limithandler: Split out monitor logic

The monitor logic is hosted in both the concurrency limiting code and in
the metrics code. Move it into a separate file to make it more
self-contained.

3 files changed, 82 insertions, 77 deletions

diff --git a/internal/middleware/limithandler/concurrency_limiter.go b/internal/middleware/limithandler/concurrency_limiter.go
index ab3a1cf3e..7088c7077 100644
--- a/internal/middleware/limithandler/concurrency_limiter.go
+++ b/internal/middleware/limithandler/concurrency_limiter.go
@@ -10,14 +10,6 @@ import (
 // LimitedFunc represents a function that will be limited
 type LimitedFunc func() (resp interface{}, err error)
 
-// ConcurrencyMonitor allows the concurrency monitor to be observed
-type ConcurrencyMonitor interface {
-	Queued(ctx context.Context)
-	Dequeued(ctx context.Context)
-	Enter(ctx context.Context, acquireTime time.Duration)
-	Exit(ctx context.Context)
-}
-
 // ConcurrencyLimiter contains rate limiter state
 type ConcurrencyLimiter struct {
 	semaphores map[string]*semaphoreReference
@@ -119,10 +111,3 @@ func NewLimiter(max int, monitor ConcurrencyMonitor) *ConcurrencyLimiter {
 		monitor:    monitor,
 	}
 }
-
-type nullConcurrencyMonitor struct{}
-
-func (c *nullConcurrencyMonitor) Queued(ctx context.Context)                           {}
-func (c *nullConcurrencyMonitor) Dequeued(ctx context.Context)                         {}
-func (c *nullConcurrencyMonitor) Enter(ctx context.Context, acquireTime time.Duration) {}
-func (c *nullConcurrencyMonitor) Exit(ctx context.Context)                             {}
diff --git a/internal/middleware/limithandler/metrics.go b/internal/middleware/limithandler/metrics.go
index 307d00944..77fd77137 100644
--- a/internal/middleware/limithandler/metrics.go
+++ b/internal/middleware/limithandler/metrics.go
@@ -1,17 +1,10 @@
 package limithandler
 
 import (
-	"context"
-	"strings"
-	"time"
-
-	"github.com/grpc-ecosystem/go-grpc-middleware/logging/logrus/ctxlogrus"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
-const acquireDurationLogThreshold = 10 * time.Millisecond
-
 var (
 	histogramVec       *prometheus.HistogramVec
 	inprogressGaugeVec = promauto.NewGaugeVec(
@@ -35,20 +28,6 @@ var (
 	)
 )
 
