1 제 12 장 프로세스 사이의 통신. 2 Objectives describe how pipes are used for IPC define the two kinds of pipes use the system calls used with pipes network programming.

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제 12 장 프로세스 사이의 통신

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Objectives

describe how pipes are used for IPC

define the two kinds of pipes

use the system calls used with pipes

network programming with socket system call

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IPC using Pipes

IPC using regular files unrelated processes can share fixed size life-time lack of synchronization

IPC using pipes for transmitting data between related processes unidirectional communication can transmit an unlimited amount of data automatic synchronization on open()

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IPC using Pipes

data transmitting data is written into pipes using write() system

call data is read from a pipe using read() system

call automatic blocking when full or empty

types of pipes (unnamed) pipes named pipes

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Example

%who | sort

pipewho sort

write pointer ofanother process

read pointer of one process

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System Calls

int pipe(int fd[ ])

a process

fd[1] fd[0]

pipewriteread

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System Calls

전형적인 사용법1) a process creates a pipe2) fork child process3) the writer closes its read pipe descriptor, and

the reader closes its write pipe descriptor4) transmitting data via pipe using write() and read() system call5) each process closes its active pipe descriptor

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Pipe after fork

fd[1]Pipe

fd[0] fd[0]fd[1]

Parent Child

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Sending messages from child to parent

#include <stdio.h>#define READ 0#define WRITE 1char* phrase = “Stuff this in your pipe and smoke it”;main( ) {

int fd[2], bytesRead;char message[100];pipe(fd); if (fork() ==0) {

close(fd[READ]);write(fd[WRITE], phrase, strlen(phrase)+1);close(fd[WRITE]);

} else {

close(fd[WRITE]);bytesRead = read(fd[READ], message, 100);printf(“Read %d bytes: %s\n”, bytesRead,message);close(fd[READ]);

}}

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Example#include <stdio.h>#define READ 0#define WRITE 1main(argc, argv ) int argc; char* argv[];{

int fd[2];pipe(fd); if (fork() ==0) { close(fd[READ]); dup2(fd[WRITE],1); close(fd[WRITE]); execlp(argv[1], argv[1], NULL); perror(“Connect”); }

else {close(fd[WRITE]);dup2(fd[READ],0);close(fd[READ]);execlp(argv[2], argv[2], NULL);perror(“Connect”);

}}

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Named pipes

Why named pipes ? they have a name that exists in the file system they may be used by unrelated processes they exist until explicitly deleted

How to create named pipes ? by using the UNIX mknod commond with the p option

$mknod myPipe p$chmod ug+rw myPipe$ls -lg myPipe

by using the mknod() system call

int mknod(char* path, int mode, int dev)

return 0 if successful, -1 otherwise

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How to communicate via pipes ?

Writer process should open a named pipe for write-only write data using write() system call

Reader process should open a named pipe for read-only read data using read() system call

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Example:Reader

#include <stdio.h>#include <sys/types.h>#include <sys/stat.h>#include <sys/file.h>main( ) {

int fd;char str[100];unlink(“aPipe”);mknod(“aPipe”, S_IFIFO, 0);chmod(“aPipe”, 0660);fd = open(“aPipe”, O_RDONLY);

while (readLine(fd, str))printf(“%s\n”, str);

close(fd)}

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Example:Reader

readLine(fd, str)int fd; char *str;{ int n;

do {n = read(fd, str, 1);

} while (n>0 && *str++ != NULL);return (n>0);

}

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Example:Writer

#include <stdio.h>#include <sysfile.h>main( ) {

int fd, messageLen, i;char message[100];

sprintf(message, “Hello from PID %d”, getpid());messageLen= strlen(message)+1;do { fd = open(“aPipe”, O_WRONLY); if (fd == -1) sleep(1);} while(fd == -1);for (i =1; i<= 3; i++) {

write(fd, message, messageLen);sleep(3);

}close(fd);

}

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Sockets

Socket bidirectional connection process communication based on client-server model

AF_UNIX socket an interprocess communication mechanism between

processes on the same UNIX machine

AF_INET socket an interprocess communication mechanism between

processes across network

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The socket connection

Server

Server

Server

Client

Client

1. Sever creates a named socket

2. Client creates an unnamedsocket and request a connection

3. Server makes a connection.Server retains original named socket

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Client-Server Model

Server – Server creates a named socket

using socket()

– Server makes a pending queue using listen()

– Server accept() from a client connection()

– When a socket isconnected the server usually fork() a

child process to converse with the client

Client– Client creates an unnamed

socket using socket()

– Client requests a connection using connect()

– Client makes a connection when server accept( ) it.

