From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
Subject: [PATCH] daed: serialize scheduled subscription updates
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订阅更新的入口读也纳入同一把锁，整轮更新串行，排到才开始计时。

多个订阅定时任务撞在同一分钟时会互相锁死。
---
 .../service/subscription/mutation_utils.go    | 29 +++++++++++++------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/graphql/service/subscription/mutation_utils.go b/graphql/service/subscription/mutation_utils.go
index c6bc3e1..e2aec32 100644
--- a/graphql/service/subscription/mutation_utils.go
+++ b/graphql/service/subscription/mutation_utils.go
@@ -225,12 +225,8 @@ func AddUpdateScheduler(ctx context.Context, id uint) {
 		tag = *sub.Tag
 	}
 	logrus.Info("Subscription " + tag + " update task enabled, with exp " + sub.CronExp)
-	_, err := s.Cron(sub.CronExp).Do(func() {
-		ctx, cancel := context.WithTimeout(context.Background(), scheduledUpdateTimeout)
-		defer cancel()
-		if _, err := UpdateById(ctx, sub.ID); err != nil {
-			logrus.Error(err)
-		}
+	_, err := s.Cron(sub.CronExp).SingletonMode().Do(func() {
+		runScheduledUpdate(sub.ID)
 	})
 	if err != nil {
 		logrus.Errorf("Failed to schedule subscription %d update: invalid cron expression '%s': %v", sub.ID, sub.CronExp, err)
@@ -364,9 +360,6 @@ func reconcileSubscriptionNodes(tx *gorm.DB, subId uint, links []string) error {
 }
 
 func updateSubscriptionTx(ctx context.Context, m *db.Subscription, subId uint, links []string) (err error) {
-	subscriptionUpdateMu.Lock()
-	defer subscriptionUpdateMu.Unlock()
-
 	tx := db.BeginTx(ctx)
 	if tx.Error != nil {
 		return tx.Error
@@ -404,7 +397,25 @@ func updateSubscriptionTx(ctx context.Context, m *db.Subscription, subId uint, l
 	return tx.Commit().Error
 }
 
+func runScheduledUpdate(subId uint) {
+	subscriptionUpdateMu.Lock()
+	defer subscriptionUpdateMu.Unlock()
+
+	ctx, cancel := context.WithTimeout(context.Background(), scheduledUpdateTimeout)
+	defer cancel()
+	if _, err := updateByIdLocked(ctx, subId); err != nil {
+		logrus.Error(err)
+	}
+}
+
 func UpdateById(ctx context.Context, subId uint) (sub *db.Subscription, err error) {
+	subscriptionUpdateMu.Lock()
+	defer subscriptionUpdateMu.Unlock()
+
+	return updateByIdLocked(ctx, subId)
+}
+
+func updateByIdLocked(ctx context.Context, subId uint) (sub *db.Subscription, err error) {
 	var m db.Subscription
 	if err = db.DB(ctx).Where(&db.Subscription{ID: subId}).First(&m).Error; err != nil {
 		return nil, err