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Related to: #22294 #23186 #23054 Replace: #23218 Some discussion is in the comments of #23218. Highlights: - Add Expiration for cache context. If a cache context has been used for more than 10s, the cache data will be ignored, and warning logs will be printed. - Add `discard` field to `cacheContext`, a `cacheContext` with `discard` true will drop all cached data and won't store any new one. - Introduce `WithNoCacheContext`, if one wants to run long-life tasks, but the parent context is a cache context, `WithNoCacheContext(perentCtx)` will discard the cache data, so it will be safe to keep the context for a long time. - It will be fine to treat an original context as a cache context, like `GetContextData(context.Backgraud())`, no warning logs will be printed. Some cases about nesting: 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` means `WithCacheContext` - `WithNo` means `WithNoCacheContext` So: - `With(ctx)` -> *A(ctx)* - `With(With(ctx))` -> *A(ctx)*, not *B(A(ctx))* - `With(With(With(ctx)))` -> *A(ctx)*, not *C(B(A(ctx)))* - `WithNo(ctx)` -> *ctx*, not *~A~(ctx)* - `WithNo(With(ctx))` -> *~A~(ctx)* - `WithNo(WithNo(With(ctx)))` -> *~A~(ctx)*, not *~B~(~A~(ctx))* - `With(WithNo(With(ctx)))` -> *B(~A~(ctx))* - `WithNo(With(WithNo(With(ctx))))` -> *~B~(~A~(ctx))* - `With(WithNo(With(WithNo(With(ctx)))))` -> *C(~B~(~A~(ctx)))*
179 lines
5 KiB
Go
179 lines
5 KiB
Go
// Copyright 2022 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package cache
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import (
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"context"
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"sync"
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"time"
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"code.gitea.io/gitea/modules/log"
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)
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// cacheContext is a context that can be used to cache data in a request level context
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// This is useful for caching data that is expensive to calculate and is likely to be
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// used multiple times in a request.
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type cacheContext struct {
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data map[any]map[any]any
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lock sync.RWMutex
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created time.Time
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discard bool
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}
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func (cc *cacheContext) Get(tp, key any) any {
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cc.lock.RLock()
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defer cc.lock.RUnlock()
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return cc.data[tp][key]
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}
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func (cc *cacheContext) Put(tp, key, value any) {
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cc.lock.Lock()
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defer cc.lock.Unlock()
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if cc.discard {
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return
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}
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d := cc.data[tp]
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if d == nil {
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d = make(map[any]any)
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cc.data[tp] = d
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}
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d[key] = value
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}
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func (cc *cacheContext) Delete(tp, key any) {
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cc.lock.Lock()
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defer cc.lock.Unlock()
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delete(cc.data[tp], key)
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}
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func (cc *cacheContext) Discard() {
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cc.lock.Lock()
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defer cc.lock.Unlock()
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cc.data = nil
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cc.discard = true
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}
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func (cc *cacheContext) isDiscard() bool {
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cc.lock.RLock()
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defer cc.lock.RUnlock()
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return cc.discard
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}
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// cacheContextLifetime is the max lifetime of cacheContext.
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// Since cacheContext is used to cache data in a request level context, 10s is enough.
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// If a cacheContext is used more than 10s, it's probably misuse.
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const cacheContextLifetime = 10 * time.Second
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var timeNow = time.Now
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func (cc *cacheContext) Expired() bool {
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return timeNow().Sub(cc.created) > cacheContextLifetime
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}
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var cacheContextKey = struct{}{}
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/*
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Since there are both WithCacheContext and WithNoCacheContext,
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it may be confusing when there is nesting.
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Some cases to explain the design:
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When:
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- A, B or C means a cache context.
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- A', B' or C' means a discard cache context.
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- ctx means context.Backgrand().
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- A(ctx) means a cache context with ctx as the parent context.
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- B(A(ctx)) means a cache context with A(ctx) as the parent context.
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- With is alias of WithCacheContext.
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- WithNo is alias of WithNoCacheContext.
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So:
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- With(ctx) -> A(ctx)
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- With(With(ctx)) -> A(ctx), not B(A(ctx)), always reuse parent cache context if possible.
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- With(With(With(ctx))) -> A(ctx), not C(B(A(ctx))), ditto.
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- WithNo(ctx) -> ctx, not A'(ctx), don't create new cache context if we don't have to.
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- WithNo(With(ctx)) -> A'(ctx)
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- WithNo(WithNo(With(ctx))) -> A'(ctx), not B'(A'(ctx)), don't create new cache context if we don't have to.
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- With(WithNo(With(ctx))) -> B(A'(ctx)), not A(ctx), never reuse a discard cache context.
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- WithNo(With(WithNo(With(ctx)))) -> B'(A'(ctx))
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- With(WithNo(With(WithNo(With(ctx))))) -> C(B'(A'(ctx))), so there's always only one not-discard cache context.
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*/
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func WithCacheContext(ctx context.Context) context.Context {
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if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
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if !c.isDiscard() {
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// reuse parent context
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return ctx
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}
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}
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return context.WithValue(ctx, cacheContextKey, &cacheContext{
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data: make(map[any]map[any]any),
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created: timeNow(),
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})
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}
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func WithNoCacheContext(ctx context.Context) context.Context {
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if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
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// The caller want to run long-life tasks, but the parent context is a cache context.
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// So we should disable and clean the cache data, or it will be kept in memory for a long time.
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c.Discard()
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return ctx
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}
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return ctx
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}
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func GetContextData(ctx context.Context, tp, key any) any {
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if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
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if c.Expired() {
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// The warning means that the cache context is misused for long-life task,
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// it can be resolved with WithNoCacheContext(ctx).
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log.Warn("cache context is expired, may be misused for long-life tasks: %v", c)
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return nil
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}
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return c.Get(tp, key)
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}
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return nil
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}
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func SetContextData(ctx context.Context, tp, key, value any) {
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if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
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if c.Expired() {
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// The warning means that the cache context is misused for long-life task,
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// it can be resolved with WithNoCacheContext(ctx).
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log.Warn("cache context is expired, may be misused for long-life tasks: %v", c)
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return
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}
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c.Put(tp, key, value)
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return
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}
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}
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func RemoveContextData(ctx context.Context, tp, key any) {
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if c, ok := ctx.Value(cacheContextKey).(*cacheContext); ok {
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if c.Expired() {
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// The warning means that the cache context is misused for long-life task,
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// it can be resolved with WithNoCacheContext(ctx).
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log.Warn("cache context is expired, may be misused for long-life tasks: %v", c)
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return
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}
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c.Delete(tp, key)
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}
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}
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// GetWithContextCache returns the cache value of the given key in the given context.
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func GetWithContextCache[T any](ctx context.Context, cacheGroupKey string, cacheTargetID any, f func() (T, error)) (T, error) {
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v := GetContextData(ctx, cacheGroupKey, cacheTargetID)
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if vv, ok := v.(T); ok {
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return vv, nil
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}
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t, err := f()
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if err != nil {
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return t, err
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}
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SetContextData(ctx, cacheGroupKey, cacheTargetID, t)
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return t, nil
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}
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