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Creating a Socket

소켓 만들기 int socket(int domain, int type, int protocol)

domain AF_UNIX (the clients and server must be in the same machine) AF_INET(the and server may be anywhere on the Internet)

type SOCK_STREAM

protocol DEFAULT _PROTOCOL

ExampleserverFd = socket(AF_UNIX, SOCK_STREAM, DEFAULT _PROTOCOL);

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Naming a Socket

소켓에 이름 ( 주소 ) 주기 int bind(int fd, struct sockaddr* address, int

addressLen) bind the unnamed socket with fd to a name in address address is a pointer to

struct sockaddr_un sun_family = AF_UNIX sun_path = name of the socket

struct sockaddr_in sin_family = AF_INET sin_port = the port number of Internet socket sin_addr = 32-bit IP address

sin_zero = leave empty addressLen = length of address structure

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Example

serverUNIXAddress.sun_family = AF_UNIX;strcpy(serverUNIXAddress.sun_path, “recipe”);unlink(“recipe”);bind(serverFd, serverSockAddrPtr, serverLen);

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Creating a Socket Queue

소켓 큐 생성 specify the maximum number of pending

connections on a socket int listen(int fd, int queueLength) example

listen(serverFd, 5);

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Making the Connection

소켓에 연결 요청 int connect(int fd, struct sockaddr* address,

int addressLen) attempts to connect to a server socket whose

address is in a structure pointed to by address If successful, fd may be used to communicate with

the server’s socket

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Accepting a Client

소켓 연결 요청 수락 int accept(int fd, struct sockaddr* address, int*

addressLen)

(1) listen to the named server socket referenced by fd

(2) wait until a client connection request is received(3) creates an unnamed socket with the same attributes as the original server socket, and connects it to the client’s socket.(4) When a connection is made, address is set to the address of the client socket and addressLen is set to the actual size(5) return a new file descriptor

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Chef Server-Cook Client

%chef &

%cook

spam, spam, spam, spam,

spam, and spam

%cook

spam, spam, spam, spam,

spam, and spam

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Example : Chef Server(1/3)

#include <stdio.h>

#include <signal.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <sys/un.h>

#define DEFAULT_PROTOCOL 0

main ( ) {

int serverFd, clientFd, serverLen, clientLen;

struct sockaddr_un serverUNIXAddress;

struct sockaddr_un clientUNIXAddress;

struct sockaddr* serverSockAddrPtr;

struct sockaddr* clientSockAddrPtr;

signal(SIGCHLD, SIG_IGN);

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Example : Chef Server(2/3)

serverSockAddrPtr= (struct sockaddr*) &serverUNIXAddress;

serveLen = sizeof(serverUNIXAddress);clientSockAddrPtr = (struct sockaddr*)

&clientUNIXAddress;clientLen = sizeof(clientUNIXAddress);

serverFd = socket(AF_UNIX, SOCK_STREAM,DEFAULT_PROTOCOL);

serverUNIXAddress.sun_family = AF_UNIX;strcpy(serverUNIXAddress.sun_path, “receipe”);unlink(“receipe”);

bind(serverFd, serverSockAddrPtr, serverLen);listen(serverFd, 5);

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Example:Chef Server(3/3)

while (1) {clientFd = accept(serverFd, clientSockAddrPtr, &clientLen);if (fork ( ) == 0) {

writeRecipe(clientFd);close(clientFd);exit (0);

} else close(clientFd);}}writeRecipe(fd)int fd;{

static char* line1 =“spam, spam, spam, spam,”;static char* line2 = “spam and spam.”;write(fd, line1, strlen(line1)+1);write(fd, line2, strlen(line2)+1);

}

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Example:Cook Client(1/3)

#include <stdio.h>

#include <signal.h>



#include <sys/un.h>


main ( ) {

int clientFd, serverLen, result;

struct sockaddr_un serverUNIXAddress;


serverSockAddrPtr= (struct sockaddr*)

&serverUNIXAddress;

serverLen = sizeof(serverUNIXAddress);

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Example:Cook Client(2/3)

clientFd = socket(AF_UNIX, SOCK_STREAM, DEFAULT_PROTOCOL);

serverUNIXAddress.sun_family = AF_UNIX;

strcpy(serverUNIXAddress.sun_path, “receipe”);

do {result = connect(clientFd, serverSockAddrPtr, serverLen);

if (result == -1) sleep(1);

} while (result == -1);

readRecipe(clientFd);

close(clientFd);

exit(0) }

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Example:Client(3/3)

readRecipe(fd);int fd;{

char str[200];while (readLine(fd, str))

printf(“%s\n”, str);}readLine(fd, str)int fd;char* str;{

int n;do {

n = read(fd, str, 1);} while(n>0 && *str++ != NULL);return(n > 0);

}

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Internet Sockets

A client for Internet Time Listing Internet socket is specified by two values:

a 32-bit IP addressa 16-bit port number, which specifies a particular port

on the hostport number 13 is used to echo the host’s time

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Internet Sockets

A client for Internet Time Listing Internet socket address structure

struct sockaddr_insin_family = AF_INET sin_port = 16bit port number of the Internet

socketsin_addr = 32-bit IP address ,

which is a structure of type in_addr sin_zero = leave empty

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Example:Internet Time Listing

