Re^3: Stumped with select->can

It's best to use sysread, but you will have to figure out a way to detect line endings. Maybe after concating the sysread data into a temp buffer then pull off lines with a regex or split. Read perldoc -f sysread. It will read as much as it can in a non-blocking manner. This will try to read in 1024 byte chunks, but will read less if that is all that is there.

while(@ready = $sel->can_read)
{
  foreach my $fh(@ready)
  {
    my $line = "";
    my $buf = "";

#    while(read($fh, $buf, 1024))
 while( my $bytes_read = sysread( $fh, $buf, 1024 ) > 0 )  ) {
      print "$bytes_read\n";
   {
      $line .= $buf;
    }
  }
}
[download]

I'm not really a human, but I play one on earth.
Old Perl Programmer Haiku ................... flash japh

Comment on Re^3: Stumped with select->can_read (buffered) Download Code

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Re^4: Stumped with select->can_read (buffered) by w1r3d (Initiate) on Aug 03, 2012 at 21:07 UTC
I tried doing that, but it didn't seem to work. My guess is that because one particular $fh is very busy, the while loop never ends? This seems to work at the moment: `while(@ready = $sel->can_read) { foreach my $fh(@ready) { my $line = ""; sysread( $fh, $line, 1024 ); } }` [download] My concern now is whether 1024 is too small of a buffer that I could miss something (if that's possible), or missing a newline character because of the buffer size. Would it be horrible (performance wise) to read one byte at a time until I reach a newline character, thus forming a real $line? Thanks again! Pedro	[reply] [d/l]
Re^5: Stumped with select->can_read (buffered) by tye (Sage) on Aug 03, 2012 at 21:24 UTC
My concern now is whether 1024 is too small of a buffer that I could miss something (if that's possible) If there are more than 1024 bytes to be read, then the next call to can_read() will tell you about them. - tye	[reply]
Re^5: Stumped with select->can_read (buffered) by zentara (Cardinal) on Aug 04, 2012 at 08:00 UTC
Would it be horrible (performance wise) to read one byte at a time until I reach a newline character, thus forming a real $line? It's been done before. :-) It certainly is inefficient. What I would do, is sysread as big of chunks as you can, then concat everything into a temp buffer, then split the buffer on newlines into an @array. If the scalar @array is greater than 1, then you have a line. Return the last @array element to your $temp_buffer, and process the rest of the @array elements as lines. It's called a sliding buffer, and you can google for "perl sliding buffer" for examples. I'm not really a human, but I play one on earth. Old Perl Programmer Haiku ................... flash japh	[reply]
Re^6: Stumped with select->can_read (concat) by tye (Sage) on Aug 04, 2012 at 16:48 UTC
sysread as big of chunks as you can, then concat everything into a temp buffer sysread can read onto the end of the buffer, avoiding the need to copy the data again: `sysread( $fh, $buf, 16*1024, length($buf) );` [download] - tye	[reply] [d/l]