Queue: Add generic graceful queues with settings

modules/queue/queue_wrapped.go

@@ -0,0 +1,183 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package queue
+
+import (
+	"context"
+	"fmt"
+	"reflect"
+	"sync"
+	"time"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+// WrappedQueueType is the type for a wrapped delayed starting queue
+const WrappedQueueType Type = "wrapped"
+
+// WrappedQueueConfiguration is the configuration for a WrappedQueue
+type WrappedQueueConfiguration struct {
+	Underlying  Type
+	Timeout     time.Duration
+	MaxAttempts int
+	Config      interface{}
+	QueueLength int
+}
+
+type delayedStarter struct {
+	lock        sync.Mutex
+	internal    Queue
+	underlying  Type
+	cfg         interface{}
+	timeout     time.Duration
+	maxAttempts int
+}
+
+func (q *delayedStarter) setInternal(atShutdown func(context.Context, func()), handle HandlerFunc, exemplar interface{}) {
+	var ctx context.Context
+	var cancel context.CancelFunc
+	if q.timeout > 0 {
+		ctx, cancel = context.WithTimeout(context.Background(), q.timeout)
+	} else {
+		ctx, cancel = context.WithCancel(context.Background())
+	}
+
+	defer cancel()
+	// Ensure we also stop at shutdown
+	atShutdown(ctx, func() {
+		cancel()
+	})
+
+	i := 1
+	for q.internal == nil {
+		select {
+		case <-ctx.Done():
+			q.lock.Unlock()
+			log.Fatal("Timedout creating queue %v with cfg %v ", q.underlying, q.cfg)
+		default:
+			queue, err := CreateQueue(q.underlying, handle, q.cfg, exemplar)
+			if err == nil {
+				q.internal = queue
+				q.lock.Unlock()
+				break
+			}
+			if err.Error() != "resource temporarily unavailable" {
+				log.Warn("[Attempt: %d] Failed to create queue: %v cfg: %v error: %v", i, q.underlying, q.cfg, err)
+			}
+			i++
+			if q.maxAttempts > 0 && i > q.maxAttempts {
+				q.lock.Unlock()
+				log.Fatal("Unable to create queue %v with cfg %v by max attempts: error: %v", q.underlying, q.cfg, err)
+			}
+			sleepTime := 100 * time.Millisecond
+			if q.timeout > 0 && q.maxAttempts > 0 {
+				sleepTime = (q.timeout - 200*time.Millisecond) / time.Duration(q.maxAttempts)
+			}
+			time.Sleep(sleepTime)
+		}
+	}
+}
+
+// WrappedQueue wraps a delayed starting queue
+type WrappedQueue struct {
+	delayedStarter
+	handle   HandlerFunc
+	exemplar interface{}
+	channel  chan Data
+}
+
+// NewWrappedQueue will attempt to create a queue of the provided type,
+// but if there is a problem creating this queue it will instead create
+// a WrappedQueue with delayed the startup of the queue instead and a
+// channel which will be redirected to the queue
+func NewWrappedQueue(handle HandlerFunc, cfg, exemplar interface{}) (Queue, error) {
+	configInterface, err := toConfig(WrappedQueueConfiguration{}, cfg)
+	if err != nil {
+		return nil, err
+	}
+	config := configInterface.(WrappedQueueConfiguration)
+
+	queue, err := CreateQueue(config.Underlying, handle, config.Config, exemplar)
+	if err == nil {
+		// Just return the queue there is no need to wrap
+		return queue, nil
+	}
+	if IsErrInvalidConfiguration(err) {
+		// Retrying ain't gonna make this any better...
+		return nil, ErrInvalidConfiguration{cfg: cfg}
+	}
+
+	return &WrappedQueue{
+		handle:   handle,
+		channel:  make(chan Data, config.QueueLength),
+		exemplar: exemplar,
+		delayedStarter: delayedStarter{
+			cfg:         config.Config,
+			underlying:  config.Underlying,
+			timeout:     config.Timeout,
+			maxAttempts: config.MaxAttempts,
+		},
+	}, nil
+}
+
+// Push will push the data to the internal channel checking it against the exemplar
+func (q *WrappedQueue) Push(data Data) error {
+	if q.exemplar != nil {
+		// Assert data is of same type as r.exemplar
+		value := reflect.ValueOf(data)
+		t := value.Type()
+		exemplarType := reflect.ValueOf(q.exemplar).Type()
+		if !t.AssignableTo(exemplarType) || data == nil {
+			return fmt.Errorf("Unable to assign data: %v to same type as exemplar: %v in %s", data, q.exemplar, q.name)
+		}
+	}
+	q.channel <- data
+	return nil
+}
+
+// Run starts to run the queue and attempts to create the internal queue
+func (q *WrappedQueue) Run(atShutdown, atTerminate func(context.Context, func())) {
+	q.lock.Lock()
+	if q.internal == nil {
+		q.setInternal(atShutdown, q.handle, q.exemplar)
+		go func() {
+			for data := range q.channel {
+				_ = q.internal.Push(data)
+			}
+		}()
+	} else {
+		q.lock.Unlock()
+	}
+
+	q.internal.Run(atShutdown, atTerminate)
+}
+
+// Shutdown this queue and stop processing
+func (q *WrappedQueue) Shutdown() {
+	q.lock.Lock()
+	defer q.lock.Unlock()
+	if q.internal == nil {
+		return
+	}
+	if shutdownable, ok := q.internal.(Shutdownable); ok {
+		shutdownable.Shutdown()
+	}
+}
+
+// Terminate this queue and close the queue
+func (q *WrappedQueue) Terminate() {
+	q.lock.Lock()
+	defer q.lock.Unlock()
+	if q.internal == nil {
+		return
+	}
+	if shutdownable, ok := q.internal.(Shutdownable); ok {
+		shutdownable.Terminate()
+	}
+}
+
+func init() {
+	queuesMap[WrappedQueueType] = NewWrappedQueue
+}