Hi All,
I have two programs, one writes to fifo (writefifo.c) and another reads from
fifo (readfifo.c) - sources at bottom of the mail).
The fifo has been created as myfifo
vi...@myhost:~/prg> ls -l myfifo
prw-r--r-- 1 vikas users 0 Feb 26 04:09 myfifo
Host is a 64 bit SLES (Suse) 10.
When I run writefifo on one terminal & readfifo on another, readfifo shows
me messages like:
vi...@myhost:~/prg> ./readfifo
Inside main
fd of fifo=3:
read 300 bytes --->message number #0<---
read 300 bytes ---><---
read 300 bytes --->message number #3<---
read 300 bytes ---><---
read 300 bytes --->message number #6<---
read 300 bytes ---><---
read 300 bytes --->message number #9<---
…
…
…
read 300 bytes --->message number #111<---
read 300 bytes ---><---
read 300 bytes --->message number #114<---
read 300 bytes ---><---
read 300 bytes --->message number #117<---
read 300 bytes ---><---
read 300 bytes --->message number #120<---
read 300 bytes ---><---
read 0 bytes ---><---
This happens all the time & happens on Solaris 10 too.
If I enable the *sleep(1)* in writefifo.c, I see the messages (yes, with a 1
second delay):
vi...@myhost:~/prg> ./readfifo
Inside main
fd of fifo=3:
read 200 bytes --->message number #0<---
read 200 bytes --->message number #1<---
read 200 bytes --->message number #2<---
read 200 bytes --->message number #3<---
read 200 bytes --->message number #4<---
read 200 bytes --->message number #5<---
read 200 bytes --->message number #6<---
read 200 bytes --->message number #7<---
read 200 bytes --->message number #8<---
read 200 bytes --->message number #9<---
…
…
…
read 200 bytes --->message number #118<---
read 200 bytes --->message number #119<---
read 200 bytes --->message number #120<---
read 200 bytes --->message number #121<---
read 200 bytes --->message number #122<---
read 0 bytes ---><---
I understand this is a problem with synchronization.
I can’t wait for 1 second as in the real program (a huge application) 1
second doesn’t work & I have to put 3 seconds which woirks but translates to
15 seconds (because the same function is called many times).
Please comment & suggest a better alternative.
*writefifo.c*
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#define MYFIFO "myfifo"
int main()
{
int fd=0,num=0,i=0;
char buffer[250];
printf("In writefifo \n");
fd=open(MYFIFO,O_WRONLY);
printf("Inside main, opened fd=%d\n",fd);
memset(buffer,'\0',250);
while (num<123)
{
//*sleep(1);*
i=sprintf(buffer,"message number #%d",num);
buffer[i+1]='\0';
//printf("buffer (sent) --->%s<---\n",buffer);
write(fd,buffer,200) ;
num++;
}
return 0;
}
*readfifo.c*
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#define FIFO_NAME "myfifo"
int main()
{
char s[300];
int num, fd;
printf("Inside main \n");
fd = open(FIFO_NAME, O_RDONLY);
printf("fd of fifo=%d:\n",fd);
do {
num=read(fd,s,300);
s[num] = '\0';
printf("read %d bytes --->%s<---\n",num,s);
} while (num > 0);
return 0;
}
Thanks in anticipation.
Regards
Vikas
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