public static void process(ExecSession exec,
            ProcessTask task, int taskIndex,
            ProcessStateCallback callback) {
        if (!(exec instanceof ExecSessionInternal)) {
            throw new IllegalArgumentException(new ClassCastException());
        }
        final ExecSessionInternal execInternal = (ExecSessionInternal) exec;

        ExecutorsInternal.process(execInternal, task, taskIndex, callback);
    }
Utility class for handling an executor plugin.

<p>It is considered to be an internal class, not for plugins. To make it explicit, {@link ExecutorsInternal} replaces it.
embulk-core/src/main/java/org/embulk/spi/util/Executors.java