Acquire a new connection for every queue listener (#38)

.github/workflows/goreleaser.yml

@@ -20,7 +20,7 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           WITH_V: true
-          DEFAULT_BUMP: patch
+          DEFAULT_BUMP: minor
       -
         name: Set up Go
         uses: actions/setup-go@v3

Makefile

@@ -58,7 +58,7 @@ test-watch:
 .PHONY: lint
 lint:
 	@clear
-	@golangci-lint run .
+	@golangci-lint run
 
 .PHONY: lint-watch
 lint-watch: install-reflex

backends/memory/memory_backend.go

@@ -86,7 +86,7 @@ func (m *MemBackend) Enqueue(ctx context.Context, job *jobs.Job) (jobID int64, e
 	}
 
 	if job.Queue == "" {
-		err = errors.New("this job does not specify a Queue. Please specify a queue")
+		err = jobs.ErrNoQueueSpecified
 
 		return
 	}
@@ -264,7 +264,7 @@ func (m *MemBackend) scheduleFutureJobs(ctx context.Context, queue string) {
 						queueChan = qc.(chan *jobs.Job)
 						queueChan <- j
 					} else {
-						m.logger.Error(fmt.Sprintf("no queue processor for queue '%s'", queue), errors.New("no queue processor configured"))
+						m.logger.Error(fmt.Sprintf("no queue processor for queue '%s'", queue), handler.ErrNoHandlerForQueue)
 					}
 				}(job)
 			}

backends/memory/memory_backend_test.go

@@ -193,7 +193,7 @@ func TestFutureJobScheduling(t *testing.T) {
 }
 
 func TestCron(t *testing.T) {
-	const cron = "* * * * * *"
+	const cronSpec = "* * * * * *"
 	ctx := context.TODO()
 	nq, err := neoq.New(ctx, neoq.WithBackend(memory.Backend))
 	if err != nil {
@@ -212,7 +212,7 @@ func TestCron(t *testing.T) {
 		handler.Concurrency(1),
 	)
 
-	err = nq.StartCron(ctx, cron, h)
+	err = nq.StartCron(ctx, cronSpec, h)
 	if err != nil {
 		t.Error(err)
 	}

backends/postgres/postgres_backend.go

@@ -54,11 +54,12 @@ const (
 type contextKey struct{}
 
 var (
-	txCtxVarKey               contextKey
-	ErrCnxString              = errors.New("invalid connecton string: see documentation for valid connection strings")
-	ErrDuplicateJobID         = errors.New("duplicate job id")
-	ErrNoQueue                = errors.New("no queue specified")
-	ErrNoTransactionInContext = errors.New("context does not have a Tx set")
+	txCtxVarKey                   contextKey
+	shutdownJobID                 int64 = -1  // job ID announced when triggering a shutdown
+	shutdownAnnouncementAllowance       = 100 // ms
+	ErrCnxString                        = errors.New("invalid connecton string: see documentation for valid connection strings")
+	ErrDuplicateJobID                   = errors.New("duplicate job id")
+	ErrNoTransactionInContext           = errors.New("context does not have a Tx set")
 )
 
 // PgBackend is a Postgres-based Neoq backend
@@ -67,7 +68,6 @@ type PgBackend struct {
 	config      *config.Config
 	logger      logging.Logger
 	cron        *cron.Cron
-	listenConn  *pgx.Conn
 	mu          *sync.Mutex // mutex to protect mutating state on a pgWorker
 	pool        *pgxpool.Pool
 	futureJobs  map[int64]time.Time        // map of future job IDs to their due time
@@ -155,7 +155,7 @@ func Backend(ctx context.Context, opts ...config.Option) (pb types.Backend, err
 
 	pb = p
 
-	return
+	return pb, nil
 }
 
 // WithTransactionTimeout sets the time that PgBackend's transactions may be idle before its underlying connection is
@@ -344,7 +344,7 @@ func (p *PgBackend) Enqueue(ctx context.Context, job *jobs.Job) (jobID int64, er
 	}
 
 	if job.Queue == "" {
-		err = ErrNoQueue
+		err = jobs.ErrNoQueueSpecified
 		return
 	}
 
