feat: concurrency control queue

internal/rdb/rdb.go

@@ -24,18 +24,31 @@ const statsTTL = 90 * 24 * time.Hour // 90 days
 // LeaseDuration is the duration used to initially create a lease and to extend it thereafter.
 const LeaseDuration = 30 * time.Second
 
+type Option func(r *RDB)
+
+func WithQueueConcurrency(queueConcurrency map[string]int) Option {
+	return func(r *RDB) {
+		r.queueConcurrency = queueConcurrency
+	}
+}
+
 // RDB is a client interface to query and mutate task queues.
 type RDB struct {
-	client redis.UniversalClient
-	clock  timeutil.Clock
+	client           redis.UniversalClient
+	clock            timeutil.Clock
+	queueConcurrency map[string]int
 }
 
 // NewRDB returns a new instance of RDB.
-func NewRDB(client redis.UniversalClient) *RDB {
-	return &RDB{
+func NewRDB(client redis.UniversalClient, opts ...Option) *RDB {
+	r := &RDB{
 		client: client,
 		clock:  timeutil.NewRealClock(),
 	}
+	for _, opt := range opts {
+		opt(r)
+	}
+	return r
 }
 
 // Close closes the connection with redis server.
@@ -209,6 +222,7 @@ func (r *RDB) EnqueueUnique(ctx context.Context, msg *base.TaskMessage, ttl time
 // --
 // ARGV[1] -> initial lease expiration Unix time
 // ARGV[2] -> task key prefix
+// ARGV[3] -> queue concurrency
 //
 // Output:
 // Returns nil if no processable task is found in the given queue.
@@ -217,15 +231,20 @@ func (r *RDB) EnqueueUnique(ctx context.Context, msg *base.TaskMessage, ttl time
 // Note: dequeueCmd checks whether a queue is paused first, before
 // calling RPOPLPUSH to pop a task from the queue.
 var dequeueCmd = redis.NewScript(`
-if redis.call("EXISTS", KEYS[2]) == 0 then
-	local id = redis.call("RPOPLPUSH", KEYS[1], KEYS[3])
-	if id then
-		local key = ARGV[2] .. id
-		redis.call("HSET", key, "state", "active")
-		redis.call("HDEL", key, "pending_since")
-		redis.call("ZADD", KEYS[4], ARGV[1], id)
-		return redis.call("HGET", key, "msg")
-	end
+if redis.call("EXISTS", KEYS[2]) > 0 then
+	return nil
+end
+local count = redis.call("ZCARD", KEYS[4])
+if (count >= tonumber(ARGV[3])) then
+     return nil
+end
+local id = redis.call("RPOPLPUSH", KEYS[1], KEYS[3])
+if id then
+	local key = ARGV[2] .. id
+	redis.call("HSET", key, "state", "active")
+	redis.call("HDEL", key, "pending_since")
+	redis.call("ZADD", KEYS[4], ARGV[1], id)
+	return redis.call("HGET", key, "msg")
 end
 return nil`)
 
@@ -243,9 +262,14 @@ func (r *RDB) Dequeue(qnames ...string) (msg *base.TaskMessage, leaseExpirationT
 			base.LeaseKey(qname),
 		}
 		leaseExpirationTime = r.clock.Now().Add(LeaseDuration)
+		queueConcurrency, ok := r.queueConcurrency[qname]
+		if !ok || queueConcurrency <= 0 {
+			queueConcurrency = math.MaxInt
+		}
 		argv := []interface{}{
 			leaseExpirationTime.Unix(),
 			base.TaskKeyPrefix(qname),
+			queueConcurrency,
 		}
 		res, err := dequeueCmd.Run(context.Background(), r.client, keys, argv...).Result()
 		if err == redis.Nil {

internal/rdb/rdb_test.go

@@ -331,6 +331,7 @@ func TestDequeue(t *testing.T) {
 		wantPending        map[string][]*base.TaskMessage
 		wantActive         map[string][]*base.TaskMessage
 		wantLease          map[string][]base.Z
+		queueConcurrency   map[string]int
 	}{
 		{
 			pending: map[string][]*base.TaskMessage{
@@ -441,6 +442,86 @@ func TestDequeue(t *testing.T) {
 	}
 }
 
