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gitea/templates/repo/issue
Lunny Xiao bd820aa9c5
Add context cache as a request level cache (#22294)
To avoid duplicated load of the same data in an HTTP request, we can set
a context cache to do that. i.e. Some pages may load a user from a
database with the same id in different areas on the same page. But the
code is hidden in two different deep logic. How should we share the
user? As a result of this PR, now if both entry functions accept
`context.Context` as the first parameter and we just need to refactor
`GetUserByID` to reuse the user from the context cache. Then it will not
be loaded twice on an HTTP request.

But of course, sometimes we would like to reload an object from the
database, that's why `RemoveContextData` is also exposed.

The core context cache is here. It defines a new context
```go
type cacheContext struct {
	ctx  context.Context
	data map[any]map[any]any
        lock sync.RWMutex
}

var cacheContextKey = struct{}{}

func WithCacheContext(ctx context.Context) context.Context {
	return context.WithValue(ctx, cacheContextKey, &cacheContext{
		ctx:  ctx,
		data: make(map[any]map[any]any),
	})
}
```

Then you can use the below 4 methods to read/write/del the data within
the same context.

```go
func GetContextData(ctx context.Context, tp, key any) any
func SetContextData(ctx context.Context, tp, key, value any)
func RemoveContextData(ctx context.Context, tp, key any)
func GetWithContextCache[T any](ctx context.Context, cacheGroupKey string, cacheTargetID any, f func() (T, error)) (T, error)
```

Then let's take a look at how `system.GetString` implement it.

```go
func GetSetting(ctx context.Context, key string) (string, error) {
	return cache.GetWithContextCache(ctx, contextCacheKey, key, func() (string, error) {
		return cache.GetString(genSettingCacheKey(key), func() (string, error) {
			res, err := GetSettingNoCache(ctx, key)
			if err != nil {
				return "", err
			}
			return res.SettingValue, nil
		})
	})
}
```

First, it will check if context data include the setting object with the
key. If not, it will query from the global cache which may be memory or
a Redis cache. If not, it will get the object from the database. In the
end, if the object gets from the global cache or database, it will be
set into the context cache.

An object stored in the context cache will only be destroyed after the
context disappeared.
2 years ago
..
fields Support Issue forms and PR forms (#20987) 2 years ago
labels Optimize html templates (#22080) 2 years ago
view_content Add context cache as a request level cache (#22294) 2 years ago
branch_selector_field.tmpl Move helpers to be prefixed with `gt-` (#22879) 2 years ago
choose.tmpl Add main landmark to templates and adjust titles (#22670) 2 years ago
comment_tab.tmpl Use link in UI which returned a relative url but not html_url which contains an absolute url (#21986) 2 years ago
label_precolors.tmpl Fix purple color in suggested label colors (#18241) 3 years ago
labels.tmpl Add main landmark to templates and adjust titles (#22670) 2 years ago
list.tmpl Add context cache as a request level cache (#22294) 2 years ago
milestone_issues.tmpl Add context cache as a request level cache (#22294) 2 years ago
milestone_new.tmpl Add main landmark to templates and adjust titles (#22670) 2 years ago
milestones.tmpl Move helpers to be prefixed with `gt-` (#22879) 2 years ago
navbar.tmpl Add some headings to repo views (#22869) 2 years ago
new.tmpl Add main landmark to templates and adjust titles (#22670) 2 years ago
new_form.tmpl Add context cache as a request level cache (#22294) 2 years ago
openclose.tmpl Move helpers to be prefixed with `gt-` (#22879) 2 years ago
search.tmpl Issues: add Project filter to issues list and search (#22544) 2 years ago
view.tmpl Add main landmark to templates and adjust titles (#22670) 2 years ago
view_content.tmpl Add context cache as a request level cache (#22294) 2 years ago
view_title.tmpl Move helpers to be prefixed with `gt-` (#22879) 2 years ago