@@ -418,15 +418,17 @@ func (p *PgBackend) StartCron(ctx context.Context, cronSpec string, h handler.Ha
 	if err = p.cron.AddFunc(cronSpec, func() {
 		_, err := p.Enqueue(ctx, &jobs.Job{Queue: queue})
 		if err != nil {
+			if errors.Is(err, context.Canceled) {
+				return
+			}
+
 			p.logger.Error("error queueing cron job", err)
 		}
 	}); err != nil {
 		return fmt.Errorf("error adding cron: %w", err)
 	}
 
-	err = p.Start(ctx, queue, h)
-
-	return
+	return p.Start(ctx, queue, h)
 }
 
 // SetLogger sets this backend's logger
@@ -435,13 +437,20 @@ func (p *PgBackend) SetLogger(logger logging.Logger) {
 }
 
 func (p *PgBackend) Shutdown(ctx context.Context) {
-	p.pool.Close() // also closes the hijacked listenConn
-	p.cron.Stop()
+	for queue := range p.handlers {
+		p.announceJob(ctx, queue, shutdownJobID)
+	}
+
+	// wait for the announcement to process
+	time.Sleep(time.Duration(shutdownAnnouncementAllowance) * time.Millisecond)
 
 	for _, f := range p.cancelFuncs {
 		f()
 	}
 
+	p.pool.Close()
+	p.cron.Stop()
+
 	p.cancelFuncs = nil
 }
 
@@ -560,26 +569,11 @@ func (p *PgBackend) start(ctx context.Context, queue string) (err error) {
 	if h, ok = p.handlers[queue]; !ok {
 		return fmt.Errorf("%w: %s", handler.ErrNoHandlerForQueue, queue)
 	}
-	conn, err := p.pool.Acquire(ctx)
-	if err != nil {
-		return
-	}
-
-	// use a single connection to listen for jobs on all queues
-	// TODO: Give more thought to the implications of hijacking connections to LISTEN on in PgBackend
-	// should this connecton not come from the pool, to avoid tainting it with connections that don't have an idle in
-	// transaction time out set?
-	p.mu.Lock()
-	if p.listenConn == nil {
-		p.listenConn = conn.Hijack()
-	}
-	p.mu.Unlock()
 
 	listenJobChan := p.listen(ctx, queue)        // listen for 'new' jobs
 	pendingJobsChan := p.pendingJobs(ctx, queue) // process overdue jobs *at startup*
 
 	// process all future jobs and retries
-	// TODO consider performance implications of `scheduleFutureJobs` in PgBackend
 	go func() { p.scheduleFutureJobs(ctx, queue) }()
 
 	for i := 0; i < h.Concurrency; i++ {
@@ -598,7 +592,7 @@ func (p *PgBackend) start(ctx context.Context, queue string) (err error) {
 				}
 
 				if err != nil {
-					if errors.Is(err, pgx.ErrNoRows) {
+					if errors.Is(err, pgx.ErrNoRows) || errors.Is(err, context.Canceled) {
 						err = nil
 						continue
 					}
@@ -625,26 +619,31 @@ func (p *PgBackend) removeFutureJob(jobID int64) {
 
 // initFutureJobs is intended to be run once to initialize the list of future jobs that must be monitored for
 // execution. it should be run only during system startup.
-func (p *PgBackend) initFutureJobs(ctx context.Context, queue string) {
+func (p *PgBackend) initFutureJobs(ctx context.Context, queue string) (err error) {
 	rows, err := p.pool.Query(ctx, FutureJobQuery, queue)
 	if err != nil {
-		p.logger.Error("error fetching future jobs list", err)
+		p.logger.Error("failed to fetch future jobs list", err)
 		return
 	}
 
 	var id int64
 	var runAfter time.Time
-	_, _ = pgx.ForEachRow(rows, []any{&id, &runAfter}, func() error {
+	_, err = pgx.ForEachRow(rows, []any{&id, &runAfter}, func() error {
 		p.mu.Lock()
 		p.futureJobs[id] = runAfter
 		p.mu.Unlock()
 		return nil
 	})
+
+	return
 }
 
 // scheduleFutureJobs announces future jobs using NOTIFY on an interval
 func (p *PgBackend) scheduleFutureJobs(ctx context.Context, queue string) {
-	p.initFutureJobs(ctx, queue)
+	err := p.initFutureJobs(ctx, queue)
+	if err != nil {
+		return
+	}
 
