void maybeRegisterMetrics() {
            if (opened != null) {
                return;
            }

            opened = Counter.builder(idPrefix.name("connections"))
                            .tags(commonTags)
                            .tag(STATE, "opened")
                            .register(meterRegistry);
            if (numOpened > 0) {
                opened.increment(numOpened);
            }

            closed = Counter.builder(idPrefix.name("connections"))
                            .tags(commonTags)
                            .tag(STATE, "closed")
                            .register(meterRegistry);
            if (numClosed > 0) {
                closed.increment(numClosed);
            }

            active = Gauge.builder(idPrefix.name("active.connections"), this, Meters::activeConnections)
                          .tags(commonTags)
                          .register(meterRegistry);
        }
Creates a new instance with the specified {@link Meter} name.
core/src/main/java/com/linecorp/armeria/client/ConnectionPoolMetrics.java