EC
TimeoutException
JavaERRORNotableConcurrency

Operation timed out before completing

Quick Answer

Always pass a timeout to Future.get() and handle TimeoutException explicitly — cancel the future if the timeout is exceeded.

What this means

Thrown by java.util.concurrent operations (Future.get, BlockingQueue.poll) when a blocking call exceeds the specified timeout without completing. A checked exception — it must be handled or declared.

Why it happens
  1. 1Future.get(timeout, unit) called and the task did not complete in time
  2. 2CompletableFuture.get() with a timeout on a slow asynchronous operation

Fix

Handle TimeoutException with cancellation

Handle TimeoutException with cancellation
Future<String> future = executor.submit(task);
try {
    String result = future.get(5, TimeUnit.SECONDS);
} catch (TimeoutException e) {
    future.cancel(true);  // interrupt the running task
    throw new ServiceUnavailableException("Task timed out after 5s");
} catch (ExecutionException e) {
    throw new RuntimeException(e.getCause());
}

Why this works

Cancelling the future after a timeout interrupts the underlying thread, preventing resource leaks from abandoned long-running tasks.

Code examples
CompletableFuture timeout (Java 9+)java
CompletableFuture.supplyAsync(this::slowOperation)
    .orTimeout(3, TimeUnit.SECONDS)
    .exceptionally(ex -> "fallback");
Sources
Official documentation ↗

Java SE Documentation

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