Here's the small C program to write to the FIFO I used:

#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>

int main(void)
{
        char buf[100];
        int fd = open("file.fifo", O_NONBLOCK|O_WRONLY);
        if (fd < 0) {
                fprintf(stderr, "error (%d): %s\n", errno, strerror(er
+rno));
                return 1;
        }

        sprintf(buf, "%s\n", "a new line");
        int bytes = write(fd, buf, strlen(buf) + 1);

        printf("wrote %d bytes", bytes);

        close(fd);
        return 0;
}
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Yes, that's exactly how i open the file. I should note that "text file buys" only happens after i open the pipe with my perl script and terminate it. After that, this error occurs irrespective of whether later i've got the script (reader) running together with the writer or a writer by itself.
To sum up, consider scenarios:

correct behavior:
1 echo "data" > file.fifo. Echo blocks on write, given that there's no reader running
2 start the script that opens a file.fifo and waits for data to come in
2.in a different terminal- echo "data" > file.fifo
3. Data is correctly received by the script
4.kill the script with Ctrl-C

Wrong behavior
After all of the above, perform the following:
a. script is not running. echo "data" > file.fifo results "text file busy".
b. start the script. The scripts open file.fifo for reading successfully.
c. echo "data" > file.fifo results "text file busy"
The script itself is quite big as it does some other processing but the actual code which operates the FIFO is very basic and pretty much boils down to (snippet):


my $alertsthr = threads->new(\&al_thread); 

$SIG{'INT'} = 'CLEANUP'; 
sub CLEANUP { 
    print "\nClosing pipe\n";    
    close PIPE; 
    exit(); 
}
 
sub al_thread 
{ 
  my $myline; 
  while (1) # keep reading from the pipe until we're killed 
  { 
      print "$config->{FIFO} open\n" if $config->{VERBOSE}; 
      open (PIPE, "$config->{FIFO}") or die "Could not open the input 
+pipe $config->{FIFO}\n"; 

      while($myline = <PIPE>) 
      { 
          print "read $myline\n" if $config->{VERBOSE}; 
          process_message($myline); 
      } 
      print "$config->{FIFO} EOF\n" if $config->{VERBOSE}; 
  } 
    
}
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