-type promMonitor struct {
-	queuedGauge     prometheus.Gauge
-	inprogressGauge prometheus.Gauge
-	histogram       prometheus.Observer
-}
-
-func splitMethodName(fullMethodName string) (string, string) {
-	fullMethodName = strings.TrimPrefix(fullMethodName, "/") // remove leading slash
-	if i := strings.Index(fullMethodName, "/"); i >= 0 {
-		return fullMethodName[:i], fullMethodName[i+1:]
-	}
-	return "unknown", "unknown"
-}
-
 // EnableAcquireTimeHistogram enables histograms for acquisition times
 func EnableAcquireTimeHistogram(buckets []float64) {
 	histogramOpts := prometheus.HistogramOpts{
@@ -64,44 +43,3 @@ func EnableAcquireTimeHistogram(buckets []float64) {
 		[]string{"system", "grpc_service", "grpc_method"},
 	)
 }
-
-func (c *promMonitor) Queued(ctx context.Context) {
-	c.queuedGauge.Inc()
-}
-
-func (c *promMonitor) Dequeued(ctx context.Context) {
-	c.queuedGauge.Dec()
-}
-
-func (c *promMonitor) Enter(ctx context.Context, acquireTime time.Duration) {
-	c.inprogressGauge.Inc()
-
-	if acquireTime > acquireDurationLogThreshold {
-		logger := ctxlogrus.Extract(ctx)
-		logger.WithField("acquire_ms", acquireTime.Seconds()*1000).Info("Rate limit acquire wait")
-	}
-
-	if c.histogram != nil {
-		c.histogram.Observe(acquireTime.Seconds())
-	}
-}
-
-func (c *promMonitor) Exit(ctx context.Context) {
-	c.inprogressGauge.Dec()
-}
-
-// NewPromMonitor creates a new ConcurrencyMonitor that tracks limiter
-// activity in Prometheus.
-func NewPromMonitor(system string, fullMethod string) ConcurrencyMonitor {
-	serviceName, methodName := splitMethodName(fullMethod)
-
-	queuedGauge := queuedGaugeVec.WithLabelValues(system, serviceName, methodName)
-	inprogressGauge := inprogressGaugeVec.WithLabelValues(system, serviceName, methodName)
-
-	var histogram prometheus.Observer
-	if histogramVec != nil {
-		histogram = histogramVec.WithLabelValues(system, serviceName, methodName)
-	}
-
-	return &promMonitor{queuedGauge, inprogressGauge, histogram}
-}
diff --git a/internal/middleware/limithandler/monitor.go b/internal/middleware/limithandler/monitor.go
new file mode 100644
index 000000000..8079eab37
--- /dev/null
+++ b/internal/middleware/limithandler/monitor.go
@@ -0,0 +1,82 @@
+package limithandler
+
+import (
+	"context"
+	"strings"
+	"time"
+
+	"github.com/grpc-ecosystem/go-grpc-middleware/logging/logrus/ctxlogrus"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const acquireDurationLogThreshold = 10 * time.Millisecond
+
+// ConcurrencyMonitor allows the concurrency monitor to be observed
+type ConcurrencyMonitor interface {
+	Queued(ctx context.Context)
+	Dequeued(ctx context.Context)
+	Enter(ctx context.Context, acquireTime time.Duration)
+	Exit(ctx context.Context)
+}
+
+type nullConcurrencyMonitor struct{}
+
+func (c *nullConcurrencyMonitor) Queued(ctx context.Context)                           {}
+func (c *nullConcurrencyMonitor) Dequeued(ctx context.Context)                         {}
+func (c *nullConcurrencyMonitor) Enter(ctx context.Context, acquireTime time.Duration) {}
+func (c *nullConcurrencyMonitor) Exit(ctx context.Context)                             {}
+
+type promMonitor struct {
+	queuedGauge     prometheus.Gauge
+	inprogressGauge prometheus.Gauge
+	histogram       prometheus.Observer
+}
+
+// NewPromMonitor creates a new ConcurrencyMonitor that tracks limiter
+// activity in Prometheus.
+func NewPromMonitor(system string, fullMethod string) ConcurrencyMonitor {
+	serviceName, methodName := splitMethodName(fullMethod)
+
+	queuedGauge := queuedGaugeVec.WithLabelValues(system, serviceName, methodName)
+	inprogressGauge := inprogressGaugeVec.WithLabelValues(system, serviceName, methodName)
+
+	var histogram prometheus.Observer
+	if histogramVec != nil {
+		histogram = histogramVec.WithLabelValues(system, serviceName, methodName)
+	}
+
+	return &promMonitor{queuedGauge, inprogressGauge, histogram}
+}
+
+func (c *promMonitor) Queued(ctx context.Context) {
+	c.queuedGauge.Inc()
+}
+
+func (c *promMonitor) Dequeued(ctx context.Context) {
+	c.queuedGauge.Dec()
+}
+
+func (c *promMonitor) Enter(ctx context.Context, acquireTime time.Duration) {
+	c.inprogressGauge.Inc()
+
+	if acquireTime > acquireDurationLogThreshold {
+		logger := ctxlogrus.Extract(ctx)
+		logger.WithField("acquire_ms", acquireTime.Seconds()*1000).Info("Rate limit acquire wait")
+	}
+
+	if c.histogram != nil {
+		c.histogram.Observe(acquireTime.Seconds())
+	}
+}
+
+func (c *promMonitor) Exit(ctx context.Context) {
+	c.inprogressGauge.Dec()
+}
+
+func splitMethodName(fullMethodName string) (string, string) {
+	fullMethodName = strings.TrimPrefix(fullMethodName, "/") // remove leading slash
+	if i := strings.Index(fullMethodName, "/"); i >= 0 {
+		return fullMethodName[:i], fullMethodName[i+1:]
+	}
+	return "unknown", "unknown"
+}