Reading and Writing to a Named Pipe - c

Question

I'm working with two programs. The customer.c program writes an int to a named pipe and the bank.c reads the pipe and prints the int. The customer will choose one of two named pipes, "atm1" and "atm2".
Ultimately I would like to run two customer.c programs, one for each pipe at the same time, but I have some issues with the writing and reading to the named pipe.
If I just run bank.c and one customer.c I don't get any output.
If I run bank.c and two customer.c the output doesn't always print or is out of order when it does.
I tried to use fsync() to flush but that didn't work either.
customer.c
int main(int argc, char *argv[]){
int fd, num =0;
if((fd = open(argv[1], O_WRONLY)) == -1){
...
}
while(1){
printf("Enter a integer:\n");
scanf("%d", &num);
if(num < 0){
break;
}
if(write(fd, &num, sizeof(num)) <= 0){...}
fsync(fd);
}
close(fd);
return 0;
}
bank.c
int main(){
int fd, sd, num=0, sret, fret, maxfd;
//fd_set readfds;
//struct timeval timeout;
if(mkfifo("atm1", 0666) == -1){...}
if(mkfifo("atm2", 0666) == -1){...}
if((fd = open("atm1", O_RDONLY)) == -1){...}
if((sd = open("atm2", O_RDONLY)) == -1){...}
while(1){
if((sret = read(sd, &num, sizeof(num))) > 0){
printf("%d\n", num);
}
if((fret = read(fd, &num, sizeof(num))) > 0){
printf("%d\n", num);
}
if(sret <= 0 && fret <= 0){
break;
}
}
close(fd);
close(sd);
return 0;
}
Any pointer?

Answer 1

you need to make multi-threads server for multiple same time recv. and require to check pipe name is already exist.
blank.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <pthread.h>
void *client(void *data)
{
char *pname = (char*) data ;
int sd =0 ;
int num ;
int sret=0 ;
if((sd = open(pname, O_RDONLY)) == -1) {
printf("open failed:%s\n", pname) ;
return NULL ;
}
printf("client[%d] start\n", sd) ;
while(1){
num=0 ;
if((sret = read(sd, &num, sizeof(num))) > 0){
printf("[%d] recv:%d\n", sd, num);
}
if(sret <= 0) {
break;
}
}
close(sd);
printf("client[%d] end\n", sd) ;
return NULL;
}
int main(){
int status ;
pthread_t t1, t2 ;
if(mkfifo("atm1", 0666) == -1) {
printf("mkfifio failed : %d\n", errno) ;
if (errno==EEXIST ) {
printf("already exist. ignore\n") ;
}
else
return -1;
}
if(mkfifo("atm2", 0666) == -1) {
printf("mkfifio failed2 : %d\n", errno) ;
if (errno==EEXIST ) {
printf("already exist. ignore\n") ;
}
else
return -1;
}
pthread_create(&t1, NULL, client, (void*)"atm1") ;
pthread_create(&t2, NULL, client, (void*)"atm2") ;
pthread_join(t1, (void**)&status) ;
pthread_join(t2, (void**)&status) ;
return 0;
}
you can access the atm1 and atm2 at the same time.
./customer atm1
./customer atm2