Generate unique entryID in atomic style

cron.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"runtime"
 	"sort"
+	"sync/atomic"
 	"time"
 )
 
@@ -19,7 +20,7 @@ type Cron struct {
 	snapshot chan []*Entry
 	running  bool
 	location *time.Location
-	nextID   EntryID
+	nextID   uint32
 	ErrorLog *log.Logger
 }
 
@@ -36,7 +37,7 @@ type Schedule interface {
 }
 
 // EntryID identifies an entry within a Cron instance
-type EntryID int
+type EntryID uint32
 
 // Entry consists of a schedule and the func to execute on that schedule.
 type Entry struct {
@@ -144,10 +145,10 @@ func (c *Cron) AddJobN(name, spec string, cmd Job) (EntryID, error) {
 
 // Schedule adds a Job to the Cron to be run on the given schedule.
 func (c *Cron) Schedule(schedule Schedule, cmd Job) EntryID {
-	c.nextID++
+	nextID := atomic.AddUint32(&c.nextID, 1)
 
 	entry := &Entry{
-		ID:       c.nextID,
+		ID:       EntryID(nextID),
 		Schedule: schedule,
 		Job:      cmd,
 	}
@@ -163,10 +164,10 @@ func (c *Cron) Schedule(schedule Schedule, cmd Job) EntryID {
 
 // ScheduleN adds a Job to the Cron to be run on the given schedule.
 func (c *Cron) ScheduleN(name, spec string, schedule Schedule, cmd Job) EntryID {
-	c.nextID++
+	nextID := atomic.AddUint32(&c.nextID, 1)
 
 	entry := &Entry{
-		ID:       c.nextID,
+		ID:       EntryID(nextID),
 		Name:     name,
 		Spec:     spec,
 		Schedule: schedule,

cron_test.go

@@ -161,6 +161,52 @@ func TestRemoveWhileRunning(t *testing.T) {
 	}
 }
 
+// Schedule within multiple go routines
+func TestParallelSchedule(t *testing.T) {
+	var wg sync.WaitGroup
+	const numRoutine = 4
+
+	errSlice := make([]error, numRoutine)
+	idSlice := make([][]EntryID, numRoutine)
+	cron := New()
+	cron.Start()
+	for i := 0; i < numRoutine; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			const numTry = 100
+			for iTry := 0; iTry < numTry; iTry++ {
+				sched, err := Parse("* * * * * ?")
+				if err != nil {
+					errSlice[i] = err
+					return
+				}
+				var job testJob
+				entryID := cron.Schedule(sched, job)
+				idSlice[i] = append(idSlice[i], entryID)
+			}
+		}(i)
+	}
+	wg.Wait()
+
+	for i, err := range errSlice {
+		if err != nil {
+			t.Fatal("Error in #", i, ":", err)
+		}
+	}
+
+	idMap := make(map[EntryID]bool)
+	for i, ids := range idSlice {
+		for j, id := range ids {
+			if idMap[id] {
+				t.Fatal("id duplicate in #", i, "No:", j, "id:", id)
+			}
+			idMap[id] = true
+		}
+	}
+	cron.Stop()
+}
+
 // Test timing with Entries.
 func TestSnapshotEntries(t *testing.T) {
 	wg := &sync.WaitGroup{}

go.mod

@@ -0,0 +1,3 @@
+module github.com/tangyanhan/cron
+
+go 1.13