func (ps *PubSub[T, M]) Subscribe(mask M, subCh chan T, doneCh <-chan struct{}, filter func(entry T) bool) error {
	totalSubs := atomic.AddInt32(&ps.numSubscribers, 1)
	if ps.maxSubscribers > 0 && totalSubs > ps.maxSubscribers {
		atomic.AddInt32(&ps.numSubscribers, -1)
		return fmt.Errorf("the limit of `%d` subscribers is reached", ps.maxSubscribers)
	}
	ps.Lock()
	defer ps.Unlock()

	if len(ps.subs) != 2 {
		t.Fatalf("expected 2 subscribers")
	}
	if want, got := int32(2), ps.NumSubscribers(Mask(1)); got != want {
		t.Fatalf("want %d subscribers, got %d", want, got)
	}
	if want, got := int32(2), ps.NumSubscribers(Mask(2)); got != want {
		t.Fatalf("want %d subscribers, got %d", want, got)
	}
	if want, got := int32(2), ps.NumSubscribers(Mask(1|2)); got != want {
		t.Fatalf("want %d subscribers, got %d", want, got)
	}

}

const (
	httpScheme  = "http://"
	httpsScheme = "https://"
)

func (c *muxClient) traceRoundtrip(ctx context.Context, t *tracer, h HandlerID, req []byte) ([]byte, error) {
	if t == nil || t.Publisher.NumSubscribers(t.TraceType) == 0 {
		return c.roundtrip(h, req)
	}

	// Following trimming is needed for consistency between outputs with other internode traces.

	// remove sensitive encryption entries in metadata.
	crypto.RemoveSensitiveEntries(args.Object.UserDefined)
	crypto.RemoveInternalEntries(args.Object.UserDefined)

	if globalHTTPListen.NumSubscribers(pubsub.MaskFromMaskable(args.EventName)) > 0 {
		globalHTTPListen.Publish(args.ToEvent(false))
	}

	globalEventNotifier.Send(args)

		}

		r = r.WithContext(context.WithValue(r.Context(), mcontext.ContextTraceKey, &tc))

		reqStartTime := time.Now().UTC()
		h.ServeHTTP(respRecorder, r)
		reqEndTime := time.Now().UTC()

		if globalTrace.NumSubscribers(madmin.TraceS3|madmin.TraceInternal) == 0 {
			// no subscribers nothing to trace.
			return
		}

		tt := madmin.TraceInternal
		if strings.HasPrefix(tc.FuncName, "s3.") {
			tt = madmin.TraceS3
		}

		FuncName:  "os." + s.String(),
		Duration:  duration,
		Path:      path,
		Error:     errStr,
	}
}

func updateOSMetrics(s osMetric, paths ...string) func(err error) {
	if globalTrace.NumSubscribers(madmin.TraceOS) == 0 {
		osAction := globalOSMetrics.time(s)
		return func(err error) { osAction() }
	}

	startTime := time.Now()
	return func(err error) {
		duration := time.Since(startTime)

		duration := time.Since(startTime)

		atomic.AddUint64(&p.operations[s], 1)
		if s < scannerMetricLastRealtime {
			p.latency[s].add(duration)
		}

		if s > scannerMetricStartTrace && globalTrace.NumSubscribers(madmin.TraceScanner) > 0 {
			globalTrace.Publish(scannerTrace(s, startTime, duration, strings.Join(paths, " "), custom))
		}
	}
}

// time n scanner actions.
// Use for s < scannerMetricLastRealtime