diff --git a/goccm.go b/goccm.go
index 737e700..09ddbd2 100644
--- a/goccm.go
+++ b/goccm.go
@@ -34,8 +34,8 @@ type (
 		// This channel indicates when all goroutines have finished their job.
 		allDoneCh chan bool
 
-		// The close flag allows we know when we can close the manager
-		closed bool
+		// The closed channel is closed which controller should close
+		closed chan bool
 
 		// The running count allows we know the number of goroutines are running
 		runningCount int32
@@ -50,6 +50,7 @@ func New(maxGoRoutines int) *concurrencyManager {
 		managerCh: make(chan interface{}, maxGoRoutines),
 		doneCh:    make(chan bool),
 		allDoneCh: make(chan bool),
+		closed:    make(chan bool),
 	}
 
 	// Fill the manager channel by placeholder values
@@ -75,7 +76,7 @@ func (c *concurrencyManager) controller() {
 
 		// When the closed flag is set,
 		// we need to close the manager if it doesn't have any running goroutine
-		if c.closed && c.runningCount == 0 {
+		if c.IsClosed() && c.RunningCount() == 0 {
 			break
 		}
 	}
@@ -105,8 +106,24 @@ func (c *concurrencyManager) Done() {
 }
 
 // Close the manager manually
+// terminate if channel is already closed
 func (c *concurrencyManager) Close() {
-	c.closed = true
+	// terminate if channel is already closed
+	select {
+	case <-c.closed:
+		return
+	default:
+		close(c.closed)
+	}
+}
+
+func (c *concurrencyManager) IsClosed() bool {
+	select {
+	case <-c.closed:
+		return true
+	default:
+		return false
+	}
 }
 
 // WaitAllDone Wait for all goroutines are done
@@ -120,5 +137,5 @@ func (c *concurrencyManager) WaitAllDone() {
 
 // RunningCount Returns the number of goroutines which are running
 func (c *concurrencyManager) RunningCount() int32 {
-	return c.runningCount
+	return atomic.AddInt32(&c.runningCount, 0)
 }
diff --git a/goccm_test.go b/goccm_test.go
index baebda1..6a44c38 100644
--- a/goccm_test.go
+++ b/goccm_test.go
@@ -2,6 +2,7 @@ package goccm
 
 import (
 	"fmt"
+	"log"
 	"testing"
 	"time"
 )
@@ -12,25 +13,31 @@ func TestExample(t *testing.T) {
 		c.Wait()
 		go func(i int) {
 			fmt.Printf("Job %d is running\n", i)
-			time.Sleep(2 * time.Second)
+			time.Sleep(20 * time.Millisecond)
 			c.Done()
 		}(i)
 	}
 	c.WaitAllDone()
 }
 
+// TestManuallyClose will close after 5 jobs, others should not run
 func TestManuallyClose(t *testing.T) {
-	executedJobs := 0
+	executedJobs := make(chan int, 1000)
+
 	c := New(3)
 	for i := 1; i <= 1000; i++ {
+		jobId := i
+
 		c.Wait()
 		go func() {
-			executedJobs++
-			fmt.Printf("Executed jobs %d\n", executedJobs)
-			time.Sleep(2 * time.Second)
+			executedJobs <- jobId
+			fmt.Printf("Executed job id %d\n", jobId)
+			time.Sleep(20 * time.Millisecond)
 			c.Done()
 		}()
+
 		if i == 5 {
+			log.Printf("Closing manager")
 			c.Close()
 			break
 		}
@@ -40,21 +47,26 @@ func TestManuallyClose(t *testing.T) {
 
 func TestConcurrency(t *testing.T) {
 	var maxRunningJobs = 3
-	var testMaxRunningJobs int32
+	testMaxRunningJobs := make(chan int32, 100)
 	c := New(maxRunningJobs)
+
 	for i := 1; i <= 10; i++ {
 		c.Wait()
 		go func(i int) {
 			fmt.Printf("Current running jobs %d\n", c.RunningCount())
-			if c.RunningCount() > testMaxRunningJobs {
-				testMaxRunningJobs = c.RunningCount()
-			}
-			time.Sleep(2 * time.Second)
+			testMaxRunningJobs <- c.RunningCount()
+			time.Sleep(20 * time.Millisecond)
 			c.Done()
 		}(i)
 	}
+
 	c.WaitAllDone()
-	if testMaxRunningJobs > int32(maxRunningJobs) {
-		t.Errorf("The number of concurrency jobs has exceeded %d. Real result %d.", maxRunningJobs, testMaxRunningJobs)
+
+	for i := 1; i <= 10; i++ {
+		observed := <-testMaxRunningJobs
+
+		if observed > int32(maxRunningJobs) {
+			t.Errorf("The number of concurrency jobs has exceeded %d. Real result %d.", maxRunningJobs, testMaxRunningJobs)
+		}
 	}
 }