+func TestDequeueWithQueueConcurrency(t *testing.T) {
+	r := setup(t)
+	defer r.Close()
+	now := time.Now()
+	r.SetClock(timeutil.NewSimulatedClock(now))
+	const taskNum = 3
+	msgs := make([]*base.TaskMessage, 0, taskNum)
+	for i := 0; i < taskNum; i++ {
+		msg := &base.TaskMessage{
+			ID:       uuid.NewString(),
+			Type:     "send_email",
+			Payload:  h.JSON(map[string]interface{}{"subject": "hello!"}),
+			Queue:    "default",
+			Timeout:  1800,
+			Deadline: 0,
+		}
+		msgs = append(msgs, msg)
+	}
+
+	tests := []struct {
+		name             string
+		pending          map[string][]*base.TaskMessage
+		qnames           []string // list of queues to query
+		queueConcurrency map[string]int
+		wantMsgs         []*base.TaskMessage
+	}{
+		{
+			name: "without queue concurrency control",
+			pending: map[string][]*base.TaskMessage{
+				"default": msgs,
+			},
+			qnames:   []string{"default"},
+			wantMsgs: msgs,
+		},
+		{
+			name: "with queue concurrency control",
+			pending: map[string][]*base.TaskMessage{
+				"default": msgs,
+			},
+			qnames:           []string{"default"},
+			queueConcurrency: map[string]int{"default": 2},
+			wantMsgs:         msgs[:2],
+		},
+		{
+			name: "with queue concurrency zero",
+			pending: map[string][]*base.TaskMessage{
+				"default": msgs,
+			},
+			qnames:           []string{"default"},
+			queueConcurrency: map[string]int{"default": 0},
+			wantMsgs:         msgs,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			h.FlushDB(t, r.client) // clean up db before each test case
+			h.SeedAllPendingQueues(t, r.client, tc.pending)
+
+			r.queueConcurrency = tc.queueConcurrency
+			gotMsgs := make([]*base.TaskMessage, 0, len(msgs))
+			for i := 0; i < len(msgs); i++ {
+				msg, _, err := r.Dequeue(tc.qnames...)
+				if errors.Is(err, errors.ErrNoProcessableTask) {
+					break
+				}
+				if err != nil {
+					t.Errorf("(*RDB).Dequeue(%v) returned error %v", tc.qnames, err)
+					continue
+				}
+				gotMsgs = append(gotMsgs, msg)
+			}
+			if diff := cmp.Diff(tc.wantMsgs, gotMsgs, h.SortZSetEntryOpt); diff != "" {
+				t.Errorf("(*RDB).Dequeue(%v) returned message %v; want %v",
+					tc.qnames, gotMsgs, tc.wantMsgs)
+			}
+		})
+	}
+}
+
 func TestDequeueError(t *testing.T) {
 	r := setup(t)
 	defer r.Close()

server.go

@@ -103,7 +103,7 @@ type Config struct {
 	// If BaseContext is nil, the default is context.Background().
 	// If this is defined, then it MUST return a non-nil context
 	BaseContext func() context.Context
-	
+
 	// TaskCheckInterval specifies the interval between checks for new tasks to process when all queues are empty.
 	//
 	// If unset, zero or a negative value, the interval is set to 1 second.
@@ -239,6 +239,11 @@ type Config struct {
 	//
 	// If unset or nil, the group aggregation feature will be disabled on the server.
 	GroupAggregator GroupAggregator
+
+	// Maximum number of concurrent tasks of a queue.
+	//
+	// If set to a zero or not set, NewServer will not limit concurrency of the queue.
+	QueueConcurrency map[string]int
 }
 
 // GroupAggregator aggregates a group of tasks into one before the tasks are passed to the Handler.
@@ -478,7 +483,7 @@ func NewServer(r RedisConnOpt, cfg Config) *Server {
 	}
 	logger.SetLevel(toInternalLogLevel(loglevel))
 
