Method Collect

prometheus/go_collector_latest.go:306–370

Collect returns the current state of all metrics of the collector.

(ch chan<- Metric)

// Collect returns the current state of all metrics of the collector.
func (c *goCollector) Collect(ch chan<- Metric) {
	// Collect base non-memory metrics.
	c.base.Collect(ch)

	if len(c.sampleBuf) == 0 {
		return
	}

	// Collect must be thread-safe, so prevent concurrent use of
	// sampleBuf elements. Just read into sampleBuf but write all the data
	// we get into our Metrics or MemStats.
	//
	// This lock also ensures that the Metrics we send out are all from
	// the same updates, ensuring their mutual consistency insofar as
	// is guaranteed by the runtime/metrics package.
	//
	// N.B. This locking is heavy-handed, but Collect is expected to be called
	// relatively infrequently. Also the core operation here, metrics.Read,
	// is fast (O(tens of microseconds)) so contention should certainly be
	// low, though channel operations and any allocations may add to that.
	c.mu.Lock()
	defer c.mu.Unlock()

	// Populate runtime/metrics sample buffer.
	metrics.Read(c.sampleBuf)

	// Collect all our runtime/metrics user chose to expose from sampleBuf (if any).
	for i, metric := range c.rmExposedMetrics {
		// We created samples for exposed metrics first in order, so indexes match.
		sample := c.sampleBuf[i]

		// N.B. switch on concrete type because it's significantly more efficient
		// than checking for the Counter and Gauge interface implementations. In
		// this case, we control all the types here.
		switch m := metric.(type) {
		case *counter:
			// Guard against decreases. This should never happen, but a failure
			// to do so will result in a panic, which is a harsh consequence for
			// a metrics collection bug.
			v0, v1 := m.get(), unwrapScalarRMValue(sample.Value)
			if v1 > v0 {
				m.Add(unwrapScalarRMValue(sample.Value) - m.get())
			}
			m.Collect(ch)
		case *gauge:
			m.Set(unwrapScalarRMValue(sample.Value))
			m.Collect(ch)
		case *batchHistogram:
			m.update(sample.Value.Float64Histogram(), c.exactSumFor(sample.Name))
			m.Collect(ch)
		default:
			panic("unexpected metric type")
		}
	}

	if c.msMetricsEnabled {
		// ms is a dummy MemStats that we populate ourselves so that we can
		// populate the old metrics from it if goMemStatsCollection is enabled.