </TITLE> </HEAD> <BODY bgcolor=#ffffff> 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 : close Content-Type: text/html <HTML> <HEAD> <TITLE> Mei-Ling L. Liu's Home Page </TITLE> </HEAD> <BODY bgcolor=#ffffff> 29 public class HTTPClient { if (args.length!= 3) System.out.println ("This program requires 3 command line arguments"); 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(" made"); mysocket.sendmessage(request); // 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(); catch (Exception ex) { System.out.println("ERROR : " + ex) ; ex.printstacktrace(system.out); // end catch // end else // end main //end class Send() GET filename HTTP/1.0\n\n response 1\r\n response2\r\n response3\n\n 30 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

9 Java URL Class Representa un Universal Resource Locator: protocolo dirección puerto camino +nombre fichero Method/Constructor URL(String spec) Creates a URL object from the URL name contained in a String URL(String protocol, String host, int port,string file) URL open() InputStream openstream() Creates a URL object from the specified protocol, host, port number, and file. Returns a URL 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: open().getinputstream() 33 public class URLBrowser { if (args.length!= 3) System.out.println ("This program requires 3 command line arguments"); 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 URL / HttpURL URL: Representa a connection to a URL. Method/Constructor 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. HttpURL Sub-clases de la anterior. Contiene métodos específicos para conexiones HTTP. Method/Constructor setrequestmethod(string method) 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