diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..eaf1da5
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+os/code/target/*
diff --git a/os/code/os/pom.xml b/os/code/os/pom.xml
new file mode 100644
index 0000000..6425d7c
--- /dev/null
+++ b/os/code/os/pom.xml
@@ -0,0 +1,81 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>com.scaler</groupId>
+  <artifactId>os</artifactId>
+  <version>pyenv shell 3.9.7</version>
+
+  <name>os</name>
+  <!-- FIXME change it to the project's website -->
+  <url>http://www.example.com</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>1.9</maven.compiler.source>
+    <maven.compiler.target>1.9</maven.compiler.target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.projectlombok</groupId>
+      <artifactId>lombok</artifactId>
+      <version>1.18.24</version>
+      <scope>provided</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
+      <plugins>
+        <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
+        <plugin>
+          <artifactId>maven-clean-plugin</artifactId>
+          <version>3.1.0</version>
+        </plugin>
+        <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
+        <plugin>
+          <artifactId>maven-resources-plugin</artifactId>
+          <version>3.0.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <version>3.8.0</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-surefire-plugin</artifactId>
+          <version>2.22.1</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-jar-plugin</artifactId>
+          <version>3.0.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-install-plugin</artifactId>
+          <version>2.5.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-deploy-plugin</artifactId>
+          <version>2.8.2</version>
+        </plugin>
+        <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
+        <plugin>
+          <artifactId>maven-site-plugin</artifactId>
+          <version>3.7.1</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-project-info-reports-plugin</artifactId>
+          <version>3.0.0</version>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
+</project>
diff --git a/os/code/os/src/main/java/com/scaler/App.java b/os/code/os/src/main/java/com/scaler/App.java
new file mode 100644
index 0000000..6a73e3c
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/App.java
@@ -0,0 +1,13 @@
+package com.scaler;
+
+/**
+ * Hello world!
+ *
+ */
+public class App 
+{
+    public static void main( String[] args )
+    {
+        System.out.println( "Hello World!" );
+    }
+}
diff --git a/os/code/os/src/main/java/com/scaler/addersubtractor/Adder.java b/os/code/os/src/main/java/com/scaler/addersubtractor/Adder.java
new file mode 100644
index 0000000..d42c8f2
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/addersubtractor/Adder.java
@@ -0,0 +1,22 @@
+package com.scaler.addersubtractor;
+
+import lombok.AllArgsConstructor;
+
+@AllArgsConstructor
+public class Adder implements Runnable {
+    private Count count;
+
+    @Override
+    public void run() {
+
+        for (int i = 1; i <= 100; ++i) {
+            count.getValue().getAndAdd(i);
+            try {
+                Thread.sleep(10);
+            } catch (Exception e) {
+                System.out.println("Something wrong happened");
+            }
+        }
+
+    }
+}
diff --git a/os/code/os/src/main/java/com/scaler/addersubtractor/Count.java b/os/code/os/src/main/java/com/scaler/addersubtractor/Count.java
new file mode 100644
index 0000000..348de30
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/addersubtractor/Count.java
@@ -0,0 +1,15 @@
+package com.scaler.addersubtractor;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class Count {
+    private AtomicInteger value = new AtomicInteger(0);
+
+    public AtomicInteger getValue() {
+        return value;
+    }
+
+    public void setValue(AtomicInteger value) {
+        this.value = value;
+    }
+}
diff --git a/os/code/os/src/main/java/com/scaler/addersubtractor/Runner.java b/os/code/os/src/main/java/com/scaler/addersubtractor/Runner.java
new file mode 100644
index 0000000..795718c
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/addersubtractor/Runner.java
@@ -0,0 +1,27 @@
+package com.scaler.addersubtractor;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+public class Runner {
+    public static void main(String[] args) {
+        Count count = new Count();
+
+        Adder adder = new Adder(count);
+        Subtractor subtractor = new Subtractor(count);
+
+        ExecutorService executor = Executors.newCachedThreadPool();
+        executor.execute(adder);
+        executor.execute(subtractor);
+
+        executor.shutdown();
+        try {
+            executor.awaitTermination(100, TimeUnit.SECONDS);
+        } catch (Exception e) {
+            System.out.println("Something wrong happened");
+        }
+
+        System.out.println(count.getValue());
+    }
+}
diff --git a/os/code/os/src/main/java/com/scaler/addersubtractor/Subtractor.java b/os/code/os/src/main/java/com/scaler/addersubtractor/Subtractor.java
new file mode 100644
index 0000000..ae80473
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/addersubtractor/Subtractor.java
@@ -0,0 +1,28 @@
+package com.scaler.addersubtractor;
+
+import java.util.concurrent.locks.Lock;
+