-	rdb := rdb.NewRDB(c)
+	rdb := rdb.NewRDB(c, rdb.WithQueueConcurrency(cfg.QueueConcurrency))
 	starting := make(chan *workerInfo)
 	finished := make(chan *base.TaskMessage)
 	syncCh := make(chan *syncRequest)

server_test.go

@@ -7,6 +7,7 @@ package asynq
 import (
 	"context"
 	"fmt"
+	"github.com/redis/go-redis/v9"
 	"syscall"
 	"testing"
 	"time"
@@ -53,6 +54,99 @@ func TestServer(t *testing.T) {
 	srv.Shutdown()
 }
 
+func TestServerWithQueueConcurrency(t *testing.T) {
+	// https://github.com/go-redis/redis/issues/1029
+	ignoreOpt := goleak.IgnoreTopFunction("github.com/redis/go-redis/v9/internal/pool.(*ConnPool).reaper")
+	defer goleak.VerifyNone(t, ignoreOpt)
+
+	redisConnOpt := getRedisConnOpt(t)
+	r, ok := redisConnOpt.MakeRedisClient().(redis.UniversalClient)
+	if !ok {
+		t.Fatalf("asynq: unsupported RedisConnOpt type %T", r)
+	}
+
+	c := NewClient(redisConnOpt)
+	defer c.Close()
+
+	const taskNum = 8
+	const serverNum = 2
+	tests := []struct {
+		name             string
+		concurrency      int
+		queueConcurrency int
+		wantActiveNum    int
+	}{
+		{
+			name:             "based on client concurrency control",
+			concurrency:      2,
+			queueConcurrency: 6,
+			wantActiveNum:    2 * serverNum,
+		},
+		{
+			name:             "no queue concurrency control",
+			concurrency:      2,
+			queueConcurrency: 0,
+			wantActiveNum:    2 * serverNum,
+		},
+		{
+			name:             "based on queue concurrency control",
+			concurrency:      6,
+			queueConcurrency: 2,
+			wantActiveNum:    2,
+		},
+	}
+
+	// no-op handler
+	handle := func(ctx context.Context, task *Task) error {
+		time.Sleep(time.Second * 2)
+		return nil
+	}
+
+	const queueName = "default"
+	var servers [serverNum]*Server
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var err error
+			testutil.FlushDB(t, r)
+			for i := 0; i < taskNum; i++ {
+				_, err = c.Enqueue(NewTask("send_email",
+					testutil.JSON(map[string]interface{}{"recipient_id": i + 123})))
+				if err != nil {
+					t.Fatalf("could not enqueue a task: %v", err)
+				}
+			}
+
+			for i := 0; i < serverNum; i++ {
+				srv := NewServer(redisConnOpt, Config{
+					Concurrency:      tc.concurrency,
+					LogLevel:         testLogLevel,
+					QueueConcurrency: map[string]int{queueName: tc.queueConcurrency},
+				})
+				err = srv.Start(HandlerFunc(handle))
+				if err != nil {
+					t.Fatal(err)
+				}
+				servers[i] = srv
+			}
+			defer func() {
+				for _, srv := range servers {
+					srv.Shutdown()
+				}
+			}()
+
+			time.Sleep(time.Second)
+			inspector := NewInspector(redisConnOpt)
+			tasks, err := inspector.ListActiveTasks(queueName)
+			if err != nil {
+				t.Fatalf("could not list active tasks: %v", err)
+			}
+			if len(tasks) != tc.wantActiveNum {
+				t.Errorf("default queue has %d active tasks, want %d", len(tasks), tc.wantActiveNum)
+			}
+		})
+	}
+}
+
 func TestServerRun(t *testing.T) {
 	// https://github.com/go-redis/redis/issues/1029
 	ignoreOpt := goleak.IgnoreTopFunction("github.com/redis/go-redis/v9/internal/pool.(*ConnPool).reaper")