in reply to Re: missing values when using Parallel::ForkManager
in thread missing values when using Parallel::ForkManager

Thanks, Ken. I updated the source code, and hope this light version will explain my trouble. In fact, there was complaint from running the above code. It is "Use of uninitialized value $count". The code of this line is 
my $count = $result_buffer->{$id}->{$pwm};

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The missing value here indicates that this piece of code 
 my $count = count_pwm_num($pwm,$seq_1,$seq_2);

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did not perform its function when parameters were transferred here. $pwm is from list @ciona_pwm_array. Because after executing those lines, the result will catch either 1 or 0, 
if($count != 0) {
     $output_temp_handle->print($id);
     $output_temp_handle->print("\t$pwm\t1\n");
}
else {
     $output_temp_handle->print($id);
     $output_temp_handle->print("\t$pwm\t0\n");
}

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However, as shown in result table, several values were missed from certain rows, (row c missed value 1 in column B, row b missed value 1 in column A. The missing values have no specific pattern, and it seems randomly lost. I doubted for some reason it did not execute this code 
$pm->start and next PWM;

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But I do not know why. Thanks.

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Re^3: missing values when using Parallel::ForkManager
by Anonymous Monk on Jul 07, 2015 at 02:32 UTC
    I wrote a mini code for this problem which replicates my puzzle. 
    #!/usr/bin/perl

use strict;
use Parallel::ForkManager;

my $pm = Parallel::ForkManager->new(10);

foreach my $j (1..100) {
    LINKS:
    for my $i (1..10) {
        $pm->start and next LINKS;
        my $num = count($i);
        print $num,"\t";
        $pm->finish;
    }
    print "\n";
    $pm->wait_all_children;
}

sub count {
    my $num = shift;
    return $num + 1;
}

    [download]
    I expected each row should generate ten numbers from 2 to 11. However, several rows will miss values. Even worse, several rows output 11 numbers instead of 10 numbers, and have replicate, for example, 10 appear twice. Why?
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[d/l]

      I don't get any missed numbers; I always get 2..11. I moved the wait_all_children() line above the line that prints a newline so that the output is clearer and more consistent: 

      2       3       4       5       6       7       9       8       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       10      9       8     
+  11
2       3       4       5       6       7       9       10      11    
+  8
2       3       4       5       6       7       9       8       11    
+  10
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       9       11      8     
+  10
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       8       9       7       11    
+  10
2       3       4       5       6       7       9       10      8     
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       8       9       7       11    
+  10
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       8       9       10      7     
+  11
2       3       4       5       6       7       8       10      9     
+  11
2       3       4       5       6       7       9       10      8     
+  11
2       3       4       5       6       7       8       9       11    
+  10
2       3       4       5       6       7       9       10      8     
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       8       9       10    
+  11
2       3       4       5       6       7       9       10      8     
+  11

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      Doing things in parallel means that you can't guarantee in what order they will finish. Sometimes one process takes a bit longer than the others and so the numbers appear "out of order".

      - tye        

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[d/l]
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        You and Tye reminds me of the right solution to my problem.It seems that the FileHandle was not updated in child process. I therefore created a FileHandle in each child process instead of the parent process. Anyway, it is my own understanding. If someone know it, do drop me your message.
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