+import lombok.AllArgsConstructor;
+
+@AllArgsConstructor
+public class Subtractor implements Runnable {
+    private Count count;
+
+    @Override
+    public void run() {
+
+        for (int i = 1; i <= 100; ++i) {
+            count.getValue().getAndAdd(-i);
+            try {
+                Thread.sleep(10);
+            } catch (Exception e) {
+                System.out.println("Something wrong happened");
+            }
+
+            for (int j = 0; j < 10000; ++j) {
+                // do something
+            }
+        }
+
+    }
+}
\ No newline at end of file
diff --git a/os/code/os/src/main/java/com/scaler/producerconsumer/Consumer.java b/os/code/os/src/main/java/com/scaler/producerconsumer/Consumer.java
new file mode 100644
index 0000000..8fc0f05
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/producerconsumer/Consumer.java
@@ -0,0 +1,36 @@
+package com.scaler.producerconsumer;
+
+import java.util.Queue;
+import java.util.concurrent.Semaphore;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+
+@AllArgsConstructor
+@Getter
+public class Consumer implements Runnable {
+
+    private Queue<UnitOfWork> store;
+    private String name;
+    private Semaphore forProducer;
+    private Semaphore forConsumer;
+
+    @Override
+    public void run() {
+        while (true) {
+            try {
+                forConsumer.acquire();
+            } catch (InterruptedException e) {
+                throw new RuntimeException("Error acquiring semaphore " + e);
+            }
+
+            store.remove();
+            System.out.println("Consumed: " + name + " Left units :" + store.size());
+
+            forProducer.release();
+
+        }
+
+    }
+
+}
diff --git a/os/code/os/src/main/java/com/scaler/producerconsumer/Producer.java b/os/code/os/src/main/java/com/scaler/producerconsumer/Producer.java
new file mode 100644
index 0000000..d2650ec
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/producerconsumer/Producer.java
@@ -0,0 +1,36 @@
+package com.scaler.producerconsumer;
+
+import java.util.Queue;
+import java.util.concurrent.Semaphore;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+
+@AllArgsConstructor
+@Getter
+public class Producer implements Runnable {
+
+    private Queue<UnitOfWork> store;
+    private int maxSize;
+    private String name;
+    private Semaphore forProducer;
+    private Semaphore forConsumer;
+
+    @Override
+    public void run() {
+        while (true) {
+            try {
+                forProducer.acquire();
+            } catch (InterruptedException e) {
+                throw new RuntimeException("Error acquiring semaphore " + e);
+            }
+
+            store.add(new UnitOfWork());
+            System.out.println("Produced: " + name + " Left units :" + store.size());
+
+            forConsumer.release();
+        }
+
+    }
+
+}
diff --git a/os/code/os/src/main/java/com/scaler/producerconsumer/Runner.java b/os/code/os/src/main/java/com/scaler/producerconsumer/Runner.java
new file mode 100644
index 0000000..a9e5a81
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/producerconsumer/Runner.java
@@ -0,0 +1,35 @@
+package com.scaler.producerconsumer;
+
+import java.util.Queue;
+import java.util.Set;
+import java.util.concurrent.ConcurrentLinkedDeque;
+import java.util.concurrent.Semaphore;
+import java.util.stream.Collectors;
+
+public class Runner {
+
+    private static final Set<String> producerNames = Set.of("p1", "p2", "p3");
+    private static final Set<String> consumerNames = Set.of("c1", "c2", "c3", "c4");
+
+    public static void main(String[] args) {
+        Queue<UnitOfWork> store = new ConcurrentLinkedDeque<>();
+        int maxSize = 20;
+
+        Semaphore forProducer = new Semaphore(maxSize);
+        Semaphore forConsumer = new Semaphore(0);
+
+        Set<Producer> producers = producerNames
+                .stream()
+                .map(name -> new Producer(store, maxSize, name, forProducer, forConsumer))
+                .collect(Collectors.toSet());
+
+        Set<Consumer> consumers = consumerNames
+                .stream()
+                .map(name -> new Consumer(store, name, forProducer, forConsumer))
+                .collect(Collectors.toSet());
+
+        producers.forEach(producer -> new Thread(producer).start());
+        consumers.forEach(consumer -> new Thread(consumer).start());
+
+    }
+}
diff --git a/os/code/os/src/main/java/com/scaler/producerconsumer/UnitOfWork.java b/os/code/os/src/main/java/com/scaler/producerconsumer/UnitOfWork.java
new file mode 100644
index 0000000..484e681
--- /dev/null
+++ b/os/code/os/src/main/java/com/scaler/producerconsumer/UnitOfWork.java
@@ -0,0 +1,5 @@
+package com.scaler.producerconsumer;
+
+public class UnitOfWork {
+    
+}
diff --git a/os/code/os/src/test/java/com/scaler/AppTest.java b/os/code/os/src/test/java/com/scaler/AppTest.java
new file mode 100644
index 0000000..7ec3246
--- /dev/null
+++ b/os/code/os/src/test/java/com/scaler/AppTest.java
@@ -0,0 +1,20 @@
+package com.scaler;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/**
+ * Unit test for simple App.
+ */
+public class AppTest 
+{
+    /**
+     * Rigorous Test :-)
+     */
+    @Test
+    public void shouldAnswerWithTrue()
+    {
+        assertTrue( true );
+    }
+}
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