Method internAt

internal/decoder/string_cache.go:36–70

internAt returns a string for the data at the given offset and size. Hot offsets are interned and the same backing string is returned on subsequent hits; cold offsets are returned freshly allocated on every call (see the admission rule below).

(offset, size uint, data []byte)

// subsequent hits; cold offsets are returned freshly allocated on every
// call (see the admission rule below).
func (sc *stringCache) internAt(offset, size uint, data []byte) string {
	const (
		minCachedLen = 2   // single byte strings not worth caching
		maxCachedLen = 100 // reasonable upper bound for geographic strings
	)

	if size < minCachedLen || size > maxCachedLen {
		return string(data[offset : offset+size])
	}

	i := offset % uint(len(sc.entries))
	entry := &sc.entries[i]

	if cached := entry.Load(); cached != nil && cached.offset == offset {
		return cached.str
	}

	str := string(data[offset : offset+size])

	// Only admit strings that miss twice in the same slot. This keeps the
	// lock-free fast path for hot strings while avoiding heap churn for one-offs.
	// The +1 bias reserves 0 as the "no prior miss" sentinel so the initial
	// zero state of recentMisses[i] never spuriously matches a real offset of 0.
	admissionValue := uint64(offset) + 1
	if sc.recentMisses[i].Load() == admissionValue {
		entry.Store(&cacheEntry{
			str:    str,
			offset: offset,
		})
	} else {
		sc.recentMisses[i].Store(admissionValue)
	}

	return str
}