 	// check for new future jobs on an interval
 	ticker := time.NewTicker(p.config.JobCheckInterval)
@@ -718,12 +717,11 @@ func (p *PgBackend) pendingJobs(ctx context.Context, queue string) (jobsCh chan
 		for {
 			jobID, err := p.getPendingJobID(ctx, conn, queue)
 			if err != nil {
-				if !errors.Is(err, pgx.ErrNoRows) {
-					p.logger.Error("failed to fetch pending job", err, "job_id", jobID)
-				} else {
-					// done fetching pending jobs
+				if errors.Is(err, pgx.ErrNoRows) || errors.Is(err, context.Canceled) {
 					break
 				}
+
+				p.logger.Error("failed to fetch pending job", err, "job_id", jobID)
 			} else {
 				jobsCh <- jobID
 			}
@@ -774,6 +772,10 @@ func (p *PgBackend) handleJob(ctx context.Context, jobID int64, h handler.Handle
 
 	err = p.updateJob(ctx, jobErr)
 	if err != nil {
+		if errors.Is(err, context.Canceled) {
+			return
+		}
+
 		err = fmt.Errorf("error updating job status: %w", err)
 		return err
 	}
@@ -792,43 +794,74 @@ func (p *PgBackend) handleJob(ctx context.Context, jobID int64, h handler.Handle
 // This will lead to jobs not getting processed until the worker is restarted.
 // Implement disconnect handling.
 func (p *PgBackend) listen(ctx context.Context, queue string) (c chan int64) {
-	var err error
 	c = make(chan int64)
 
-	// set this connection's idle in transaction timeout to infinite so it is not intermittently disconnected
-	_, err = p.listenConn.Exec(ctx, fmt.Sprintf("SET idle_in_transaction_session_timeout = '0'; LISTEN %s", queue))
-	if err != nil {
-		err = fmt.Errorf("unable to create database connection for listener: %w", err)
-		p.logger.Error("unablet o create database connection for listener", err)
-		return
-	}
-
 	go func(ctx context.Context) {
 		for {
-			notification, waitErr := p.listenConn.WaitForNotification(ctx)
+			conn, err := p.pool.Acquire(ctx)
+			if err != nil {
+				p.logger.Error("unable to acquire new connnection", err)
+				return
+			}
+
+			// set this connection's idle in transaction timeout to infinite so it is not intermittently disconnected
+			_, err = conn.Exec(ctx, fmt.Sprintf("SET idle_in_transaction_session_timeout = '0'; LISTEN %s", queue))
+			if err != nil {
+				err = fmt.Errorf("unable to configure listener connection: %w", err)
+				p.logger.Error("unable to configure listener connection", err)
+				time.Sleep(time.Second) // don't hammer the db
+				p.release(ctx, conn, queue)
+				continue
+			}
+
+			notification, waitErr := conn.Conn().WaitForNotification(ctx)
 			if waitErr != nil {
 				if errors.Is(waitErr, context.Canceled) {
+					p.release(ctx, conn, queue)
 					return
 				}
 
 				p.logger.Error("failed to wait for notification", waitErr)
-				time.Sleep(1 * time.Second)
+				p.release(ctx, conn, queue)
 				continue
 			}
 
 			var jobID int64
 			if jobID, err = strconv.ParseInt(notification.Payload, 0, 64); err != nil {
 				p.logger.Error("unable to fetch job", err)
+				p.release(ctx, conn, queue)
 				continue
 			}
 
+			// check if Shutdown() has been called
+			if jobID == shutdownJobID {
+				p.release(ctx, conn, queue)
+				return
+			}
+
 			c <- jobID
+
+			p.release(ctx, conn, queue)
 		}
 	}(ctx)
 
 	return c
 }
 
+func (p *PgBackend) release(ctx context.Context, conn *pgxpool.Conn, queue string) {
+	query := fmt.Sprintf("SET idle_in_transaction_session_timeout = '%d'; UNLISTEN %s", p.config.IdleTransactionTimeout, queue)
+	_, err := conn.Exec(ctx, query)
+	if err != nil {
+		if errors.Is(err, context.Canceled) {
+			return
+		}
+
+		p.logger.Error("unable to reset connection config before release", err)
+	}
+
+	conn.Release()
+}
+
 func (p *PgBackend) getPendingJob(ctx context.Context, tx pgx.Tx, jobID int64) (job *jobs.Job, err error) {
 	row, err := tx.Query(ctx, PendingJobQuery, jobID)
 	if err != nil {