Supporting customize Timer to control the scheduling behavior

Thanks to PR robfig/cron#491

Author: dsh2dsh

cron.go

@@ -24,6 +24,8 @@ type Cron struct {
 	parser    ScheduleParser
 	nextID    EntryID
 	jobWaiter sync.WaitGroup
+
+	timerFn func(d time.Duration) Timer
 }
 
 // ScheduleParser is an interface for schedule spec parsers that return a Schedule
@@ -123,6 +125,7 @@ func New(opts ...Option) *Cron {
 		logger:    DefaultLogger,
 		location:  time.Local,
 		parser:    standardParser,
+		timerFn:   newStdTimer,
 	}
 	for _, opt := range opts {
 		opt(c)
@@ -250,7 +253,7 @@ func (c *Cron) run() {
 		c.logger.Info("schedule", "now", now, "entry", entry.ID, "next", entry.Next)
 	}
 
-	var timer *time.Timer
+	var timer Timer
 	for {
 		// Determine the next entry to run.
 		slices.SortFunc(c.entries, func(a, b *Entry) int { return a.Cmp(b) })
@@ -265,15 +268,15 @@ func (c *Cron) run() {
 		}
 
 		if timer == nil {
-			timer = time.NewTimer(d)
+			timer = c.timerFn(d)
 		} else {
 			timer.Reset(d)
 		}
 
 		var stopTimer bool
 		for {
 			select {
-			case now = <-timer.C:
+			case now = <-timer.C():
 				now = now.In(c.location)
 				c.logger.Info("wake", "now", now)
 
@@ -314,7 +317,7 @@ func (c *Cron) run() {
 		}
 
 		if stopTimer && !timer.Stop() {
-			<-timer.C
+			<-timer.C()
 		}
 	}
 }

option.go

@@ -1,8 +1,6 @@
 package cron
 
-import (
-	"time"
-)
+import "time"
 
 // Option represents a modification to the default behavior of a Cron.
 type Option func(*Cron)
@@ -43,3 +41,9 @@ func WithLogger(logger Logger) Option {
 		c.logger = logger
 	}
 }
+
+// WithTimer specifies a [Timer] creator. If not specified, [time.Timer] will be
+// used by default. Refer to the [Timer] documentation for details.
+func WithTimer(fn func(time.Duration) Timer) Option {
+	return func(c *Cron) { c.timerFn = fn }
+}

option_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -43,3 +44,15 @@ func TestWithVerboseLogger(t *testing.T) {
 		t.Error("expected to see some actions, got:", out)
 	}
 }
+
+func TestWithTimer(t *testing.T) {
+	var called bool
+	timerFn := func(d time.Duration) Timer {
+		called = true
+		return newStdTimer(d)
+	}
+	c := New(WithTimer(timerFn))
+	c.Start()
+	<-c.Stop().Done()
+	assert.True(t, called)
+}

timer.go

@@ -0,0 +1,28 @@
+package cron
+
+import "time"
+
+// A Timer works just like [time.Timer], and cron schedules [Jobs] by waiting
+// for the time event emitted by Timer. By default, [time.Timer] is used. You
+// can also customize a Timer with [WithTimer] option to control scheduling
+// behavior.
+type Timer interface {
+	C() <-chan time.Time
+	Reset(d time.Duration) bool
+	Stop() bool
+}
+
+// newStdTimer returns a Timer created using [time.Timer].
+func newStdTimer(d time.Duration) Timer {
+	return &stdTimer{t: time.NewTimer(d)}
+}
+
+type stdTimer struct {
+	t *time.Timer
+}
+
+func (self *stdTimer) C() <-chan time.Time { return self.t.C }
+
+func (self *stdTimer) Reset(d time.Duration) bool { return self.t.Reset(d) }
+
+func (self *stdTimer) Stop() bool { return self.t.Stop() }