// Copyright 2017 The Gitea Authors. All rights reserved.// SPDX-License-Identifier: MIT package cache import (	"errors"	"fmt"	"strconv"	"time" 	"forgejo.org/modules/log"	"forgejo.org/modules/setting" 	mc "code.forgejo.org/go-chi/cache" 	_ "code.forgejo.org/go-chi/cache/memcache" // memcache plugin for cache) var (	conn             mc.Cache	ErrInconvertible = errors.New("value from cache was not convertible to expected type")	mutexMap         MutexMap) func newCache(cacheConfig setting.Cache) (mc.Cache, error) {	return mc.NewCacher(mc.Options{		Adapter:       cacheConfig.Adapter,		AdapterConfig: cacheConfig.Conn,		Interval:      cacheConfig.Interval,	})} // Init start cache servicefunc Init() error {	var err error 	if conn == nil {		if conn, err = newCache(setting.CacheService.Cache); err != nil {			return err		}		if err = conn.Ping(); err != nil {			return err		}	} 	return err} const (	testCacheKey       = "DefaultCache.TestKey"	SlowCacheThreshold = 100 * time.Microsecond) func Test() (time.Duration, error) {	if conn == nil {		return 0, errors.New("default cache not initialized")	} 	testData := fmt.Sprintf("%x", make([]byte, 500)) 	start := time.Now() 	if err := conn.Delete(testCacheKey); err != nil {		return 0, fmt.Errorf("expect cache to delete data based on key if exist but got: %w", err)	}	if err := conn.Put(testCacheKey, testData, 10); err != nil {		return 0, fmt.Errorf("expect cache to store data but got: %w", err)	}	testVal := conn.Get(testCacheKey)	if testVal == nil {		return 0, errors.New("expect cache hit but got none")	}	if testVal != testData {		return 0, errors.New("expect cache to return same value as stored but got other")	} 	return time.Since(start), nil} // GetCache returns the currently configured cachefunc GetCache() mc.Cache {	return conn} // concurrencySafeGet is a single-process concurrency safe fetch from the cache, which provides the guarantee that after// calling `cache.Remove(key)` and then `cache.Get*(key, ...)`, the value returned from cache will never have been// computed **before** the `Remove` invocation.  It uses in-memory synchronization, so its guarantee does not extend to// a clustered configuration.//// getFunc is the computation for the value if caching is not available.  convertFunc converts the cached value into the// target type, and can return `ErrInconvertible` to indicate that the value couldn't be converts and should be// recomputed instead; other errors are passed through.func concurrencySafeGet[T any](key string, getFunc func() (T, error), convertFunc func(v any) (T, error)) (T, error) {	if conn == nil || setting.CacheService.TTL <= 0 {		return getFunc()	} 	// Use a double-checking method -- once before acquiring the write lock on this key (this block), and then again	// afterwards to avoid calling `getFunc` if it was computed while we were acquiring the lock. This causes two cache	// hits as a trade-off to minimize the number of lock acquisitions. If this trade-off causes too much cache load,	// this first `Get` could be removed -- the second one is performance-critical to ensure that after waiting a "long	// time" to compute w/ `getFunc`, we don't immediately redo that work after acquiring the lock.	cached := conn.Get(key)	if cached != nil {		retval, err := convertFunc(cached)		if err == nil {			return retval, nil		} else if !errors.Is(err, ErrInconvertible) { // for ErrInconvertible we'll fall through to recalculating the value			var zero T			return zero, err		}	} 	defer mutexMap.Lock(key)() 	// The second, performance-critical, check if the cache contains the target value.	cached = conn.Get(key)	if cached != nil {		retval, err := convertFunc(cached)		if err == nil {			return retval, nil		} else if !errors.Is(err, ErrInconvertible) { // for ErrInconvertible we'll fall through to recalculating the value			var zero T			return zero, err		}	} 	value, err := getFunc()	if err != nil {		return value, err	}	return value, conn.Put(key, value, setting.CacheService.TTLSeconds())} // GetString returns the key value from cache with callback when no key exists in cachefunc GetString(key string, getFunc func() (string, error)) (string, error) {	v, err := concurrencySafeGet(key, getFunc, func(cached any) (string, error) {		if value, ok := cached.(string); ok {			return value, nil		}		if stringer, ok := cached.(fmt.Stringer); ok {			return stringer.String(), nil		}		return fmt.Sprintf("%s", cached), nil	})	return v, err} // GetInt returns key value from cache with callback when no key exists in cachefunc GetInt(key string, getFunc func() (int, error)) (int, error) {	v, err := concurrencySafeGet(key, getFunc, func(cached any) (int, error) {		switch v := cached.(type) {		case int:			return v, nil		case string:			value, err := strconv.Atoi(v)			if err != nil {				return 0, err			}			return value, nil		}		return 0, ErrInconvertible	})	return v, err} // GetInt64 returns key value from cache with callback when no key exists in cachefunc GetInt64(key string, getFunc func() (int64, error)) (int64, error) {	v, err := concurrencySafeGet(key, getFunc, func(cached any) (int64, error) {		switch v := cached.(type) {		case int64:			return v, nil		case string:			value, err := strconv.ParseInt(v, 10, 64)			if err != nil {				return 0, err			}			return value, nil		}		return 0, ErrInconvertible	})	return v, err} // Remove key from cachefunc Remove(key string) {	if conn == nil {		return	} 	// The goal of `Remove(key)` is to ensure that *after* it is completed, a new value is computed.  It's possible that	// a value is being computed for the key *right now* -- `getFunc` is about to return, we're about to delete the key,	// and then it will be Put into the cache with an out-of-date value computed before the `Remove(key)`. To prevent	// this we need the `Remove(key)` to also lock on the key, just like `Get*(key, ...)` does when computing it.	defer mutexMap.Lock(key)() 	err := conn.Delete(key)	if err != nil {		log.Error("unexpected error deleting key %s from cache: %v", err)	}}