Mrta at 15:47, 9 April 2014

2014-04-09T15:47:21Z

TomOgn: Created page with "

http://www.cs.unibo.it/~renzo/so/pratiche/2005.02.10.pdf

Esercizio 1

/* Prova Pratica di Laboratorio di Sistemi Operativi 10 febb..."

2014-04-01T08:24:33Z

Created page with "<h1>http://www.cs.unibo.it/~renzo/so/pratiche/2005.02.10.pdf</h1> <h2>Esercizio 1</h2> <syntaxhighlight lang="C"> /* Prova Pratica di Laboratorio di Sistemi Operativi 10 febb..."

New page

<h1>http://www.cs.unibo.it/~renzo/so/pratiche/2005.02.10.pdf</h1>
<h2>Esercizio 1</h2>

<syntaxhighlight lang="C">
/*
Prova Pratica di Laboratorio di Sistemi Operativi
10 febbraio 2005
Esercizio 1

URL: http://www.cs.unibo.it/~renzo/so/pratiche/2005.02.10.pdf

Nota: variazione che prevede un gestore (Master), di un token ring
composto da n processi figli (Slaves).

@author: Tommaso Ognibene
*/

// Dependencies
#include <ctype.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

// Constants
#define True 1
#define False 0

// Data types
struct tokenRing
{
pid_t Pid;
int Token[2];
int Output[2];
struct tokenRing *Next, *Prev;
};

typedef struct tokenRing TokenRing;

// Function declarations
static inline void errorAndDie(const char *msg);
static inline void printAndDie(const char *msg);
static inline void testTokenRing(int n);
static inline int isNumber(char *text);

// Entry point
extern void run(int argc, char *argv[])
{
// Pre-conditions
if (argc != 2)
printAndDie("The function requires one parameter to be passed in.");
if (!isNumber(argv[1]))
printAndDie("The parameter should be a natural number.");

testTokenRing(atoi(argv[1]));
}

/*
* Check whether a string is a natural number or not
* Input: str, the string
* Output: 1, if the string is a natural number
* 0, else
*/
static inline int isNumber(char *str)
{
int i;

i = 0;
while (i < strlen(str) && isdigit(str[i]))
i++;

return i == strlen(str);
}

/*
* Create a token ring of n processes.
* The parent shall manage the token ring.
* Run a test showing the main logical steps in the parent standard output.
* Input: n, the number of processes
*/
static inline void testTokenRing(int n)
{
const char fifoPath[] = "token.fifo";
char token[5] = "token";
char buffer[512];
int i, fifo;
pid_t pid;
ssize_t count;
TokenRing *it, *first, *temp;

// First element of the token ring
first = it = (TokenRing *) malloc(sizeof (TokenRing));

// Create the named pipe if it does not yet exist
if (access(fifoPath, F_OK) < 0)
if (mkfifo(fifoPath, S_IRWXU) < 0)
errorAndDie("mkfifo");

for (i = 0; i < n; i++)
{
// Create a pipe for token communication
if (pipe(it->Token) < 0)
errorAndDie("pipe");

// Create a pipe for output redirection
if (pipe(it->Output) < 0)
errorAndDie("pipe");

// Fork
pid = fork();
if (pid < 0)
errorAndDie("fork");

// Child process
if (pid == 0)
{
// Open named pipe for writing
fifo = open(fifoPath, O_WRONLY);
if (fifo < 0)
errorAndDie("open");

// Close output side
if (close(it->Token[1]) < 0)
errorAndDie("close");

// Close input side
if (close(it->Output[0]) < 0)
errorAndDie("close");

// Re-direct the standard output
if (dup2(it->Output[1], STDOUT_FILENO) < 0)
errorAndDie("dup2");

while (True)
{
// Clear the buffer
memset(buffer, 0, sizeof (buffer));

// Wait for the token
count = read(it->Token[0], buffer, sizeof (buffer));
if (count < 0)
errorAndDie("read");

fprintf(stdout, "[slave #%d] Received the token from Master.\n", getpid());
fprintf(stdout, "[slave #%d] I'm gonna do some stuff now.\n", getpid());
fflush(stdout);
sleep(2);
fprintf(stdout, "[slave #%d] Giving back the token to Master.\n", getpid());
fflush(stdout);

// Give the token back
count = write(fifo, token, sizeof (token));
if (count < 0)
errorAndDie("write");
}

// Close the pipes
if (close(it->Token[0]) < 0 || close(it->Output[1]) < 0 || close(fifo) < 0)
errorAndDie("close");

exit(EXIT_SUCCESS);
}

// Close unused sides of the pipes
if (close(it->Token[0]) < 0 || close(it->Output[1]) < 0)
errorAndDie("close");

it->Pid = pid;

if (i + 1 == n)
break;

it->Next = (TokenRing *) malloc(sizeof (TokenRing));
temp = it;
it = it->Next;
it->Prev = temp;
}
it->Next = first;
first->Prev = it;

// Open named pipe for reading
fifo = open(fifoPath, O_RDONLY);
if (fifo < 0)
errorAndDie("open");

// Manage the token ring
it = first;
while (True)
{
// Clear the buffer
memset(buffer, 0, sizeof (buffer));

// Assign the token
printf("[Master] Assigning the token to slave #%d\n", it->Pid);
count = write(it->Token[1], token, sizeof (token));
if (count < 0)
errorAndDie("write");

// Redirect the children output
for (i = 0; i < 2; i++)
{
count = read(it->Output[0], buffer, sizeof (buffer));
if (count < 0)
errorAndDie("read");

if (write(STDOUT_FILENO, buffer, count) < 0)
errorAndDie("write");
}

// Wait for the token in return
count = read(fifo, buffer, sizeof (buffer));
if (count < 0)
errorAndDie("read");
printf("[Master] Received the token from slave #%d\n", it->Pid);

it = it->Next;
}

// Close the pipes
if (close(it->Token[1]) < 0 || close(it->Output[0]) < 0 || close(fifo) < 0)
errorAndDie("close");

// Remove the named pipe
if (unlink(fifoPath) < 0)
errorAndDie("unlink");
}

/*
* Print error message and exit
* Input: msg, the error message
*/
static inline void errorAndDie(const char *msg)
{
perror(msg);
exit(EXIT_FAILURE);
}

/*
* Print message and exit
* Input: msg, the message
*/
static inline void printAndDie(const char *msg)
{
printf("%s\n", msg);
exit(EXIT_FAILURE);
}
</syntaxhighlight>

@@ Line 1: / Line 1: @@
-<h1>http://www.cs.unibo.it/~renzo/so/pratiche/2005.02.10.pdf</h1>
+== Esercizio 1 ==
-<h2>Esercizio 1</h2>
 <syntaxhighlight lang="C">
@@ Line 247: / Line 257: @@
 	printf("%s\n", msg);
 	exit(EXIT_FAILURE);
+}
 </syntaxhighlight>

ProvaPratica 2005.02.10 - Revision history

Mrta at 15:47, 9 April 2014

TomOgn: Created page with "

http://www.cs.unibo.it/~renzo/so/pratiche/2005.02.10.pdf

Esercizio 1