void shutdown() {
        logThread.interrupt();
        try {
            logThread.executor.shutdownNow();
            logThread.executor.awaitTermination(600, TimeUnit.SECONDS);
            logThread.join();
        } catch (InterruptedException e) {
        }
    }
Flushes all queued messages, interrupts the log thread in this and
waits for it to end before returning
container-core/src/main/java/com/yahoo/container/logging/LogFileHandler.java