use sync.Once to lazy load cache

internal/service/interest.go

@@ -11,21 +11,13 @@ import (
 )
 
 type interestCache struct {
-	sync.Mutex
-	loaded   bool
+	sync.Once
 	postings map[time.Time][]posting.Posting
 }
 
 var icache interestCache
 
 func loadInterestCache(db *gorm.DB) {
-	icache.Lock()
-	defer icache.Unlock()
-
-	if icache.loaded {
-		return
-	}
-
 	var postings []posting.Posting
 	result := db.Where("account like ?", "Income:Interest:%").Find(&postings)
 	if result.Error != nil {
@@ -33,16 +25,15 @@ func loadInterestCache(db *gorm.DB) {
 	}
 
 	icache.postings = lo.GroupBy(postings, func(p posting.Posting) time.Time { return p.Date })
-	icache.loaded = true
 }
 
 func IsInterest(db *gorm.DB, p posting.Posting) bool {
+	icache.Do(func() { loadInterestCache(db) })
+
 	if p.Commodity != "INR" {
 		return false
 	}
 
-	loadInterestCache(db)
-
 	for _, ip := range icache.postings[p.Date] {
 		if ip.Date.Equal(p.Date) &&
 			-ip.Amount == p.Amount &&

internal/service/market.go

@@ -14,21 +14,13 @@ import (
 )
 
 type priceCache struct {
-	sync.Mutex
-	loaded     bool
+	sync.Once
 	pricesTree map[string]*btree.BTree
 }
 
 var pcache priceCache
 
 func loadPriceCache(db *gorm.DB) {
-	pcache.Lock()
-	defer pcache.Unlock()
-
-	if pcache.loaded {
-		return
-	}
-
 	var prices []price.Price
 	result := db.Find(&prices)
 	if result.Error != nil {
@@ -58,12 +50,11 @@ func loadPriceCache(db *gorm.DB) {
 			}
 		}
 	}
-
-	pcache.loaded = true
 }
 
 func GetMarketPrice(db *gorm.DB, p posting.Posting, date time.Time) float64 {
-	loadPriceCache(db)
+	pcache.Do(func() { loadPriceCache(db) })
+
 	if p.Commodity == "INR" {
 		return p.Amount
 	}