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MCE-Shared-1.893
River stage one • 2 direct dependents • 3 total dependents
/ MCE::Shared::Handle

NAME

MCE::Shared::Handle - Handle helper class

VERSION

This document describes MCE::Shared::Handle version 1.893

DESCRIPTION

A handle helper class for use as a standalone or managed by MCE::Shared.

SYNOPSIS


            

              
              
# non-shared or local construction for use by a single process
# shorter, mce_open is an alias for MCE::Shared::Handle::open
use MCE::Shared::Handle;
MCE::Shared::Handle->open( my $fh, "<", "bio.fasta" )
   or die "open error: $!";
MCE::Shared::Handle::open  my $fh, "<", "bio.fasta"
   or die "open error: $!";
mce_open my $fh, "<", "bio.fasta" or die "open error: $!";
# construction for sharing with other threads and processes
# shorter, mce_open is an alias for MCE::Shared::open
use MCE::Shared;
MCE::Shared->open( my $fh, "<", "bio.fasta" )
   or die "open error: $!";
MCE::Shared::open  my $fh, "<", "bio.fasta"
   or die "open error: $!";
mce_open my $fh, "<", "bio.fasta" or die "open error: $!";
# example, output is serialized, not garbled
use MCE::Hobo;
use MCE::Shared;
mce_open my $ofh, ">>", \*STDOUT  or die "open error: $!";
mce_open my $ifh, "<", "file.log" or die "open error: $!";
sub parallel {
   $/ = "\n"; # can set the input record separator
   while (my $line = <$ifh>) {
      printf {$ofh} "[%5d] %s", $., $line;
   }
}
MCE::Hobo->create( \&parallel ) for 1 .. 4;
$_->join() for MCE::Hobo->list();
# handle functions
my $bool = eof($ifh);
my $off  = tell($ifh);
my $fd   = fileno($ifh);
my $char = getc($ifh);
my $line = readline($ifh);
binmode $ifh;
seek $ifh, 10, 0;
read $ifh, my($buf), 80;
print  {$ofh} "foo\n";
printf {$ofh} "%s\n", "bar";
open $ofh, ">>", \*STDERR;
syswrite $ofh, "shared handle to STDERR\n";
close $ifh;
close $ofh;

API DOCUMENTATION

MCE::Shared::Handle->new ( )

Called by MCE::Shared for constructing a shared-handle object.

open ( filehandle, expr )

open ( filehandle, mode, expr )

open ( filehandle, mode, reference )

In version 1.007 and later, constructs a new object by opening the file whose filename is given by expr, and associates it with filehandle. When omitting error checking at the application level, MCE::Shared emits a message and stop if open fails.


            

              
              
# non-shared or local construction for use by a single process
use MCE::Shared::Handle;
MCE::Shared::Handle->open( my $fh, "<", "file.log" ) or die "$!";
MCE::Shared::Handle::open  my $fh, "<", "file.log"   or die "$!";
mce_open my $fh, "<", "file.log" or die "$!"; # ditto
# construction for sharing with other threads and processes
use MCE::Shared;
MCE::Shared->open( my $fh, "<", "file.log" ) or die "$!";
MCE::Shared::open  my $fh, "<", "file.log"   or die "$!";
mce_open my $fh, "<", "file.log" or die "$!"; # ditto

mce_open ( filehandle, expr )

mce_open ( filehandle, mode, expr )

mce_open ( filehandle, mode, reference )

Native Perl-like syntax to open a file for reading:


            

              
              
# mce_open is exported by MCE::Shared or MCE::Shared::Handle.
# It creates a shared file handle with MCE::Shared present
# or a non-shared handle otherwise.
mce_open my $fh, "< input.txt"     or die "open error: $!";
mce_open my $fh, "<", "input.txt"  or die "open error: $!";
mce_open my $fh, "<", \*STDIN      or die "open error: $!";

and for writing:


            

              
              
mce_open my $fh, "> output.txt"    or die "open error: $!";
mce_open my $fh, ">", "output.txt" or die "open error: $!";
mce_open my $fh, ">", \*STDOUT     or die "open error: $!";

CHUNK IO

Starting with MCE::Shared v1.007, chunk IO is possible for both non-shared and shared handles. Chunk IO is enabled by the trailing 'k' or 'm' for read size. Also, chunk IO supports the special "\n>"-like record separator. That anchors ">" at the start of the line. Workers receive record(s) beginning with ">" and ending with "\n".


