# TP 1 -- Théorie de la concurrence

###### tags `TD` `M1 S1` `concurrence`
[Sommaire](/bAJa0viuQp68XN74HxpVJA)
> [time= 22 sept 2020]

[TOC]

## Exercice 1
### Enoncé


### Réponse

import java.io.*;

class Ex1
{
    public static void write_num(String name)
    {
        try
        {
            Writer wr = new FileWriter(name);
            DataOutputStream stream = new DataOutputStream(
                    new FileOutputStream(name));
            for (int k = 1; k < 100; k++)
            {
                int num = (int) (Math.random() * 50);
                wr.write(num + "\n");
            }
            wr.close();
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }
    public static void main(String[] args)
    {
        Ex1.write_num("file_ex1.txt");
    }
}

## Exercice 2
### Enoncé

### Réponse

public class Ex2
{
    static int count = 5;

    public static int average_sum(String path)
    {
        Result results = new Result(count);
        SommeThread[] threads = new SommeThread[count];
        for (int i = 0; i < count; i++)
        {
            threads[i] = new SommeThread(path, i, results);
            threads[i].start();
        }
        int res = 0;
        for (int i = 0; i < count; i++)
        {
            try
            {
                threads[i].join();
                int cur_sum = results.tab[i];
                System.out.printf("thread %d: %d\n",
                                  threads[i].id, cur_sum);
                res += cur_sum;

            } catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
        return res / count;
    }
    public static void main(String[] args)
    {
        String file_name = "file_ex1.txt";
        int result = Ex2.average_sum(file_name);
        System.out.println("result: " + result);
    }
}

public class Resultat
{
    public int[] tab;
    public Resultat(int size)
    {
        tab = new int[size];
    }
}

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;

public class SommeThread extends Thread
{
    public final String path;
    public final int id;
    Result result;

    public SommeThread(String path, int id, Result result)
    {
        this.path = path;
        this.id = id;
        this.result = result;
    }

    public void run()
    {
        try
        {
            FileReader file = new FileReader(new File(path));
            BufferedReader br = new BufferedReader(file);
            String line;
            int sum = 0;
            while ((line = br.readLine()) != null)
            {
                sum += Integer.parseInt(line);
            }
            result.tab[id] = sum;
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }
}

## Exercice 3
### Enoncé

### Réponse

#### 1)
Non

#### 2)
On peut récrire sur des valeurs.

#### 3)
on modifie la ligne `echange(a, b)` pour mettre
`synchonized(res){exchange(a, b)}`

## Exercice 4
### Enoncé

### Réponse
#### 1)
Non

#### 2)
On peut récrire sur des valeurs.

#### 3)
on ajoute un`synchronized` à la méthode `resultatbis.echange()`

## Exercice 5
### Enoncé

### Réponse