public Stopwatch stop() {
        long tick = ticker.read();
        Assert.isTrue(isRunning, "This stopwatch is already stopped.");
        isRunning = false;
        elapsedNanos += tick - startTick;
        return this;
    }
Stops the stopwatch. Future reads will return the fixed duration that had
elapsed up to this point.

@return this {@code Stopwatch} instance
@throws IllegalStateException if the stopwatch is already stopped.
lts-core/src/main/java/com/github/ltsopensource/core/commons/concurrent/limiter/Stopwatch.java