org.apache.rocketmq.shaded.io.opentelemetry.sdk.trace.AnchoredClock Maven / Gradle / Ivy
/*
* Copyright The OpenTelemetry Authors
* SPDX-License-Identifier: Apache-2.0
*/
package org.apache.rocketmq.shaded.io.opentelemetry.sdk.trace;
import org.apache.rocketmq.shaded.io.opentelemetry.sdk.common.Clock;
import javax.annotation.concurrent.Immutable;
/**
* A utility for returning wall times anchored to a given point in time. Wall time measurements will
* not be taken from the system, but instead are computed by adding {@linkplain System#nanoTime()
* monotonic time} to the anchor point.
*
* This is needed because Java has lower granularity for epoch times and tracing events are
* recorded more often. There is also a performance improvement in avoiding referencing the system's
* wall time where possible. Instead of computing a true wall time for every timestamp within a
* trace, we compute it once at the local root and then anchor all descendant span timestamps to
* this root's timestamp.
*/
@Immutable
final class AnchoredClock {
private final Clock clock;
private final long epochNanos;
private final long nanoTime;
private AnchoredClock(Clock clock, long epochNanos, long nanoTime) {
this.clock = clock;
this.epochNanos = epochNanos;
this.nanoTime = nanoTime;
}
/**
* Returns a {@code AnchoredClock}.
*
* @param clock the {@code Clock} to be used to read the current epoch time and nanoTime.
* @return a {@code MonotonicClock}.
*/
public static AnchoredClock create(Clock clock) {
return new AnchoredClock(clock, clock.now(), clock.nanoTime());
}
/**
* Returns the current epoch timestamp in nanos calculated using {@link System#nanoTime()} since
* the reference time read in the constructor. This time can be used for computing durations.
*
* @return the current epoch timestamp in nanos.
*/
long now() {
long deltaNanos = clock.nanoTime() - this.nanoTime;
return epochNanos + deltaNanos;
}
/** Returns the start time in nanos of this {@link AnchoredClock}. */
long startTime() {
return epochNanos;
}
}