Thread synchronization in Perl and Python.

thread-sync.md

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In this post, we are talking about Thread Synchronization.

First in Perl:

[Source Code]

#!/usr/bin/env perl

use v5.38;
use threads;
use threads::shared;
use Thread::Semaphore;

my $semaphore = Thread::Semaphore->new(1);
my $resource :shared = 0;

sub worker {
    my $id = shift;

    $semaphore->down();

    $resource++;
    say "In thread $id, shared resource=$resource";

    $semaphore->up();
}

threads->create(\&worker, $_)->join foreach 1..5;

say "Final value of shared resource=$resource";

Time to test the code:

$ perl thread-sync.pl
In thread 1, shared resource=1
In thread 2, shared resource=2
In thread 3, shared resource=3
In thread 4, shared resource=4
In thread 5, shared resource=5
Final value of shared resource=5

I got this suggestion (below) on social platform by Füsilier Breitlinger:

[Source Code]

#!/usr/bin/env perl

use v5.38;
use threads;
use threads::shared;

my $resource :shared = 0;

sub worker {
    my $id = shift;

    lock $resource;
    $resource++;
    say "In thread $id, shared resource=$resource";
}

threads->create(\&worker, $_)->join foreach 1..5;

say "Final value of shared resource=$resource";

I liked this, as it does the same job with less code.

Let's do the same in Python:

[Source Code]

#!/usr/bin/env python3

import threading

lock = threading.Lock()
resource = 0

def worker(id):
    global resource

    with lock:
        resource += 1
        print(f"In thread {id}, shared {resource=}")

threads = []
for i in range(1, 6):
    t = threading.Thread(target=worker, args=(i,))
    threads.append(t)
    t.start()

for t in threads:
    t.join()

print(f"Final value of shared {resource=}")

Run the code now:

$ python3 thread-sync.py
In thread 1, shared resource=1
In thread 2, shared resource=2
In thread 4, shared resource=3
In thread 3, shared resource=4
In thread 5, shared resource=5
Final value of shared resource=5

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