update the functionality for singleton mode jobs

example_test.go

@@ -862,6 +862,31 @@ func ExampleWithIdentifier() {
 	// 87b95dfc-3e71-11ef-9454-0242ac120002
 }
 
+func ExampleWithIntervalFromCompletion() {
+	s, _ := gocron.NewScheduler()
+	defer func() { _ = s.Shutdown() }()
+
+	_, _ = s.NewJob(
+		gocron.DurationJob(
+			5*time.Minute,
+		),
+		gocron.NewTask(
+			func() {
+				time.Sleep(30 * time.Second)
+			},
+		),
+		gocron.WithIntervalFromCompletion(),
+	)
+
+	// Without WithIntervalFromCompletion (default behavior):
+	// If the job starts at 00:00 and completes at 00:00:30,
+	// the next job starts at 00:05:00 (only 4m30s rest).
+
+	// With WithIntervalFromCompletion:
+	// If the job starts at 00:00 and completes at 00:00:30,
+	// the next job starts at 00:05:30 (full 5m rest).
+}
+
 func ExampleWithLimitConcurrentJobs() {
 	_, _ = gocron.NewScheduler(
 		gocron.WithLimitConcurrentJobs(
@@ -1016,31 +1041,6 @@ func ExampleWithSingletonMode() {
 	)
 }
 
-func ExampleWithIntervalFromCompletion() {
-	s, _ := gocron.NewScheduler()
-	defer func() { _ = s.Shutdown() }()
-
-	_, _ = s.NewJob(
-		gocron.DurationJob(
-			5*time.Minute,
-		),
-		gocron.NewTask(
-			func() {
-				time.Sleep(30 * time.Second)
-			},
-		),
-		gocron.WithIntervalFromCompletion(),
-	)
-
-	// Without WithIntervalFromCompletion (default behavior):
-	// If the job starts at 00:00 and completes at 00:00:30,
-	// the next job starts at 00:05:00 (only 4m30s rest).
-	
-	// With WithIntervalFromCompletion:
-	// If the job starts at 00:00 and completes at 00:00:30,
-	// the next job starts at 00:05:30 (full 5m rest).
-}
-
 func ExampleWithStartAt() {
 	s, _ := gocron.NewScheduler()
 	defer func() { _ = s.Shutdown() }()

executor.go

@@ -200,7 +200,10 @@ func (e *executor) start() {
 							select {
 							case runner.rescheduleLimiter <- struct{}{}:
 								runner.in <- jIn
-								e.sendOutForRescheduling(&jIn)
+								// For intervalFromCompletion, skip rescheduling here - it will happen after job completes
+								if !j.intervalFromCompletion {
+									e.sendOutForRescheduling(&jIn)
+								}
 							default:
 								// runner is busy, reschedule the work for later
 								// which means we just skip it here and do nothing
@@ -210,7 +213,10 @@ func (e *executor) start() {
 						} else {
 							// wait mode, fill up that queue (buffered channel, so it's ok)
 							runner.in <- jIn
-							e.sendOutForRescheduling(&jIn)
+							// For intervalFromCompletion, skip rescheduling here - it will happen after job completes
+							if !j.intervalFromCompletion {
+								e.sendOutForRescheduling(&jIn)
+							}
 						}
 					} else {
 						select {
@@ -345,7 +351,10 @@ func (e *executor) singletonModeRunner(name string, in chan jobIn, wg *waitGroup
 				// need to set shouldSendOut = false here, as there is a duplicative call to sendOutForRescheduling
 				// inside the runJob function that needs to be skipped. sendOutForRescheduling is previously called
 				// when the job is sent to the singleton mode runner.
-				jIn.shouldSendOut = false
+				// Exception: for intervalFromCompletion, we want rescheduling to happen AFTER job completion
+				if !j.intervalFromCompletion {
+					jIn.shouldSendOut = false
+				}
 				e.runJob(*j, jIn)
 			}
 

job.go

@@ -701,7 +701,7 @@ func WithSingletonMode(mode LimitMode) JobOption {
 // Note: This option only makes sense with interval-based jobs (DurationJob, DurationRandomJob).
 // For time-based jobs (CronJob, DailyJob, etc.) that run at specific times, this option
 // will be ignored as those jobs are inherently scheduled at fixed times.
-// 
+//
 // Example:
 //
 //	s.NewJob(

job_test.go

@@ -964,13 +964,18 @@ func TestWithIntervalFromCompletion_LongRunningJob(t *testing.T) {
 	// Execution 1: 0s-6s, wait 3s → next at 9s
 	// Execution 2: 9s-15s, wait 3s → next at 18s
 	// Need to wait at least 16 seconds for 2 executions + buffer
-	time.Sleep(20 * time.Second)
+	time.Sleep(22 * time.Second)
 
 	mu.Lock()
 	defer mu.Unlock()
 
 	require.GreaterOrEqual(t, len(executions), 2, "Expected at least 2 executions")
 
+	if len(executions) < 2 {
+		t.Logf("Only got %d execution(s), skipping gap assertion", len(executions))
+		return
+	}
+
 	prev := executions[0]
 	curr := executions[1]
 

scheduler.go

@@ -347,7 +347,7 @@ func (s *scheduler) selectExecJobsOutForRescheduling(id uuid.UUID) {
 	}
 
 	var scheduleFrom time.Time
-	
+
 	// If intervalFromCompletion is enabled, calculate the next run time
 	// from when the job completed (lastRun) rather than when it was scheduled.
 	if j.intervalFromCompletion {