promql.Engine: Add Close method

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

cmd/prometheus/main.go

@@ -942,12 +942,14 @@ func main() {
 	listener, err := webHandler.Listener()
 	if err != nil {
 		level.Error(logger).Log("msg", "Unable to start web listener", "err", err)
+		_ = queryEngine.Close()
 		os.Exit(1)
 	}
 
 	err = toolkit_web.Validate(*webConfig)
 	if err != nil {
 		level.Error(logger).Log("msg", "Unable to validate web configuration file", "err", err)
+		_ = queryEngine.Close()
 		os.Exit(1)
 	}
 
@@ -969,6 +971,7 @@ func main() {
 				case <-cancel:
 					reloadReady.Close()
 				}
+				_ = queryEngine.Close()
 				return nil
 			},
 			func(err error) {

promql/bench_test.go

@@ -21,6 +21,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/require"
+
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/promql"
@@ -257,6 +259,9 @@ func BenchmarkRangeQuery(b *testing.B) {
 		Timeout:    100 * time.Second,
 	}
 	engine := promql.NewEngine(opts)
+	b.Cleanup(func() {
+		require.NoError(b, engine.Close())
+	})
 
 	const interval = 10000 // 10s interval.
 	// A day of data plus 10k steps.
@@ -340,6 +345,9 @@ func BenchmarkNativeHistograms(b *testing.B) {
 	for _, tc := range cases {
 		b.Run(tc.name, func(b *testing.B) {
 			ng := promql.NewEngine(opts)
+			b.Cleanup(func() {
+				require.NoError(b, ng.Close())
+			})
 			for i := 0; i < b.N; i++ {
 				qry, err := ng.NewRangeQuery(context.Background(), testStorage, nil, tc.query, start, end, step)
 				if err != nil {

promql/engine.go

@@ -19,6 +19,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"math"
 	"reflect"
 	"runtime"
@@ -271,6 +272,8 @@ func contextErr(err error, env string) error {
 //
 // 2) Enforcement of the maximum number of concurrent queries.
 type QueryTracker interface {
+	io.Closer
+
 	// GetMaxConcurrent returns maximum number of concurrent queries that are allowed by this tracker.
 	GetMaxConcurrent() int
 
@@ -423,6 +426,11 @@ func NewEngine(opts EngineOpts) *Engine {
 	}
 }
 
+// Close closes ng.
+func (ng *Engine) Close() error {
+	return ng.activeQueryTracker.Close()
+}
+
 // SetQueryLogger sets the query logger.
 func (ng *Engine) SetQueryLogger(l QueryLogger) {
 	ng.queryLoggerLock.Lock()