A thread pool is a group of pre-instantiated reusable threads that are available to perform tasks. When a task is submitted, it is assigned to an idle thread in the pool. If all threads are busy, the task waits in a queue until a thread becomes available.
Thread pools offer several advantages:
When you submit a task to a thread pool, the following steps occur:
Thread pools are particularly useful in scenarios where you need to manage a large number of short-lived tasks, such as handling requests in a web server or processing a batch of jobs.
Java provides several built-in thread pool implementations in the java.util.concurrent package, with the most commonly used being ExecutorService. Let's explore how to create and use a thread pool in Java.
To create a thread pool in Java, you can use the Executors class, which provides various methods to create different types of thread pools.
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ThreadPoolExample {
public static void main(String[] args) {
// Create a fixed thread pool with 5 threads
ExecutorService executorService = Executors.newFixedThreadPool(5);
for (int i = 0; i < 10; i++) {
Runnable task = new Task(i);
executorService.execute(task);
}
executorService.shutdown();
}
}
class Task implements Runnable {
private int taskId;
public Task(int taskId) {
this.taskId = taskId;
}
@Override
public void run() {
System.out.println("Task " + taskId + " is being executed by " + Thread.currentThread().getName());
}
}
Java provides several types of thread pools, each designed for different scenarios:
Fixed Thread Pool : Creates a fixed number of threads. If all threads are busy, tasks are queued.
ExecutorService fixedPool = Executors.newFixedThreadPool(10);
Cached Thread Pool : Creates new threads as needed but reuses previously constructed threads when they are available. Suitable for executing many short-lived tasks.
ExecutorService cachedPool = Executors.newCachedThreadPool();
Single Thread Executor: Creates a single worker thread to execute tasks sequentially.
ExecutorService singlePool = Executors.newSingleThreadExecutor();
Scheduled Thread Pool: Creates a thread pool that can schedule commands to run after a given delay or periodically.
ScheduledExecutorService scheduledPool = Executors.newScheduledThreadPool(5);
In the example provided, a fixed thread pool with 5 threads is created. We submit 10 tasks to the pool. The pool assigns these tasks to the available threads. If all threads are busy, the tasks wait in the queue.
Expected Output:
Task 0 is being executed by pool-1-thread-1 Task 1 is being executed by pool-1-thread-2 Task 2 is being executed by pool-1-thread-3 Task 3 is being executed by pool-1-thread-4 Task 4 is being executed by pool-1-thread-5 Task 5 is being executed by pool-1-thread-1 Task 6 is being executed by pool-1-thread-2 Task 7 is being executed by pool-1-thread-3 Task 8 is being executed by pool-1-thread-4 Task 9 is being executed by pool-1-thread-5
Thread pools in Java offer a robust way to manage and execute tasks efficiently. By reusing a fixed set of threads, they reduce overhead and improve the performance of multi-threaded applications. Whether you're processing web requests, running background jobs, or executing parallel computations, thread pools are an essential tool in your Java concurrency toolkit.
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Read posts more at : Java Thread Pool: How to Efficiently Manage Threads
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