Introduce Task Results

* Added Retention Option to specify retention TTL for tasks
* Added ResultWriter as a client interface to write result data for the associated task

janitor.go

@@ -0,0 +1,81 @@
+// Copyright 2021 Kentaro Hibino. All rights reserved.
+// Use of this source code is governed by a MIT license
+// that can be found in the LICENSE file.
+
+package asynq
+
+import (
+	"sync"
+	"time"
+
+	"github.com/hibiken/asynq/internal/base"
+	"github.com/hibiken/asynq/internal/log"
+)
+
+// A janitor is responsible for deleting expired completed tasks from the specified
+// queues. It periodically checks for any expired tasks in the completed set, and
+// deletes them.
+type janitor struct {
+	logger *log.Logger
+	broker base.Broker
+
+	// channel to communicate back to the long running "janitor" goroutine.
+	done chan struct{}
+
+	// list of queue names to check.
+	queues []string
+
+	// average interval between checks.
+	avgInterval time.Duration
+}
+
+type janitorParams struct {
+	logger   *log.Logger
+	broker   base.Broker
+	queues   []string
+	interval time.Duration
+}
+
+func newJanitor(params janitorParams) *janitor {
+	return &janitor{
+		logger:      params.logger,
+		broker:      params.broker,
+		done:        make(chan struct{}),
+		queues:      params.queues,
+		avgInterval: params.interval,
+	}
+}
+
+func (j *janitor) shutdown() {
+	j.logger.Debug("Janitor shutting down...")
+	// Signal the janitor goroutine to stop.
+	j.done <- struct{}{}
+}
+
+// start starts the "janitor" goroutine.
+func (j *janitor) start(wg *sync.WaitGroup) {
+	wg.Add(1)
+	timer := time.NewTimer(j.avgInterval) // randomize this interval with margin of 1s
+	go func() {
+		defer wg.Done()
+		for {
+			select {
+			case <-j.done:
+				j.logger.Debug("Janitor done")
+				return
+			case <-timer.C:
+				j.exec()
+				timer.Reset(j.avgInterval)
+			}
+		}
+	}()
+}
+
+func (j *janitor) exec() {
+	for _, qname := range j.queues {
+		if err := j.broker.DeleteExpiredCompletedTasks(qname); err != nil {
+			j.logger.Errorf("Could not delete expired completed tasks from queue %q: %v",
+				qname, err)
+		}
+	}
+}