20160820 Example For Multi Threading And Synchronized Data Structure Access

As mentioned in this blog post I have implemented a spike/test which shall show, that I am able to implement the Requirements For CISystem regarding multi threading and synchronized data structures holding the information about the nodes of the network.

My idea is to abstract from real node information (IP address, port number, name, …) and to use just a map instead, where the key (of the node) is just a character of the alphabet and the value is an Integer value, which is increased by 1 every time a thread adds its information to the map.

This is the description of what the classes/threads of my example do :

The class Threading owns the Map and creates the other threads
The Worker threads write an array of information (character strings) 10.000 times into the Map
The Reader thread reads 5 times the complete Map while it is filled by the Worker threads
The class Threading waits for all other threads to end to present the final state/content of the Map

This is the code of Threading.java

package com.wartbar.example;

import java.util.Map;
import java.util.HashMap;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;

public class Threading {

  public static Map<String, Integer> synchronizedMap = null;
  public static List<Thread> threads = new ArrayList<Thread>();

  public static void initSynchronizedMap() {
    Map<String, Integer> unsynchronizedMap = new HashMap<String, Integer>();
    synchronizedMap = Collections.synchronizedMap(unsynchronizedMap);
  }

  public static void add(String item) {
    synchronized(synchronizedMap) {
      Integer value = 1;
      if (synchronizedMap.containsKey(item)) {
        value = synchronizedMap.get(item);
        value++;
      }
      synchronizedMap.put(item,value);
    }
  }

  public Threading() {
    initSynchronizedMap();

    String[] info = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n"};

    for (int i=0; i<50; i++) {
      Thread t = new Thread(new Worker(info));
      t.start();
      threads.add(t);
    }

    Thread reader = new Thread(new Reader());
    reader.start();
    threads.add(reader);

    try {
      for (Thread t : threads) {
        t.join();
      }
    } catch (Exception e) {
      System.out.println(e);
    }

    synchronized(synchronizedMap) {
      System.out.println("Final state of the map: ");
      for (String item : synchronizedMap.keySet()) {
        System.out.println(item + ":" + synchronizedMap.get(item));
      }
    }
  }

}

This is the code of Worker.java

package com.wartbar.example;

public class Worker implements Runnable {

  private String myInfo[];

  public Worker(String[] info) {
    myInfo = info;
  }

  public void run() {
    try {
      for (int i=0; i<10000; i++) {
        for (String item : myInfo) {
          Threading.add(item);
        }
      }
    } catch (Exception e) {
      System.out.println(e);
    }
  }
}

This is the code of Reader.java

package com.wartbar.example;

public class Reader implements Runnable {

  public void run() {
    try {
      for (int i=0; i<5; i++) {
        synchronized(Threading.synchronizedMap) {
            System.out.println("Intermediate state of the map :");
            for (String item : Threading.synchronizedMap.keySet()) {
              System.out.println(item + ":" + Threading.synchronizedMap.get(item));
            }
        }
        Thread.sleep(1000);
      }
    } catch (Exception e) {
      System.out.println(e);
    }
  }
}

and this is the output when creating an object with new Threading()

Intermediate state of the map :
a:4338
b:4333
c:4330
d:4324
e:4323
f:4320
g:4316
h:4314
i:4313
j:4311
k:4308
l:4306
m:4306
n:4303
Intermediate state of the map :
a:112741
b:112736
c:112731
d:112726
e:112723
f:112720
g:112719
h:112715
i:112710
j:112707
k:112705
l:112703
m:112698
n:112696
Intermediate state of the map :
a:202609
b:202606
c:202599
d:202594
e:202591
f:202589
g:202587
h:202581
i:202579
j:202576
k:202573
l:202570
m:202569
n:202566
Intermediate state of the map :
a:292532
b:292525
c:292519
d:292508
e:292504
f:292503
g:292503
h:292502
i:292500
j:292499
k:292499
l:292498
m:292494
n:292491
Intermediate state of the map :
a:379525
b:379519
c:379518
d:379516
e:379513
f:379508
g:379506
h:379505
i:379504
j:379503
k:379500
l:379500
m:379499
n:379495
Final state of the map:
a:500000
b:500000
c:500000
d:500000
e:500000
f:500000
g:500000
h:500000
i:500000
j:500000
k:500000
l:500000
m:500000
n:500000