shekhar/windows-iso-downloader
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fix: route background stale refresh through singleflight; cleanup logging

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- Background refresh on stale serve now goes through sfGroup.Do so
  concurrent stale hits collapse into one Microsoft call instead of
  hammering the API from multiple goroutines simultaneously.

- cleanupCaches: only logs when entries are actually evicted (was
  logging every 30min regardless of whether anything changed).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Shekhar Vaidya 2026-05-18 23:12:59 +05:30
parent a0a6341d5f
commit 90c498233b
1 changed files with 22 additions and 11 deletions
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33
backend/main.go
View file

@ -829,16 +829,21 @@ func handleProxy(w http.ResponseWriter, r *http.Request) {
atomic.AddInt64(&mLinkStale, 1)
log.Printf("/proxy: product_id=%s sku_id=%s -> fetch failed (%v), serving stale\n", productID, skuID, err)
go func() {
raw, bgErr := fetchDownloadLinksFromMS(productID, skuID)
if bgErr != nil {
log.Printf("/proxy: background refresh failed for %s:%s: %v\n", productID, skuID, bgErr)
return
}
exp := parseLinkExpiry(raw)
linkCacheMu.Lock()
linkCache[cacheKey] = linkCacheEntry{RawJSON: raw, ExpiresAt: exp, FetchedAt: time.Now()}
linkCacheMu.Unlock()
log.Printf("/proxy: background refresh succeeded for %s:%s, cached until %s\n", productID, skuID, exp.Format(time.RFC3339))
// Use singleflight so concurrent stale serves don't all hit Microsoft
sfBgKey := "link:" + cacheKey
sfGroup.Do(sfBgKey, func() (interface{}, error) {
raw, bgErr := fetchDownloadLinksFromMS(productID, skuID)
if bgErr != nil {
log.Printf("/proxy: background refresh failed for %s:%s: %v\n", productID, skuID, bgErr)
return nil, bgErr
}
exp := parseLinkExpiry(raw)
linkCacheMu.Lock()
linkCache[cacheKey] = linkCacheEntry{RawJSON: raw, ExpiresAt: exp, FetchedAt: time.Now()}
linkCacheMu.Unlock()
log.Printf("/proxy: background refresh succeeded for %s:%s, cached until %s\n", productID, skuID, exp.Format(time.RFC3339))
return nil, nil
})
}()
w.Write(cached.RawJSON)
return
@ -943,11 +948,13 @@ func cleanupCaches() {
ticker := time.NewTicker(30 * time.Minute)
for range ticker.C {
now := time.Now()
var skuDel, linkDel, negDel int
skuCacheMu.Lock()
for k, v := range skuCache {
if now.After(v.ExpiresAt) {
delete(skuCache, k)
skuDel++
}
}
skuCacheMu.Unlock()
@ -957,6 +964,7 @@ func cleanupCaches() {
for k, v := range linkCache {
if now.After(v.ExpiresAt.Add(4 * time.Hour)) {
delete(linkCache, k)
linkDel++
}
}
linkCacheMu.Unlock()
@ -965,11 +973,14 @@ func cleanupCaches() {
for k, v := range negCache {
if now.After(v.ExpiresAt) {
delete(negCache, k)
negDel++
}
}
negCacheMu.Unlock()
log.Printf("cache cleanup: sku=%d link=%d neg=%d\n", len(skuCache), len(linkCache), len(negCache))
if skuDel+linkDel+negDel > 0 {
log.Printf("cache cleanup: evicted sku=%d link=%d neg=%d\n", skuDel, linkDel, negDel)
}
}
}