Pawel Ciucias: Threading 07 Barrier

A Barrier is a synchronization primitive that enforces the stopping of execution between a number of threads or processes at a given point and prevents further execution until all threads or processors have reached the given point.

you can think of a barrier as a gate that all of your threads have to reach before moving forward. for example take a look at the following multi thread application.

using System;

using System.Threading;

namespace pc.threadBarrier

{

class Program

{

static Random rnd = new Random(DateTime.Now.Millisecond);

static void Main(string[] args)

{

var pawel = new Thread(CompleteTask);

pawel.Name = "Pawel";

var magda = new Thread(CompleteTask);

magda.Name = "Magda";

var tomek = new Thread(CompleteTask);

tomek.Name = "Tomek";

var jakub = new Thread(CompleteTask);

jakub.Name = "jakub";

var marin = new Thread(CompleteTask);

marin.Name = "Marin";

var threads = new Thread[] { pawel, magda, tomek, jakub, marin };

for (int i = 0; i < threads.Length; i++)

threads[i].Start(((char)(65+i)).ToString());

}

static void CompleteTask(object o)

{

var sleep = rnd.Next(1000, 2000);

var s1 = $"{Thread.CurrentThread.Name} is sleeping for {sleep * .001}'s";

Console.WriteLine(s1);

Thread.Sleep(sleep);

Thread.Sleep((int)Char.Parse(o.ToString()));

var s2 = $"{Thread.CurrentThread.Name} has completed {o.ToString()}";

Console.WriteLine(s2);

}

we start by creating five threads and passing them a task A to E, each letter has a higher ascii value 65 to 69, this is why after our threads sleep for a random number each one sleeps to the equivalent value of their task letter to ensure that they're printed in the ascending order. however because first each task sleeps for a random time between 1 and 2 seconds this is not possible, what we need is to sync all of our threads after their first sleep.

To sync our threads we use the barrier class.