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Old 09-04-2004, 12:46 AM   #1
brunnopessoa
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Registered: Nov 2003
Location: Rio de Janeiro, Brazil
Distribution: Fedora
Posts: 67

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IPC Memory Share - C Program - Why not exiting for(;;) ??


Hi all!

I have two C program sources: PROC1.C and PROC2.C. Both share the same memory region, defined by t_info struct.

I only would like to know why it does NOT leave the FOR's when I type "sair" in the command line.

To run the program, you need pthread library and start first PROC1.C.

Tks a lot!
BP


/********* PROC1.C ********/


#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/errno.h>
#include <pthread.h>

typedef struct
{
int ok1, ok2;
char texto1[128], texto2[128];
}t_info;

extern int errno;
char *pgname;
t_info *info;

void * thread_escreve( void * arg ) {

for(;; ) {

printf("Digite um texto (proc1): ");

fgets( info->texto1, 128, stdin );
if( strcmp( info->texto1, "sair" ) == 0 ) {
info->ok1 = -1;
break;
} else {
info->ok1 = 1 ;
}
}
}


int main (int argc, char *argv[])
{
int md;
pthread_t tid;

pgname = argv[0];

// Criando a area de memoria compartilhada.
if ((md = shmget(8752, sizeof(t_info),0700|IPC_CREAT|IPC_EXCL)) == -1)
{
if (errno == EEXIST)
fprintf (stderr, "%s:Area de memoria ja existe.", pgname);
else
perror (pgname);
exit (-1);
}

// Mapeando a area de memoria compartilhada
if ((info = shmat (md, NULL, 0)) == (void *) -1)
{
perror (pgname);
exit (-1);
}

pthread_create( &tid, NULL, thread_escreve, NULL );

info->ok2 = 0;

for( ;; ) {

while (info->ok2 == 0)
/* aguarda */;
if( info->ok2 == -1 )
break;
printf ("Texto (proc1): %s", info->texto2);
info->ok2 = 0;
}

pthread_join( tid, NULL );

// Desfazendo o mapeamento
if (shmdt ((char *) info) == -1)
{
perror (pgname);
exit (-1);
}

// Destruindo a area de memoria
if (shmctl (md, IPC_RMID, NULL) == -1)
{
perror (pgname);
exit (-1);
}
}



/*********** PROC2.C ***********/

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/errno.h>
#include <pthread.h>

typedef struct
{
int ok1, ok2;
char texto1[128], texto2[128];
}t_info;

extern int errno;
char *pgname;
t_info * info;

void * thread_escreve( void * argumento ) {
for( ;; ) {
printf( "Digite um texto (proc2): " );

fgets( info->texto2, 128, stdin );
if( strcmp( info->texto2, "sair" ) == 0 ) {
info->ok2 = -1 ;
break;
} else {
info->ok2 = 1 ;
}
}
}

int main (int argc, char *argv[])
{
int md;
pthread_t tid;

pgname = argv[0];

// Obtendo o identificador da area de memoria compartilhada.
if ((md = shmget(8752, sizeof(t_info),0700)) == -1)
{
perror (pgname);
exit (-1);
}

// Mapeando a area de memoria compartilhada
if ((info = shmat (md, NULL, 0)) == (void *) -1)
{
perror (pgname);
exit (-1);
}

info->ok1 = 0;

pthread_create( &tid, NULL, thread_escreve, NULL );


for( ;; ) {

while( info->ok1 == 0 ) ;

if( info->ok1 == -1 )
break;
printf( "Texto (proc2): %s", info->texto1 );
info->ok1 = 0 ;
}

pthread_join( tid, NULL );

// Desfazendo o mapeamento
if (shmdt ((char *) info) == -1)
{
perror (pgname);
exit (-1);
}
}

Last edited by brunnopessoa; 09-04-2004 at 12:50 AM.
 
Old 09-04-2004, 02:29 AM   #2
infamous41md
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Registered: Mar 2003
Posts: 804

Rep: Reputation: 30
probably b/c fgets() includes the newline in the buffer you read in, and thus the strcmp() will not be equal. use strncmp() or chomp the newline.
 
Old 09-05-2004, 01:41 AM   #3
brunnopessoa
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Registered: Nov 2003
Location: Rio de Janeiro, Brazil
Distribution: Fedora
Posts: 67

Original Poster
Rep: Reputation: 15
Could you give me a tip in C code, please?

Tks in advance!!!
 
Old 09-05-2004, 04:39 AM   #4
bruce ford
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Registered: Jul 2004
Location: Munich, Germany
Distribution: Sun Solaris 8, SuSE 9.0
Posts: 43

Rep: Reputation: 15
hi,

infamous41md is right! Change your 2 strcmps to
Code:
strcmp( info->texto1, "sair\n" )
and to
Code:
strcmp( info->texto2, "sair\n" )
and it works.

so long...
bruce

Last edited by bruce ford; 09-05-2004 at 04:40 AM.
 
Old 09-05-2004, 10:27 PM   #5
brunnopessoa
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Registered: Nov 2003
Location: Rio de Janeiro, Brazil
Distribution: Fedora
Posts: 67

Original Poster
Rep: Reputation: 15
Tks a lot, guys!
 
  


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