Nikola wrote:
Hi all,
i am writing small daemon.....and when i was seeing the end ......that
was just the beginning
of my problems.
General idea was to monitor list of files that was given on start.
For this example i am using test1.txt and test2.txt because I've
succeeded to replicate my problem
,at least i think so....:)))))
so the files are....
test1.txt
-----8<-----8<-----8<-----8<-----8<-----8<-----8<
Testing from test1
-----8<-----8<-----8<-----8<-----8<-----8<-----8<
test2.txt
-----8<-----8<-----8<-----8<-----8<-----8<-----8<
Testing from test1
-----8<-----8<-----8<-----8<-----8<-----8<-----8<
and daemon.c
Now the problem is following:
when i compile (gcc daemon.c => a.out) and run binary in this version
all works fine....and
if I do
#echo "some new line" >> test1.txt
i would see on my screen that select figured it out and i am having new
data for processing and it
would print it out.
but when i uncomment last fprintf my while and select goes
ballistic.....it prints numbers forever...not
blocking......
So why is that this line "fprintf(stderr,"%d\n",i++);" causes this
behavior.
tnx for help.
------------------------------------------------------------------------
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <stdio.h>
#include <stdlib.h>
int main(void) {
FILE *fp1,*fp2;
fd_set fdst;
char buffer[100];
int i;
if((fp1 = fopen("test1.txt","r")) == NULL){
return 0;
}
if((fp2 = fopen("test2.txt","r")) == NULL){
return 0;
}
/* Daemon-specific initialization goes here */
/* The Big Loop */
while (1) {
/* Do some task here ... */
FD_ZERO(&fdst);
FD_SET(fileno(fp1),&fdst);
FD_SET(fileno(fp2),&fdst);
select(fileno(fp2)+1,&fdst,NULL,NULL,NULL);
if(FD_ISSET(fileno(fp1),&fdst)){
while(fgets(buffer,100,fp1) != NULL){
puts(buffer);
}
}
if(FD_ISSET(fileno(fp2),&fdst)){
while(fgets(buffer,100,fp2) != NULL){
puts(buffer);
}
}
//fprintf(stderr,"%d\n",i++);
}
exit(EXIT_SUCCESS);
}
------------------------------------------------------------------------
1st: you can not use select on fd-s opened on regular files; use aio for
async. I/O;
2nd: leave the comment on. check the CPU - if I'm not mistaking, the
while(1){} goes nuts with or without fprintf();
M.D.
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