[D-H-O-R-A]

Summary of Changes

Fixes #3480

Problem Description

As reported in #3480, nodes frequently log warnings from kamon.metric.Timer during block application or mining:

WARN  [ecution-context-global-XX] kamon.metric.Timer - Failed to record value [-70000000] on [span.processing-time,{operation=block-appender,error=false}] because the value is outside of the configured range. The recorded value was adjusted to the highest trackable value [3600000000000].

Root Cause

1. In com.wavesplatform.metrics.TimerExt, startedTimer.stop() uses Kamon's clock, which relies on the system wall-clock time. When NTP synchronizes or shifts the system clock backwards during block execution, the calculated duration is negative.
2. Kamon's histogram rejects negative values with an out-of-range warning and falls back to recording 3,600,000,000,000ns.
3. Furthermore, timer allocations and measurements executed unconditionally even when metrics were disabled in user configuration.

Solution

1. Monotonic Clock: Use System.nanoTime() (which uses CLOCK_MONOTONIC on Linux), guaranteeing that time never moves backwards even during NTP time synchronization.
2. Non-positive duration guard: Ensure that only strictly positive durations (elapsed > 0) are recorded into Kamon metrics.
3. Bypass on disabled metrics: Check Kamon.enabled() before measuring to execute f directly with zero allocations and zero CPU overhead when metrics are disabled.
4. Unit Tests: Added TimerExtSpec verifying measure, measureSuccessful, and measureOptional behavior.