NTP Clock Flux

reactor-ntp-clock is a java.time.Clock implementation that uses NTP and a Reactor Flux to manage the current time. The included JMH benchmarks show about a 10-12% improvement in throughput over standard access of System.currentTimeMillis() via the system clock and more than a 1500% increase when using internal caching of the "now" value by setting a resolution to 1ms or more. This caching is important for situations where you're accessing the clock very many times within a matter of milliseconds but you only really need an "approximate" time of some configurable resolution.

The global static instance of the NTPClock has this caching disabled by default. Either set the system property to set a resolution value of 1ms or greater to affect the global clock, or create a new NTPClock using the CTOR.

Building

Build the project with Maven.

mvn clean install

Usage

A global Clock is available with a single threaded writer that updates the internal clock values and manages the NTP connection. Get access to this singleton and use it like any other Clock.

Instant now = NTPClock.getInstance().instant();
// Use the Instant API to manipulate the date

Configuring

Several system properties govern what NTP servers to use to keep time updated, what the default timeout is, and what the resolution in ms of the Clock is:

• -Dcom.jbrisbin.reactor.time.NTPClock.servers=0.pool.ntp.org,1.pool.ntp.org,2.pool.ntp.org,3.pool.ntp.org Comma-separated list of NTP servers to round-robin through.
• -Dcom.jbrisbin.reactor.time.NTPClock.timeout=30000 Default socket timeout value.
• -Dcom.jbrisbin.reactor.time.NTPClock.resolution=0 A value of 0 means disable caching internally. 1 or greater means cache the "now" value every resolution milliseconds and return that cached value instead of computing it each time.

Streaming Update Events

TimeInfo events are published into a Flux<TimeInfo> that is accessible via NTPClock.getTimeUpdates(). Subscribe to this Flux to get the raw TimeInfo objects that are created whenever an update is read from an NTP server.

NTPClock.getInstance().getTimeUpdates().subscribe(timeInfo -> {
  // handle TimeInfos
});

TODO Items

• Watch for errors in getting the NTP time and, if over a configurable amount, fall back to updating the now cache with currentTimeMillis.
• Record metrics for what servers are being hit and what the pool interval is, if it changes, and report them.
• Expose more of the internals to external management at runtime.

License

https://www.apache.org/licenses/LICENSE-2.0.html