I'm communicating between two non-related process (not folked from the same parent) using Named Pipe (fifo mode). The program works. However, the pile file seem to be limited
The OUTPUT of the writer:
Wrote to file. fd = 3
Wrote to file. fd = 3
...... other output ...
Wrote to file. fd = 3
Wrote to file. fd = 3
The OUTPUT of the reader is:
fd: 3. Received buffer: hello
fd: 4. Received buffer: hello
...... other output ...
fd: 1021. Received buffer: hello
fd: 1022. Received buffer: hello
fd: 1023. Received buffer: hello
MY PROBLEM: At fd
1023, the reader seems to STOP READING from file (there is no fd
1024, 1025, etc.). When it happens, the writer STOP WRITING (log "Wrote to file. fd = 3" stops display)
I try different msg
value ("hi", "where are you" ...), but the writer always stop at fd
1023
I really don't understand why. Could you explain for me? Thanks you so much!
Here is my code: The writer:
#include <stdio.h>
#include <stdlib.h> /* exit functions */
#include <unistd.h> /* read, write, pipe, _exit */
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>
int main()
{
int fd;
char * myfifo = "/tmp/myfifo";
char msg[] = "hello";
/* create the FIFO (named pipe) */
mkfifo(myfifo, 0666);
fd = open(myfifo, O_WRONLY);
if (fd < 0) {
return;
}
while(1) {
write(fd, msg, sizeof(msg));
printf("Wrote to file. fd = %d\n", fd);
sleep(1);
}
close(fd);
/* remove the FIFO */
unlink(myfifo);
return 0;
}
The reader:
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#define MAX_BUF 500
int main()
{
int fd;
char * myfifo = "/tmp/myfifo";
char buf[MAX_BUF];
while(1) {
/* open, read, and display the message from the FIFO */
fd = open(myfifo, O_RDONLY);
if (fd != -1) {
if (read(fd, buf, sizeof(buf)) > 0) {
printf("fd: %d. Received buffer: %s\n", fd, buf);
}
}
sleep(0.2);
}
close(fd);
return 0;
}
I really don't understand why. Could you explain for me?
There's a limit on the number of open file descriptors on your system. The limit can be checked in shell with ulimit -n
. It is configurable. See help ulimit
and man limits.conf
.
On your system the maximum number of open file descriptors seems to be at 1024 (on mine too!) Opening more will return -1
with errno=EMFILE
.
Your reader
program opens new file descriptors in a loop. After reaching the limit of open file descriptors, open
starts retuning -1
, which because of if (fd != -1) {
makes the program stop outputting anything.
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