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)))*
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