Introduction to Multithreading in Java
Multithreading in Java allows concurrent execution of multiple threads within the same process. It enhances performance by leveraging the capabilities of modern processors that support multitasking.
Introduction to Java Concurrency
- **What is Concurrency?**
- Simultaneous execution of multiple tasks.
- Essential for maximizing CPU utilization and application responsiveness.
Why Concurrency Matters in Java?
- Enables efficient utilization of multi-core processors.
- Improves responsiveness in applications with I/O operations.
Threads in Java
-Threads Basics
- Lightweight processes within a process.
- Managed by JVM and OS.
Creating Threads using different ways
// Extending Thread class
class MyThread extends Thread {
public void run() {
System.out.println("Thread running");
}
}
// Implementing Runnable interface
class MyRunnable implements Runnable {
public void run() {
}
}
// Creating and starting threads
Thread thread1 = new MyThread();
thread1.start();
Thread thread2 = new Thread(new MyRunnable());
thread2.start();
Thread States and Lifecycle
- **Thread States**
- New, Runnable, Blocked, Waiting, Timed Waiting, Terminated.
- **Thread Lifecycle**
- Creation, Running, Waiting/Blocked, Dead.
- **Example: Thread States**
Thread.State state = thread.getState();
System.out.println("Thread state: " + state);
Synchronization and Locks
- **Thread Synchronization**
- Ensures only one thread accesses shared resources at a time.
- Prevents data inconsistencies.
- **Using `synchronized` Keyword**
public synchronized void increment() {
count++;
}
**Locks in Java**
- `ReentrantLock`, `ReadWriteLock`, `Semaphore`.
Problems with Threads
**Thread Safety Issues**
- Race conditions, deadlock, livelock.
- **Mitigating Issues**
- Proper synchronization, thread-safe collections, atomic variables.
Introducing Executors Framework
- **Executors Framework Overview**
- Higher-level concurrency utilities.
- Manages thread lifecycle and simplifies thread creation.
- **Benefits of Executors**
- Thread pooling, task scheduling, resource management.
Executors Service
- **ExecutorService Interface**
- Manages the execution of Runnable and Callable tasks.
- **Creating ExecutorService**
ExecutorService executor = Executors.newFixedThreadPool(5);
```
- Submitting Tasks
executor.submit(() -> {
System.out.println("Task executed");
});
ExecutorService Example: Callable and Future
- Callable Interface
- Represents a task that returns a result and may throw an exception.
- Future Interface
- Represents the result of an asynchronous computation.
-
Example: Callable and Future
Callable<Integer> task = () -> {
Thread.sleep(2000);
return 42;
};
Future<Integer> future = executor.submit(task);
Integer result = future.get(); // Blocking until result is available
System.out.println("Result: " + result);
Thread Pools and Executors Types
-Thread Pooling
- Reuse threads to reduce overhead of thread creation.
-Types of Executors
- `newFixedThreadPool`, `newCachedThreadPool`, `newSingleThreadExecutor`, `newScheduledThreadPool`.
- **Example: Using ThreadPoolExecutor**
ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(2);
executor.execute(() -> System.out.println("Task executed"));
CompletableFuture
- **CompletableFuture Overview**
- Asynchronous programming with fluent API.
- Combines Futures with callbacks.
- **Example: CompletableFuture**
```java
CompletableFuture.supplyAsync(() -> {
return "Hello";
}).thenApply(result -> result + " World")
.thenAccept(System.out::println);
Best Practices and Considerations
**Best Practices for Concurrency**
- Use thread-safe collections.
- Minimize shared mutable state.
- Avoid unnecessary synchronization.
**Considerations**
- Monitor thread pools and resource usage.
- Handle exceptions properly in asynchronous tasks.
System.out.println("Runnable running");
Conclusion
- **Key Takeaways**
- Java concurrency enables efficient utilization of resources.
- Executors service simplifies management of threads and tasks.
- Future-proof applications with CompletableFuture and asynchronous programming.