my $count     = 100_000;
my $num_calls = 4;

my $sum = 0;
sub inc { ++$sum for 1..$count; }

inc() for 1..$num_calls;
print("$sum\n");   # 400000

##</code><code>##

use threads;
use threads::shared;

my $count     = 100_000;
my $num_calls = 4;

my $sum : shared = 0;
sub inc { ++$sum for 1..$count; }

$_->join for map { threads->create( \&inc ) } 1..$num_calls;
print("$sum\n");   # 314813

##</code><code>##

+=======================+
|          CPU          |
+-----------+-----------+
| thread 1  | thread 2  |
+===========+===========+
| ...       |           |   T
| load $sum |           |   i
| inc       |           |   m
+-----------+-----------+   e
|           | ...       |   |
|           | load $sum |   |
|           | inc       |   v
|           | save $sum |
|           | ...       |
+-----------+-----------+
| save $sum |           |
| ...       |           |
+===========+===========+

##</code><code>##

use threads;
use threads::shared;

my $count     = 100_000;
my $num_calls = 4;

my $sum : shared = 0;
sub inc { for (1..$count) { lock($sum); ++$sum } }

$_->join for map { threads->create( \&inc ) } 1..$num_calls;
print("$sum\n");   # 400000

##</code><code>##

++s     sum = 233564 (expecting 400000)
s+=1    sum = 143915 (expecting 400000)
c.=l    length = 248149 (expecting 400000)
c=c.l   length = 123360 (expecting 400000)

##</code><code>##

use v5.8.0;

use strict;
use warnings;

use threads;
use threads::shared;


{
   my $count   = 100_000;
   my $threads = 4;

   my $sum : shared = 0;

   sub inc {
      for (1..$count) {
         ++$sum;
      }
   }

   $_->join
      for map { threads->create( \&inc ) }
          0..$threads-1;

   print("++s     sum = $sum (expecting " . ($count*$threads). ")\n");
}

{
   my $count   = 100_000;
   my $threads = 4;

   my $sum : shared = 0;

   sub inc_assign {
      for (1..$count) {
         $sum += 1;
      }
   }

   $_->join
      for map { threads->create( \&inc_assign ) }
          0..$threads-1;

   print("s+=1    sum = $sum (expecting " . ($count*$threads). ")\n");
}

{
   my $count   = 100_000;
   my $threads = 4;

   my $content : shared = '';

   sub append {
      my ($letter) = @_;
      for (1..$count) {
         $content .= $letter;
      }
   }

   $_->join
      for map { threads->create( \&append, chr(ord('a')+$_) ) }
          0..$threads-1;

   print("c.=l    length = " . length($content) .
         " (expecting " . ($count*$threads). ")\n");
}

{
   my $count   = 100_000;
   my $threads = 4;

   my $content : shared = '';

   sub concatenate {
      my ($letter) = @_;
      for (1..$count) {
         $content = $content . $letter;
      }
   }

   $_->join
      for map { threads->create( \&concatenate, chr(ord('a')+$_) ) }
          0..$threads-1;

   print("c=c.l   length = " . length($content) .
         " (expecting " . ($count*$threads). ")\n");
}