How does @Async work in Spring Boot and what are its limitations? स्प्रिंग बूट में @Async कैसे काम करता है और इसकी सीमाएँ क्या हैं?

@Async, enabled with @EnableAsync, runs an annotated method on a separate thread from a configured thread pool instead of the calling thread, letting the caller continue immediately without waiting for the method to finish — useful for fire-and-forget work like sending an email or logging an audit event.

Like @Transactional and @Cacheable, it works through a Spring proxy, so it has no effect on self-invoked calls within the same class. A void-returning async method silently swallows exceptions unless an AsyncUncaughtExceptionHandler is configured; a method that needs to report success/failure back to the caller should return CompletableFuture<T> instead of void.

@Async
public CompletableFuture<Void> sendWelcomeEmail(String email) {
    emailClient.send(email, "Welcome!");
    return CompletableFuture.completedFuture(null);
}