golang close_chan

Posted 2021-05-24

package memo

type entry struct {
    res   result
    ready chan struct{}
}

func (e *entry) call(f Func, key string) {
    e.res.value, e.res.err = f(key)
    close(e.ready)
}
func (e *entry) deliver(response chan<- result) {
    <-e.ready
    response <- e.res
}

type result struct {
    value interface{}
    err   error
}
type request struct {
    key      string
    response chan<- result
}
type Memo struct {
    requests chan request
}

func (memo *Memo) server(f Func) {
    cache := make(map[string]*entry)
    for req := range memo.requests {
        e := cache[req.key]
        if e == nil {
            e = &entry{ready: make(chan struct{})}
            cache[req.key] = e
            go e.call(f, req.key)
        }
        go e.deliver(req.response)
    }
}

type Func func(key string) (value interface{}, err error)

// factory func
func New(f Func) *Memo {
    memo := &Memo{requests: make(chan request)}
    go memo.server(f)
    return memo
}

func (memo *Memo) Get(key string) (interface{}, error) {
    response := make(chan result)
    memo.requests <- request{key, response}
    res := <-response
    return res.value, res.err
}
func (memo *Memo) Close() {
    close(memo.requests)
}

package memo

import (
    "sync"
)

type entry struct {
    res   result
    ready chan struct{}
}
type result struct {
    value interface{}
    err   error
}
type Memo struct {
    f     Func
    mu    sync.Mutex
    cache map[string]*entry
}
type Func func(key string) (value interface{}, err error)

// factory func
func New(f Func) *Memo {
    return &Memo{f: f, cache: make(map[string]*entry)}
}


func (memo *Memo) Get(key string) (interface{}, error) {
    memo.mu.Lock()
    e := memo.cache[key]
    if e == nil {
        e = &entry{ready: make(chan struct{})}
        memo.cache[key] = e
        memo.mu.Unlock()
        e.res.value, e.res.err = memo.f(key)
        close(e.ready)
    } else {
        memo.mu.Unlock()
        <-e.ready
    }
    return e.res.value, e.res.err
}

json [Golang] golang #golang #snippets中有用的片段

[ fmt ](https://golang.org/pkg/fmt/)
-------
Print any `type`(struct,maps,primitives) with the `key` name 

``` 
fmt.Printf("\n [key] :%+v \n", [value]) 

```

Print Error  

``` 
fmt.Errorf(" \nError: %s", err.Error()) 

```

[ log ](https://golang.org/pkg/log/)
-------------

Print any `type`(struct,maps,primitives) with the `key` name 

``` 
log.Printf("\n [key] :%+v \n", [value]) 

```


[ http  ](https://golang.org/pkg/log/)
-------------

http middleware 

```  
func [middlewareName](h http.Handler) http.Handler {
              return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
              // Do things before request 
           	
              nextMiddleware.ServeHTTP(w, r)
              // Do things after request	  
              })
          } 
```

{
         "http Middleware declaration": {
		"prefix": "md",
		"body": ["func $1(${2:nextMiddleware} http.Handler) http.Handler {\n\treturn http.HandlerFunc(func(${3:w} http.ResponseWriter, ${4:r} *http.Request) {\n\t $5\n\t nextMiddleware.ServeHTTP(${3:w}, ${4:r})\n\t 	  $6\n\t})\n}"],
		"description": "Snippet for http middleware declaration"
	},

	"log.Printf()": {
		"prefix": "lf",
		"body": [
			"log.Printf(\"\\n## ${1:text} ##: %+v\\n\", ${2:value})"
		],
		"description": "log.Printf()"
	},
	"fmt.Printf()": {
		"prefix": "ff",
		"body": [
			"fmt.Printf(\"\\n## ${1:text} ## :%+v \\n\", ${2:value})",
		],
		"description": "log.Printf()"
	}
}