Szymański's algorithm
# 20230822 Raku programming solution
use OO::Monitors;
my \N = 10;
monitor Szymański {
has @.tasks;
my $critical = 0;
method runSzymański($id) {
@.tasks[$id] = 1;
( my @others = @.tasks ).splice: $id,1;
until @others.all ~~ 0|1|2 { $*THREAD.yield }
@.tasks[$id] = 3;
if @others.any ~~ 1 {
@.tasks[$id] = 2;
until @others.any ~~ 4 { $*THREAD.yield }
}
@.tasks[$id] = 4;
until @.tasks[^$id].all ~~ 0|1 { $*THREAD.yield }
$critical = ((my $previous = $critical) + $id * 3) div 2;
say "Thread $id changed the critical value from $previous to $critical";
until @.tasks[$id^..*-1].all ~~ 0|1|4 { $*THREAD.yield }
@.tasks[$id] = 0
}
}
my $flag = Szymański.new: tasks => 0 xx N;
await Promise.allof( ^N .pick(*).map: { start { $flag.runSzymański: $_ } } );
Output:
Thread 6 changed the critical value from 0 to 9
Thread 1 changed the critical value from 9 to 6
Thread 5 changed the critical value from 6 to 10
Thread 4 changed the critical value from 10 to 11
Thread 7 changed the critical value from 11 to 16
Thread 9 changed the critical value from 16 to 21
Thread 8 changed the critical value from 21 to 22
Thread 3 changed the critical value from 22 to 15
Thread 2 changed the critical value from 15 to 10
Thread 0 changed the critical value from 10 to 5
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