How to resolve the algorithm Atomic updates step by step in the C# programming language

Published on 12 May 2024 09:40 PM

How to resolve the algorithm Atomic updates step by step in the C# programming language

Table of Contents

Problem Statement

Define a data type consisting of a fixed number of 'buckets', each containing a nonnegative integer value, which supports operations to: In order to exercise this data type, create one set of buckets, and start three concurrent tasks:

The display task need not be explicit; use of e.g. a debugger or trace tool is acceptable provided it is simple to set up to provide the display. This task is intended as an exercise in atomic operations.   The sum of the bucket values must be preserved even if the two tasks attempt to perform transfers simultaneously, and a straightforward solution is to ensure that at any time, only one transfer is actually occurring — that the transfer operation is atomic.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Atomic updates step by step in the C# programming language

This code implements a thread-safe buckets data structure. The ThreadSafeBuckets class has an array of buckets, each of which is protected by a mutex, so that only one thread can access a bucket at a time. The class also has methods for getting the value of a bucket, transferring money from one bucket to another, and printing the contents of all the buckets.

The Program class creates a ThreadSafeBuckets object with 10 buckets, and then creates and starts two threads:

  1. The EqualizerThread randomly averages the values of two buckets.

  2. The RandomizerThread randomly redistributes the values between two buckets.

  3. The PrinterThread prints the contents of all the buckets every 50 milliseconds.

The output of the program will show the values of the buckets changing over time, as the two threads transfer money between them. The EqualizerThread will tend to make the values of the buckets more equal, while the RandomizerThread will tend to make the values more random.

Source code in the csharp programming language

using System; //Rand class
using System.Threading; //Thread, Mutex classes
public class ThreadSafeBuckets
{
    //This class is thread safe, and ensures that all operations on it are atomic.
    //Calling threads do not need to ensure safety.
    Random rand = new Random();
    int[] Buckets;
    object[] locks; //Mutexes for each bucket so they can lock individually
    public int BucketCount { get; private set; }
    public ThreadSafeBuckets(int bucketcount)
    {
        //Create buckets+mutexes and fill them with a random amount
        BucketCount = bucketcount;
        Buckets = new int[bucketcount];
        locks = new object[bucketcount];
        int startingtotal = 0;
        for (int i = 0; i < BucketCount; i++)
        {
            locks[i] = new object();
            Buckets[i] = rand.Next(30);
            startingtotal += Buckets[i];
        }
        //Print the starting total
        Console.WriteLine("Starting total: " + startingtotal);
    }
    public int GetBucketValue(int i)
    {
        return Buckets[i];
    }
    public void Transfer(int i, int j, int amount)
    {
        //Transfer amount from bucket i to bucket j
        if (i > BucketCount || j > BucketCount || i < 0 || j < 0 ||
            i == j || amount < 0)
            return;

        //To prevent deadlock, always lock the lower bucket first
        lock (locks[Math.Min(i, j)])
            lock (locks[Math.Max(i, j)])
            {
                //Make sure don't transfer out more than is in the bucket
                amount = Math.Min(amount, Buckets[i]);

                //Do the transfer
                Buckets[i] -= amount;
                Buckets[j] += amount;
            }
    }

    public void PrintBuckets()
    {
        int counter = 0;
        //Lock all the buckets in sequential order and print their contents
        for (int i = 0; i < BucketCount; i++)
        {
            Monitor.Enter(locks[i]);
            Console.Write(Buckets[i] + " ");
            counter += Buckets[i];
        }
        //Print the bucket total, then unlock all the mutexes
        Console.Write("= " + counter);
        Console.WriteLine();

        foreach (var l in locks)
            Monitor.Exit(l);
    }
}

class Program
{
    static ThreadSafeBuckets TSBs;

    public static void Main(){
        //Create the thread-safe bucket list
        TSBs = new ThreadSafeBuckets(10);
        TSBs.PrintBuckets();
        //Create and start the Equalizing Thread
        new Thread(new ThreadStart(EqualizerThread)).Start();
        Thread.Sleep(1);
        //Create and start the Randamizing Thread
        new Thread(new ThreadStart(RandomizerThread)).Start();
        //Use this thread to do the printing
        PrinterThread();
    }
    //EqualizerThread runs on it's own thread and randomly averages two buckets
    static void EqualizerThread()
    {
        Random rand = new Random();
        while (true)
        {
            //Pick two buckets
            int b1 = rand.Next(TSBs.BucketCount);
            int b2 = rand.Next(TSBs.BucketCount);
            //Get the difference
            int diff = TSBs.GetBucketValue(b1) - TSBs.GetBucketValue(b2);
            //Transfer to equalize
            if (diff < 0)
                TSBs.Transfer(b2, b1, -diff / 2);
            else
                TSBs.Transfer(b1, b2, diff/2);
        }
    }
    //RandomizerThread redistributes the values between two buckets
    static void RandomizerThread()
    {
        Random rand = new Random();
        while (true)
        {
            int b1 = rand.Next(TSBs.BucketCount);
            int b2 = rand.Next(TSBs.BucketCount);
            int diff = rand.Next(TSBs.GetBucketValue(b1));
            TSBs.Transfer(b1, b2, diff);
        }
    }
    //PrinterThread prints the current bucket contents
    static void PrinterThread()
    {
        while (true)
        {
            Thread.Sleep(50); //Only print every few milliseconds to let the other threads work
            TSBs.PrintBuckets();
        }
    }
}


  

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