in reply to Threads From Hell #3: Missing Some Basic Prerequisites [Solved]

You are queueing pixel by pixel. But the threads can calculate (x,y) by themselves. Why not do the following: 

my $width  = 1280 * 4;
my $height = 1024 * 4;

$picturesize = $width * $height;

for(my $i=0; $i< $picturesize-1; $i+=32){
        $start = $i;
        $end = $i+32;
        $x1 = int(($start % $width) /4);
        $y1 = int(($start / $width) /4);
        $x2 = int(($end % $width) /4);
        $y2 = int(($end / $width) /4);
        printf("(%4d,%4d)..(%4d,%4d) %d\n", 
                $x1,$y1,$x2,$y2, $i);
}

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This way, the main program only uses the picture size (a large integer), and increases it by 32 units (4 pixels with four byte RGBA perl pixel, I guess). And you give it a start and stop range: $i .. $i+32. The thread can then use those numbers to calculate back the pixels (x,y) themselves, in parallel.
startthread($from,$to,$width)

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Re^2: Threads From Hell #3: Missing Some Basic Prerequisites
by karlgoethebier (Abbot) on May 30, 2015 at 14:48 UTC

    Thank you very much for your reply FreeBeerReekingMonk.

    "...use those numbers to calculate back the pixels (x,y)..."

    The problem is that i don't understand these numbers:

    (   0,   0)..(   8,   0) 0
(   8,   0)..(  16,   0) 32
(  16,   0)..(  24,   0) 64
(  24,   0)..(  32,   0) 96
(  32,   0)..(  40,   0) 128
...

    [download]

    Ich stehe gerade auf dem Schlauch.

    Best regards, Karl

    «The Crux of the Biscuit is the Apostrophe»

[reply]
[d/l]

      Instead of enqueueing pixels, you enqueue an offset, and a length of 32 (and the thread will also need the width of the image).
      With that data, each thread is able to calculate itself its tasked pixels.

      Thus, if I have offset=0 the formula give calculates (x=0,y=0) to (x=8,y=0).
      If I have offset=32 the formula give calculates (x=8,y=0) to (x=16,y=0).

      Those are 8 pixels of 4 bytes each (RGBA).

      you can avoid that thread-save problem with imagemagick.
      You read an image and $blob=$original->ImageToBlob(); then manipulate all pixels in the blob, and BlobToImage() back.
      See this imagemagick post.
      And also this Permonk post: Re: reading in raw data into perl's ImageMagick

      At least these primitives are ok with threads? (although not your eyes, you see I used seizure inducing red and green lines... sorry for that)

      #! perl
use warnings;
use strict;
use threads;
use Image::Magick;

my $image = Image::Magick->new(
  size => "600x600",
);

$image->Read("xc:white");
for my $i (200..400){
  async{
    my $color = $i % 2 ? '#f00' : '#0f0';
    $image->Draw(
      primitive => 'line',
      points    => "$i,100 $i,500",
      stroke    => $color,
    );
  }->join;
}

$image->Set(magick=>'gif');                                           

my $blob = $image->ImageToBlob();

open(FH,"> $0.gif")or die "$!\n";
print FH $blob;
close FH;

      [download]

      perldoc threads

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[d/l]
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        Blue rectangle over striped pattern (writing to same pixels), threaded. The Rectangle does not survive intact...

        #! perl
use warnings;
use strict;
use threads;
use Image::Magick;

my $image = Image::Magick->new(
  size => "600x600",
);

$image->Read("xc:white");
for my $i (200..400){
  async{
    my $color = $i % 2 ? '#f00' : '#0f0';
    $image->Draw(
      primitive => 'line',
      points    => "$i,100 $i,500",
      stroke    => $color,
    );
  }->join;
  async{
    my $y = 100 + $i;
    $image->Draw(
      primitive => 'line',
      points    => "200,$y 400,$y",
      stroke    => '#00f'
    );
  }->join;
}

$image->Set(magick=>'gif');                                           

my $blob = $image->ImageToBlob();

open(FH,"> $0.gif")or die "$!\n";
print FH $blob;
close FH;

        [download]

        The example in the previous post with and without threading:

                       Rate     threaded non-threaded
threaded     1.41/s           --         -94%
non-threaded 24.7/s        1652%           --

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[d/l]
[select]

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