Update docs for periodic tasks feature

CHANGELOG.md

@@ -7,7 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- `Scheduler` type is added to enable periodic tasks. See the godoc for its APIs and [wiki](https://github.com/hibiken/asynq/wiki/Periodic-Tasks) for the getting-started guide.
+
 ### Changed
+
 - interface `Option` has changed. See the godoc for the new interface.
   This change would have no impact as long as you are using exported functions (e.g. `MaxRetry`, `Queue`, etc)
   to create `Option`s.

README.md

@@ -42,6 +42,7 @@ A system can consist of multiple worker servers and brokers, giving way to high
 - Allow [timeout and deadline per task](https://github.com/hibiken/asynq/wiki/Task-Timeout-and-Cancelation)
 - [Flexible handler interface with support for middlewares](https://github.com/hibiken/asynq/wiki/Handler-Deep-Dive)
 - [Ability to pause queue](/tools/asynq/README.md#pause) to stop processing tasks from the queue
+- [Periodic Tasks](https://github.com/hibiken/asynq/wiki/Periodic-Tasks)
 - [Support Redis Cluster](https://github.com/hibiken/asynq/wiki/Redis-Cluster) for automatic sharding and high availability
 - [Support Redis Sentinels](https://github.com/hibiken/asynq/wiki/Automatic-Failover) for high availability
 - [CLI](#command-line-tool) to inspect and remote-control queues and tasks

example_test.go

@@ -9,6 +9,7 @@ import (
 	"log"
 	"os"
 	"os/signal"
+	"time"
 
 	"github.com/hibiken/asynq"
 	"golang.org/x/sys/unix"
@@ -78,6 +79,25 @@ func ExampleServer_Quiet() {
 	srv.Stop()
 }
 
+func ExampleScheduler() {
+	scheduler := asynq.NewScheduler(
+		asynq.RedisClientOpt{Addr: ":6379"},
+		&asynq.SchedulerOpts{Location: time.Local},
+	)
+
+	if _, err := scheduler.Register("* * * * *", asynq.NewTask("task1", nil)); err != nil {
+		log.Fatal(err)
+	}
+	if _, err := scheduler.Register("@every 30s", asynq.NewTask("task2", nil)); err != nil {
+		log.Fatal(err)
+	}
+
+	// Run blocks and waits for os signal to terminate the program.
+	if err := scheduler.Run(); err != nil {
+		log.Fatal(err)
+	}
+}
+
 func ExampleParseRedisURI() {
 	rconn, err := asynq.ParseRedisURI("redis://localhost:6379/10")
 	if err != nil {

scheduler.go

@@ -126,7 +126,7 @@ func (j *enqueueJob) Run() {
 	}
 }
 
-// Register registers a task to be enqueued with given schedule specified by the cronspec.
+// Register registers a task to be enqueued on the given schedule specified by the cronspec.
 // It returns an ID of the newly registered entry.
 func (s *Scheduler) Register(cronspec string, task *Task, opts ...Option) (entryID string, err error) {
 	job := &enqueueJob{

tools/asynq/cmd/cron.go

@@ -84,6 +84,7 @@ func prevEnqueue(prevEnqueuedAt time.Time) string {
 	return fmt.Sprintf("%v ago", time.Since(prevEnqueuedAt).Round(time.Second))
 }
 
+// TODO: Paginate the result set.
 func cronHistory(cmd *cobra.Command, args []string) {
 	r := createRDB()
 	for i, entryID := range args {