Thread Pools and Executors

Thread pools and executors provide a way to manage and reuse threads in concurrent programming in Java. In this chapter, we will discuss the use cases of thread pools and executors and how to use them in Java, including complete code examples.

Use Cases of Thread Pools and Executors

Thread pools and executors are used in scenarios where creating and destroying threads frequently can be expensive. By reusing threads, we can improve performance and reduce resource usage. Some common use cases for thread pools and executors include:

Handling multiple client connections in a server
Performing batch processing of large amounts of data
Implementing parallel algorithms

Executor Interface

The Executor interface defines a simple API for executing tasks asynchronously in a separate thread.

Here's an example of using the Executor interface to execute a simple task.

Main


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import java.util.concurrent.Executor;
import java.util.concurrent.Executors;


class MyTask implements Runnable {
    public void run() {
        System.out.println("Hello, world!");
    }
}


public class ExecutorExample {
    public static void main(String[] args) {
        Executor executor = Executors.newSingleThreadExecutor();
        executor.execute(new MyTask());
    }
}

In this example, we create a MyTask class that implements the Runnable interface and prints "Hello, world!" when executed. We then create an executor using the Executors class and execute the MyTask instance using the execute method.

Thread Pools

Thread pools are a type of executor that manages a pool of threads, which can be reused to execute tasks. Here's an example of using a thread pool to execute multiple tasks.

Main


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import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;


class MyTask implements Runnable {
    private int taskId;

    public MyTask(int taskId) {
        this.taskId = taskId;
    }

    public void run() {
        System.out.println("Task " + taskId + " started.");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Task " + taskId + " finished.");
    }
}


public class ThreadPoolExample {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newFixedThreadPool(2);
        for (int i = 0; i < 4; i++) {
            executor.execute(new MyTask(i));
        }
        executor.shutdown();
    }
}

In this example, we create a MyTask class that takes an ID as a constructor parameter and sleeps for one second before printing a message indicating that the task is finished. We then create a thread pool with a fixed size of 2 using the Executors class and execute 4 instances of MyTask using the execute method. Finally, we shut down the thread pool using the shutdown method.

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Section 3. Chapter 4