            

              
              
# non-shared handle ---------------------------------------------
use MCE::Shared::Handle;
mce_open my $fh, '<', 'bio.fasta' or die "open error: $!";
# shared handle -------------------------------------------------
use MCE::Shared;
mce_open my $fh, '<', 'bio.fasta' or die "open error: $!";
# 'k' or 'm' indicates kibiBytes (KiB) or mebiBytes (MiB) respectively.
# Read continues reading until reaching the record separator or EOF.
# Optionally, one may specify the record separator.
$/ = "\n>";
while ( read($fh, my($buf), '2k') ) {
   print "# chunk number: $.\n";
   print "$buf\n";
}

$. contains the chunk_id above or the record_number below. readline($fh) or $fh may be used for reading a single record.


            

              
              
while ( my $buf = <$fh> ) {
   print "# record number: $.\n";
   print "$buf\n";
}

The following provides a parallel demonstration. Workers receive the next chunk from the shared-manager process where the actual read takes place. MCE::Shared also works with threads, forks, and likely other parallel modules.


            

              
              
use MCE::Hobo;       # (change to) use threads; (or) use forks;
use MCE::Shared;
use feature qw( say );
my $pattern  = 'something';
my $hugefile = 'somehuge.log';
my $result = MCE::Shared->array();
mce_open my $fh, "<", $hugefile or die "open error: $!";
sub task {
   # the trailing 'k' or 'm' for size enables chunk IO
   while ( read $fh, my( $slurp_chunk ), "640k" ) {
      my $chunk_id = $.;
      # process chunk only if a match is found; ie. fast scan
      # optionally, comment out the if statement and closing brace
      if ( $slurp_chunk =~ /$pattern/m ) {
         my @matches;
         while ( $slurp_chunk =~ /([^\n]+\n)/mg ) {
            my $line = $1; # save $1 to not lose the value
            push @matches, $line if ( $line =~ /$pattern/ );
         }
         $result->push( @matches ) if @matches;
      }
   }
}
MCE::Hobo->create('task') for 1 .. 4;
# do something else
MCE::Hobo->waitall();
say $result->len();

For comparison, the same thing using MCE::Flow. MCE workers read the file directly when given a plain path, so will have lesser overhead. However, the run time is similar if one were to pass a file handle instead to mce_flow_f.

The benefit of chunk IO is from lesser IPC for the shared-manager process (above). Likewise, for the mce-manager process (below).


            

              
              
use MCE::Flow;
use feature qw( say );
my $pattern  = 'something';
my $hugefile = 'somehuge.log';
my @result = mce_flow_f {
   max_workers => 4, chunk_size => '640k',
   use_slurpio => 1,
},
sub {
   my ( $mce, $slurp_ref, $chunk_id ) = @_;
   # process chunk only if a match is found; ie. fast scan
   # optionally, comment out the if statement and closing brace
   if ( $$slurp_ref =~ /$pattern/m ) {
      my @matches;
      while ( $$slurp_ref =~ /([^\n]+\n)/mg ) {
         my $line = $1; # save $1 to not lose the value
         push @matches, $line if ( $line =~ /$pattern/ );
      }
      MCE->gather( @matches ) if @matches;
   }
}, $hugefile;
say scalar( @result );

CREDITS

Implementation inspired by Tie::StdHandle.

LIMITATIONS

Perl must have IO::FDPass for constructing a shared condvar or queue while the shared-manager process is running. For platforms where IO::FDPass isn't possible, construct condvar and queue before other classes. On systems without IO::FDPass, the manager process is delayed until sharing other classes or started explicitly.


            

              
              
use MCE::Shared;
my $has_IO_FDPass = $INC{'IO/FDPass.pm'} ? 1 : 0;
my $cv  = MCE::Shared->condvar();
my $que = MCE::Shared->queue();
MCE::Shared->start() unless $has_IO_FDPass;

Regarding mce_open, IO::FDPass is needed for constructing a shared-handle from a non-shared handle not yet available inside the shared-manager process. The workaround is to have the non-shared handle made before the shared-manager is started. Passing a file by reference is fine for the three STD* handles.


            

              
              
# The shared-manager knows of \*STDIN, \*STDOUT, \*STDERR.
mce_open my $shared_in,  "<",  \*STDIN;   # ok
mce_open my $shared_out, ">>", \*STDOUT;  # ok
mce_open my $shared_err, ">>", \*STDERR;  # ok
mce_open my $shared_fh1, "<",  "/path/to/sequence.fasta";  # ok
mce_open my $shared_fh2, ">>", "/path/to/results.log";     # ok
mce_open my $shared_fh, ">>", \*NON_SHARED_FH;  # requires IO::FDPass

The IO::FDPass module is known to work reliably on most platforms. Install 1.1 or later to rid of limitations described above.


            

              
              
perl -MIO::FDPass -le "print 'Cheers! Perl has IO::FDPass.'"

INDEX

MCE, MCE::Hobo, MCE::Shared

AUTHOR

Mario E. Roy, <marioeroy AT gmail DOT com>