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// Copyright 2022 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package cache
import (
"context"
"sync"
"time"
"code.gitea.io/gitea/modules/log"
)
// cacheContext is a context that can be used to cache data in a request level context
// This is useful for caching data that is expensive to calculate and is likely to be
// used multiple times in a request.
type cacheContext struct {
data map[any]map[any]any
lock sync.RWMutex
created time.Time
discard bool
}
func (cc *cacheContext) Get(tp, key any) any {
cc.lock.RLock()
defer cc.lock.RUnlock()
return cc.data[tp][key]
}
func (cc *cacheContext) Put(tp, key, value any) {
cc.lock.Lock()
defer cc.lock.Unlock()
if cc.discard {
return
}
d := cc.data[tp]
if d == nil {
d = make(map[any]any)
cc.data[tp] = d
}
d[key] = value
}
func (cc *cacheContext) Delete(tp, key any) {
cc.lock.Lock()
defer cc.lock.Unlock()
delete(cc.data[tp], key)
}
func (cc *cacheContext) Discard() {
cc.lock.Lock()
defer cc.lock.Unlock()
cc.data = nil
cc.discard = true
}
func (cc *cacheContext) isDiscard() bool {
cc.lock.RLock()
defer cc.lock.RUnlock()
return cc.discard
}
// cacheContextLifetime is the max lifetime of cacheContext.
// Since cacheContext is used to cache data in a request level context, 5 minutes is enough.
// If a cacheContext is used more than 5 minutes, it's probably misuse.
const cacheContextLifetime = 5 * time.Minute
var timeNow = time.Now
func (cc *cacheContext) Expired() bool {
return timeNow().Sub(cc.created) > cacheContextLifetime
}
type cacheContextType = struct{ useless struct{} }
var cacheContextKey = cacheContextType{useless: struct{}{}}
/*
Since there are both WithCacheContext and WithNoCacheContext,
it may be confusing when there is nesting.
Some cases to explain the design:
When:
- A, B or C means a cache context.
- A', B' or C' means a discard cache context.
- ctx means context.Backgrand().
- A(ctx) means a cache context with ctx as the parent context.
- B(A(ctx)) means a cache context with A(ctx) as the parent context.
- With is alias of WithCacheContext.
- WithNo is alias of WithNoCacheContext.
So:
- With(ctx) -> A(ctx)
- With(With(ctx)) -> A(ctx), not B(A(ctx)), always reuse parent cache context if possible.
- With(With(With(ctx))) -> A(ctx), not C(B(A(ctx))), ditto.
- WithNo(ctx) -> ctx, not A'(ctx), don't create new cache context if we don't have to.
- WithNo(With(ctx)) -> A'(ctx)
- WithNo(WithNo(With(ctx))) -> A'(ctx), not B'(A'(ctx)), don't create new cache context if we don't have to.
- With(WithNo(With(ctx))) -> B(A'(ctx)), not A(ctx), never reuse a discard cache context.
- WithNo(With(WithNo(With(ctx)))) -> B'(A'(ctx))
- With(WithNo(With(WithNo(With(ctx))))) -> C(B'(A'(ctx))), so there's always only one not-discard cache context.
*/
func WithCacheContext(ctx context.Context) context.Context {
if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
if !c.isDiscard() {
// reuse parent context
return ctx
}
}
return context.WithValue(ctx, cacheContextKey, &cacheContext{
data: make(map[any]map[any]any),
created: timeNow(),
})
}
func WithNoCacheContext(ctx context.Context) context.Context {
if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
// The caller want to run long-life tasks, but the parent context is a cache context.
// So we should disable and clean the cache data, or it will be kept in memory for a long time.
c.Discard()
return ctx
}
return ctx
}
func GetContextData(ctx context.Context, tp, key any) any {
if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
if c.Expired() {
// The warning means that the cache context is misused for long-life task,
// it can be resolved with WithNoCacheContext(ctx).
log.Warn("cache context is expired, is highly likely to be misused for long-life tasks: %v", c)
return nil
}
return c.Get(tp, key)
}
return nil
}
func SetContextData(ctx context.Context, tp, key, value any) {
if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
if c.Expired() {
// The warning means that the cache context is misused for long-life task,
// it can be resolved with WithNoCacheContext(ctx).
log.Warn("cache context is expired, is highly likely to be misused for long-life tasks: %v", c)
return
}
c.Put(tp, key, value)
return
}
}
func RemoveContextData(ctx context.Context, tp, key any) {
if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
if c.Expired() {
// The warning means that the cache context is misused for long-life task,
// it can be resolved with WithNoCacheContext(ctx).
log.Warn("cache context is expired, is highly likely to be misused for long-life tasks: %v", c)
return
}
c.Delete(tp, key)
}
}
// GetWithContextCache returns the cache value of the given key in the given context.
func GetWithContextCache[T any](ctx context.Context, cacheGroupKey string, cacheTargetID any, f func() (T, error)) (T, error) {
v := GetContextData(ctx, cacheGroupKey, cacheTargetID)
if vv, ok := v.(T); ok {
return vv, nil
}
t, err := f()
if err != nil {
return t, err
}
SetContextData(ctx, cacheGroupKey, cacheTargetID, t)
return t, nil
}
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