Improve cache context (#23330)

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)))*

modules/cache/context_test.go

@@ -6,6 +6,7 @@ package cache
 import (
 	"context"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -25,7 +26,7 @@ func TestWithCacheContext(t *testing.T) {
 	assert.EqualValues(t, 1, v.(int))
 
 	RemoveContextData(ctx, field, "my_config1")
-	RemoveContextData(ctx, field, "my_config2") // remove an non-exist key
+	RemoveContextData(ctx, field, "my_config2") // remove a non-exist key
 
 	v = GetContextData(ctx, field, "my_config1")
 	assert.Nil(t, v)
@@ -38,4 +39,40 @@ func TestWithCacheContext(t *testing.T) {
 
 	v = GetContextData(ctx, field, "my_config1")
 	assert.EqualValues(t, 1, v)
+
+	now := timeNow
+	defer func() {
+		timeNow = now
+	}()
+	timeNow = func() time.Time {
+		return now().Add(10 * time.Second)
+	}
+	v = GetContextData(ctx, field, "my_config1")
+	assert.Nil(t, v)
+}
+
+func TestWithNoCacheContext(t *testing.T) {
+	ctx := context.Background()
+
+	const field = "system_setting"
+
+	v := GetContextData(ctx, field, "my_config1")
+	assert.Nil(t, v)
+	SetContextData(ctx, field, "my_config1", 1)
+	v = GetContextData(ctx, field, "my_config1")
+	assert.Nil(t, v) // still no cache
+
+	ctx = WithCacheContext(ctx)
+	v = GetContextData(ctx, field, "my_config1")
+	assert.Nil(t, v)
+	SetContextData(ctx, field, "my_config1", 1)
+	v = GetContextData(ctx, field, "my_config1")
+	assert.NotNil(t, v)
+
+	ctx = WithNoCacheContext(ctx)
+	v = GetContextData(ctx, field, "my_config1")
+	assert.Nil(t, v)
+	SetContextData(ctx, field, "my_config1", 1)
+	v = GetContextData(ctx, field, "my_config1")
+	assert.Nil(t, v) // still no cache
 }