Windows process called by perl doesn't write to file properly

Question

I'm trying to call a perl script from another perl script, read from serial port, and write to a file. I've distilled my code to isolate the problem, so it probably won't make sense what the point of the code is.

Caller:

use Win32::Process;

my $perl_path = $^X;
my $SerialLogProcess;
my $SerialLogObj;
my $serial_log_script = "callee.pl";
Win32::Process::Create($SerialLogObj, "$perl_path", "perl $serial_log_script " ,0,NORMAL_PRIORITY_CLASS,".");
$SerialLogProcess = $SerialLogObj->GetProcessID();

print "waiting for 3 secs";
sleep(3);
print "done";
`taskkill /F /T /PID $SerialLogProcess`;

Callee:

use Win32::SerialPort;

my $portObj = new Win32::SerialPort("\\\\.\\COM70") || die; 
my $serialReading;
$portObj->baudrate(115200);
$portObj->parity("none");
$portObj->databits(8);
$portObj->stopbits(1);
system("rm -r \"log.txt\"");
open (LOGFILE, ">>log.txt") or die; 

while (1){
    $serialReading = $portObj->read(10);
    print LOGFILE $serialReading;
    #print LOGFILE " ";
}

So the caller creates a process for the callee script, and then kills it after 3 seconds. In those 3 seconds, I do something that gives guaranteed messages for the serial port to read. The log file is created, but nothing is written to it.

Heres what's weird: I can make the messages show up two ways. I run the callee script straight from the command line, or I can uncomment that last print. Unfortunately, these aren't solutions for me. I'm pretty stumped why I can't get my code to work properly, and it makes me think there is some kind of undefined behavior.

Answer 1

The output is buffered by default. The data will eventually be written once there's enough to write. Or you can use the following which will cause a flush for every print.

use IO::Handle qw( );   # Needed before Perl 5.14

open (LOGFILE, ">>log.txt") or die;
LOGFILE->autoflush(1);

But ug, why use a global variable???

open (my $LOGFILE, ">>log.txt") or die;
$LOGFILE->autoflush(1);
print $LOGFILE $serialReading;