% inettime

Host name (q= quit, s= self): s

Self host name is cs

Internet Address= 203.252.195.1

The time on the target port is …

Host name (q= quit, s= self): monkey

Internet Address= 203.252.195.246


Host name (q= quit, s= self): 203.252.195.247


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Client:Internet Time Listing(1/4)

#include <stdio.h>

#include <signal.h>

#include <ctypes.h>



#include <netinet/in.h>

#include <arpa/inet.h>

#include <netdb.h>

#define DAYTIME_PORT 13


main ( ) {

int clientFd, serverLen, result;

struct sockaddr_in serverINETAddress;


unsigned long inetAddress;

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serverSockAddrPtr= (struct sockaddr*) &serverINETAddress;

serverLen = sizeof(serverINETAddress);

while (1) {

inetAddress = promptForINETAddress( );

if (inetAddress == 0)

break;

bzero((char*)&serverINETAddress,

sizeof(serverINETAddress));

serverINETAddress.sin_family = AF_INET;

serverINETAddress.sin_addr.s_addr = inetAddress;

serverINETAddress.sin_port = htons(DAYTIME_PORT);

clientFd = socket(AF_INET, SOCK_STREAM, DEFAULT_PROTOCOL);

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do { result = connect(clientFd, serverSockAddrPtr, serverLen); if (result == -1) sleep(1);} while (result == -1);readTime(clientFd);close(clientFd);}

exit(0);}

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readTime(fd)int fd;{ char str[200];

printf(“The time on the target port is”);while (readLine(fd, str))

printf(“%s\n”, str);}

readLine(fd, str)int fd; char* str;{ int n;

do {n = read(fd, str, 1);

} while (n > 0 && *str++ != ‘\n’);return(n > 0);

}

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promptForINETAddress

unsigned long promptForINETAddress(){

char hostName[100];unsigned long inetAddress;do {printf(“Host name (q=quit, s =self):”);

scanf(“%s”, hostName);if (strcmp(hostName, “q”) == 0) return(0);inetAddress = nameToAddr(hostName);if (inetAddress == 0)

printf(“Host name not found\n”);} while(inetAddress == 0);return(inetAddress);

}

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nameToAddr

unsigned long nameToAddr(name)char* name;{

char hostName[100];struct hostent* hostStruct;struct in_addr* hostNode;

if(isdigit(name[0])) return(inet_addr(name));if (strcmp(name, “s”) == 0) {

gethostname(hostName, 100); printf(“Self host name is %s\n”,hostName);} else strcpy(hostName, name);hostStruct = gethostbyname(hostName);if (hostStruct == NULL) return(0);hostNode = (struct in_addr*) hostStruct->h_addr;printf(“Internet Address = %s\n”,inet_ntoa(*hostNode));return(hostNode->s_addr);

}

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Miscellaneous system calls

unsigned long inet_addr(char* string) returns the 32-bit IP address that corresponds to the

A.B.C.D formt string

int gethostname(char* name, int nameLen) sets the character array name, of length nameLen to a

null-terminated string equal to the local host’s name

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Miscellaneous system calls

struct hostent* gethostbyname(char* name) searches the “/etc/hosts” file and returns a

pointer to a hostent structure that describes the file entry associated with the string name

char* inet_ntoa(struct in_addr address) returns a pointer to a string that describes

address in the format A.B.C.D.

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Internet Server(1/3)

#include <stdio.h>

#include <signal.h>



#include <netinet/in.h>

#include <arpa/inet.h>

#include <netdb.h>


main ( ) {

int serverFd, clientFd, serverLen, clientLen;

struct sockaddr_in serverINETAddress;

struct sockaddr_in clientINETAddress;


struct sockaddr* clientSockAddrPtr;

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int port = 13;

serverFd = socket(AF_INET, SOCK_STREAM, DEFAULT_PROTOCOL);

serverLen = sizeof(serverINETAddress);

bzero((char*) &serverINETAddress, serverLen);

ServerINETAddress.sin_family = AF_INET;

serverINETAddress.sin_addr.s_addr = htonl(INADDR_ANY);

serverINETAddress.sin_port = htons(port);

serverSockAddrPtr = (struct sockaddr*) &serverINETAddress;

bind(serverFd, serverSockAddrPtr, serverLen);

listen(serverFd, 5);

clientLen = sizeof(clientINETAddress);

clientSockAddrPtr = (struct sockaddr*) clientINETAddress

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while (1) {clientFd = accept(serverFd, clientSockAddrPtr, &clientLen);if (fork ( ) == 0) {

service(clientFd);close(clientFd);exit (0);

} else close(clientFd);}}

1 제 12 장 프로세스 사이의 통신. 2 Objectives describe how pipes are used for IPC define the two kinds of pipes use the system calls used with pipes network programming.

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