Unexpected sysread block

[Swarna]

When I execute test1.pl, test2.pl is blocking.

Any ideas as to why the sysread is not returning immediately.

Thanks
Swarna



########## test1.pl #########
#!perl

open (FD, "|-", "perl test2.pl");
sleep (100);


########### test2.pl ##########

#!perl

my $buffer;

while (1) {

print STDERR "before sysread \n";
$bytes = sysread(STDIN, $buffer, 524288) || last;
die "undef bytes \n" unless defined $bytes;
print STDERR "after sysread \n";

}
print STDERR "last statement\n";

 

[Ben Morrow]

Quoth (e-mail address removed) (Swarna):

When I execute test1.pl, test2.pl is blocking.

Any ideas as to why the sysread is not returning immediately.

########## test1.pl #########
#!perl

open (FD, "|-", "perl test2.pl");
sleep (100);


########### test2.pl ##########

#!perl

my $buffer;

while (1) {

print STDERR "before sysread \n";
$bytes = sysread(STDIN, $buffer, 524288) || last;
die "undef bytes \n" unless defined $bytes;
print STDERR "after sysread \n";

}
print STDERR "last statement\n";

Ummm... because you aren't sending it any data? sysread is
un-*buffered*, not non-*blocking*. If you want a non-blocking read
(which will return 0 immediately if there is no data in the pipe to
read) then you will need to do

use IO::Handle;

STDIN->blocking(0);

in test2.pl. This is more portable than setting non-blocking mode
yourself using fcntl.

Ben