diff --git a/builder.go b/builder.go
index f38db51..3c25702 100644
--- a/builder.go
+++ b/builder.go
@@ -1,7 +1,7 @@
 package cloudmap
 
 import (
-	"sync"
+	"context"
 	"time"
 
 	"google.golang.org/grpc/grpclog"
@@ -37,11 +37,11 @@ type builder struct {
 // so you don't need to call this function to register the default builder.
 //
 // Default Options:
+//
 //	Session: session.NewSession()
 //	HealthStatusFilter: HealthStatusFilterHealthy
 //	MaxResults: 100
 //	RefreshInterval: 30s
-//
 func Register(opts ...Opt) {
 	b := &builder{
 		healthStatusFilter: HealthStatusFilterHealthy,
@@ -72,23 +72,26 @@ func (b *builder) Build(t grpcresolver.Target, cc grpcresolver.ClientConn, _ grp
 		}
 	}
 
+	ctx, cancel := context.WithCancel(context.Background())
 	r := &resolver{
-		mu: &sync.RWMutex{},
-
 		logger: grpclog.Component(b.Scheme()),
 
 		cc: cc,
 
-		ticker: time.NewTicker(b.refreshInterval),
-
 		sd:                 servicediscovery.New(sess),
 		namespace:          cmT.namespace,
 		service:            cmT.service,
 		healthStatusFilter: b.healthStatusFilter,
 		maxResults:         b.maxResults,
+
+		ctx:        ctx,
+		cancel:     cancel,
+		ticker:     time.NewTicker(b.refreshInterval),
+		resolveCmd: make(chan struct{}, 1),
 	}
 
-	go r.watch()
+	r.wg.Add(1)
+	go r.watcher()
 
 	return r, nil
 }
diff --git a/resolver.go b/resolver.go
index 1c1c5d1..1fbcba7 100644
--- a/resolver.go
+++ b/resolver.go
@@ -1,6 +1,7 @@
 package cloudmap
 
 import (
+	"context"
 	"fmt"
 	"sync"
 	"time"
@@ -14,34 +15,35 @@ import (
 	"github.com/aws/aws-sdk-go/service/servicediscovery"
 )
 
-type resolver struct {
-	mu       *sync.RWMutex
-	isClosed bool
+type serviceDiscovery interface {
+	DiscoverInstances(input *servicediscovery.DiscoverInstancesInput) (*servicediscovery.DiscoverInstancesOutput, error)
+}
 
+type resolver struct {
 	logger grpclog.LoggerV2
+	cc     grpcresolver.ClientConn
 
-	cc grpcresolver.ClientConn
-
-	ticker *time.Ticker
-
-	sd                 *servicediscovery.ServiceDiscovery
+	sd                 serviceDiscovery
 	namespace          string
 	service            string
 	healthStatusFilter string
 	maxResults         int64
+
+	ctx        context.Context
+	cancel     context.CancelFunc
+	ticker     *time.Ticker
+	resolveCmd chan struct{}
+	wg         sync.WaitGroup
 }
 
 func (c *resolver) ResolveNow(grpcresolver.ResolveNowOptions) {
-	locked := c.mu.TryLock()
-	if !locked { // already resolving
-		return
-	}
-	defer c.mu.Unlock()
-
-	if c.isClosed {
-		return
+	select {
+	case c.resolveCmd <- struct{}{}:
+	default:
 	}
+}
 
+func (c *resolver) lookupCloudmap() (*grpcresolver.State, error) {
 	output, err := c.sd.DiscoverInstances(&servicediscovery.DiscoverInstancesInput{
 		NamespaceName: aws.String(c.namespace),
 		ServiceName:   aws.String(c.service),
@@ -65,8 +67,7 @@ func (c *resolver) ResolveNow(grpcresolver.ResolveNowOptions) {
 		} else {
 			c.logger.Errorln(err.Error())
 		}
-		c.cc.ReportError(err)
-		return
+		return nil, err
 	}
 
 	addrs := make([]grpcresolver.Address, len(output.Instances))
@@ -74,25 +75,37 @@ func (c *resolver) ResolveNow(grpcresolver.ResolveNowOptions) {
 		addrs[i] = httpInstanceSummaryToAddr(instance)
 	}
 
-	c.cc.UpdateState(grpcresolver.State{Addresses: addrs})
+	return &grpcresolver.State{Addresses: addrs}, nil
 }
 
 func (c *resolver) Close() {
-	c.mu.Lock()
-	defer c.mu.Unlock()
-
-	if c.isClosed {
-		return
-	}
-
-	c.isClosed = true
+	c.cancel()
 	c.ticker.Stop()
+	c.wg.Wait()
 }
 
-func (c *resolver) watch() {
+func (c *resolver) watcher() {
+	defer c.wg.Done()
+
 	for {
-		c.ResolveNow(grpcresolver.ResolveNowOptions{})
-		<-c.ticker.C
+		state, err := c.lookupCloudmap()
+		if err != nil {
+			c.cc.ReportError(err)
+		} else {
+			err = c.cc.UpdateState(*state)
+		}
+
+		if err != nil {
+			c.logger.Errorln(err)
+			// wait for next iteration
+		}
+
+		select {
+		case <-c.ctx.Done():
+			return
+		case <-c.ticker.C:
+		case <-c.resolveCmd:
+		}
 	}
 }
 
diff --git a/resolver_test.go b/resolver_test.go
new file mode 100644
index 0000000..b845d4c
--- /dev/null
+++ b/resolver_test.go
@@ -0,0 +1,70 @@
+package cloudmap
+
+import (
+	"context"
+	"fmt"
+	"github.com/aws/aws-sdk-go/service/servicediscovery"
+	"google.golang.org/grpc/grpclog"
+	grpcresolver "google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/serviceconfig"
+	"testing"
+	"time"
+)
+
+type mockCC struct{}
+
+func (m mockCC) UpdateState(state grpcresolver.State) error { return nil }
+
+func (m mockCC) ReportError(err error) {}
+
+func (m mockCC) NewAddress(addresses []grpcresolver.Address) {}
+
+func (m mockCC) NewServiceConfig(serviceConfig string) {}
+
+func (m mockCC) ParseServiceConfig(serviceConfigJSON string) *serviceconfig.ParseResult {
+	return nil
+}
+
+type mockDiscovery struct{}
+
+func (m mockDiscovery) DiscoverInstances(input *servicediscovery.DiscoverInstancesInput) (*servicediscovery.DiscoverInstancesOutput, error) {
+	time.Sleep(1 * time.Second)
+	fmt.Println("DiscoverInstances called")
+	return &servicediscovery.DiscoverInstancesOutput{
+		Instances: make([]*servicediscovery.HttpInstanceSummary, 0),
+	}, nil
+}
+
+func Test_resolver(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	r := &resolver{
+		logger: grpclog.Component("test"),
+
+		cc: mockCC{},
+		sd: mockDiscovery{},
+
+		ctx:        ctx,
+		cancel:     cancel,
+		ticker:     time.NewTicker(10 * time.Second),
+		resolveCmd: make(chan struct{}, 1),
+	}
+
+	r.wg.Add(1)
+	go r.watcher()
+
+	timeout := time.After(100 * time.Millisecond)
+	done := make(chan bool)
+	go func() {
+		for i := 0; i < 10; i++ {
+			r.ResolveNow(grpcresolver.ResolveNowOptions{})
+		}
+		done <- true
+	}()
+	select {
+	case <-timeout:
+		t.Error("timeout")
+	case <-done:
+		t.Log("done")
+	}
+	r.Close()
+}