in reply to Threads: How to share a FileHandle to Write

If you want to share a filehandle with all threads, there is no need to pass it to each thread individually. Just open it before you spawn your threads and they will inherit a cloned copy of it. Ie. This runs without errors: 

#!/opt/coolstack/bin/perl  -w
use strict;
use threads;
use threads::shared;
use FileHandle;

my $nthreads = 64;
my $x : shared; # For sync
my $fh = FileHandle->new("> out.txt");

my @thrs;

for(1..$nthreads){
  print "START $_ \n";
  my ($thr) =  threads->create(\&worker, $_);
  push @thrs ,$thr;
}
$_->join for @thrs;
print "STOP: " . localtime() . "\n";
$fh->close;
print `wc -l out.txt`;
exit;

#----------------------------------------------------
sub worker{
  my $id = shift;
  my $tmp;

  for(1..1000){
    lock $x;
    print $fh "bla blalbla bla blal bla bla bla bla\n" ; #NOT SHARED!!
+!!
  }
  print "$id>LOAD EXIT\n";
}

[download]

And produces:

c:\test>junk4
START 1
START 2
1>LOAD EXIT
START 3
2>LOAD EXIT
START 4
3>LOAD EXIT
...

START 60
59>LOAD EXIT
START 61
60>LOAD EXIT
START 62
61>LOAD EXIT
START 63
62>LOAD EXIT
START 64
63>LOAD EXIT
64>LOAD EXIT
STOP: Tue May 19 11:37:09 2009
  64000 out.txt

[download]
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

Replies are listed 'Best First'.
Re^2: Threads: How to share a FileHandle to Write
by gulden (Monk) on May 19, 2009 at 10:56 UTC
    The output result is wrong... Each FileHandle in each thread have its own context, we can't print to it concurrently. 
    -bash-3.00$ perl threads_file.pl
START 1
START 2
1>LOAD EXIT
START 3
START 4
START 5
START 6
2>LOAD EXIT
3>LOAD EXIT
...
59>LOAD EXIT
START 61
60>LOAD EXIT
START 62
61>LOAD EXIT
START 63
62>LOAD EXIT
START 64
63>LOAD EXIT
64>LOAD EXIT
STOP: Tue May 19 11:51:32 2009

    [download]
    63778 out.txt
[reply]
[d/l]

      It looks like your C-runtime libraries or Perl implementation is broken(1).

      I cannot reproduce your results on my platform:

      Read more... (3 kB)

      The only logical thing for CLONE to do for an open filehandle is dup() or dup2(), and according to the man pages for those calls: 

      NAME
       dup, dup2 - duplicate a file descriptor

SYNOPSIS
       #include <unistd.h>

       int dup(int oldfd);
       int dup2(int oldfd, int newfd);

DESCRIPTION
       dup and dup2 create a copy of the file descriptor oldfd.

       After successful return of dup or dup2, the old and new descrip
+tors may
       be used interchangeably.

      [download]
      They share locks, file position pointers and flags; for example, if the file position is modified by using lseek on one of the descriptors, the position is also changed for the other.
      
       The two descriptors do not share the close-on-exec flag, howeve
+r.

      [download]

      1. That is, your platform is exhibiting unspecified--thought clearly defined--behaviour.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
[select]
        I've tested in more than one SO, and the problem is the same. Try to increase the number of threads, in order to increase concurrency and you will get the same result.
[reply]

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