Method Gather

prometheus/registry.go:412–560

Gather implements Gatherer.

()

// Gather implements Gatherer.
func (r *Registry) Gather() ([]*dto.MetricFamily, error) {
	r.mtx.RLock()

	if len(r.collectorsByID) == 0 && len(r.uncheckedCollectors) == 0 {
		// Fast path.
		r.mtx.RUnlock()
		return nil, nil
	}

	var (
		checkedMetricChan   = make(chan Metric, capMetricChan)
		uncheckedMetricChan = make(chan Metric, capMetricChan)
		metricHashes        = map[uint64]struct{}{}
		wg                  sync.WaitGroup
		errs                MultiError          // The collected errors to return in the end.
		registeredDescIDs   map[uint64]struct{} // Only used for pedantic checks
	)

	goroutineBudget := len(r.collectorsByID) + len(r.uncheckedCollectors)
	metricFamiliesByName := make(map[string]*dto.MetricFamily, len(r.dimHashesByName))
	checkedCollectors := make(chan Collector, len(r.collectorsByID))
	uncheckedCollectors := make(chan Collector, len(r.uncheckedCollectors))
	for _, collector := range r.collectorsByID {
		checkedCollectors <- collector
	}
	for _, collector := range r.uncheckedCollectors {
		uncheckedCollectors <- collector
	}
	// In case pedantic checks are enabled, we have to copy the map before
	// giving up the RLock.
	if r.pedanticChecksEnabled {
		registeredDescIDs = make(map[uint64]struct{}, len(r.descIDs))
		for id := range r.descIDs {
			registeredDescIDs[id] = struct{}{}
		}
	}
	r.mtx.RUnlock()

	wg.Add(goroutineBudget)

	collectWorker := func() {
		for {
			select {
			case collector := <-checkedCollectors:
				collector.Collect(checkedMetricChan)
			case collector := <-uncheckedCollectors:
				collector.Collect(uncheckedMetricChan)
			default:
				return
			}
			wg.Done()
		}
	}

	// Start the first worker now to make sure at least one is running.
	go collectWorker()
	goroutineBudget--