ExecutorService là gì? Khác tạo thread thủ công thế nào?

ExecutorService (Java 5+) quản lý thread pool — bạn submit Runnable/Callable, executor lo phần còn lại.

new Thread() thủ công burst 10K request → 10K OS thread → OOM. Không reuse, không backpressure.

ExecutorService exec = Executors.newFixedThreadPool(10);
exec.execute(() -> handle(request));            // Runnable
Future<String> f = exec.submit(() -> fetch());  // Callable → Future<T>

exec.shutdown();
if (!exec.awaitTermination(30, TimeUnit.SECONDS)) exec.shutdownNow();

Factory trong Executors:

Sizing: CPU-bound = số core; I/O-bound truyền thống = cores × (1 + wait/compute); Java 21+ → Virtual Threads.

Sai lầm hay gặp: không shutdown (leak), newCachedThreadPool() không giới hạn (OOM), default queue unbounded, nuốt exception trong task không log.

Java 21+ pattern:

try (var exec = Executors.newVirtualThreadPerTaskExecutor()) {
  // auto-shutdown khi try kết thúc
}

Đừng new Thread() thủ công trong production.

Virtual Threads là chuẩn mới cho I/O workload.

ExecutorService (Java 5+) manages a thread pool — you submit Runnable/Callable, the executor handles the rest.

A manual new Thread() burst of 10K requests → 10K OS threads → OOM. No reuse, no backpressure.

ExecutorService exec = Executors.newFixedThreadPool(10);
exec.execute(() -> handle(request));            // Runnable
Future<String> f = exec.submit(() -> fetch());  // Callable → Future<T>

exec.shutdown();
if (!exec.awaitTermination(30, TimeUnit.SECONDS)) exec.shutdownNow();

Factories in Executors:

Sizing: CPU-bound = cores; traditional I/O-bound = cores × (1 + wait/compute); Java 21+ → Virtual Threads.

Common mistakes: forgetting to shut down (leak), unbounded newCachedThreadPool() (OOM), default unbounded queue, swallowing task exceptions without logging.

Java 21+ pattern:

try (var exec = Executors.newVirtualThreadPerTaskExecutor()) {
  // auto-shutdown when try block ends
}

Never call new Thread() directly in production.

Virtual Threads are the new standard for I/O workloads.