synchronized(this) {
  taskMap.compute(lambda);
}

public class ThreadPoolExecutor extends AbstractExecutorService {
 ...
 /**
     * Initiates an orderly shutdown in which previously submitted
     * tasks are executed, but no new tasks will be accepted.
     * Invocation has no additional effect if already shut down.
     *
     * <p>This method does not wait for previously submitted tasks to
     * complete execution.  Use {@link #awaitTermination awaitTermination}
     * to do that.
     *
     * @throws SecurityException {@inheritDoc}
     */
    public void shutdown() {

synchronized(this) {
  taskMap.compute(lambda);
}

        CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
            System.out.println("Task with exception");
            throw new RuntimeException();
        });
        Thread.sleep(100);

        future.whenCompleteAsync((r, e) -> System.out.println("Main thread"));

    public static void main(String[] args) throws InterruptedException {
        CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Task with exception");
            throw new RuntimeException();
        });
        Thread.sleep(100);

        future.whenCompleteAsync((r, e) -> System.out.println("Main thread"));
        Thread.sleep(2000);