void stopHealthChecker() {
        final int currentCount = requestCount.decrementAndGet();
        // Must be called after startHealthChecker, so it's always greater than or equal to 0.
        assert currentCount >= 0;
        if (currentCount != 0) {
            return;
        }

        final ScheduledHealthCheckerImpl current = impl.getAndSet(null);
        // Must be called after startHealthChecker, so it's always non null.
        assert current != null;

        current.stopHealthChecker(onHealthCheckerUpdate);
    }
This method must be called after the paired startHealthChecker completes to
guarantee the state consistency.
core/src/main/java/com/linecorp/armeria/server/healthcheck/ScheduledHealthChecker.java