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49 lines
1.0 KiB
Go
49 lines
1.0 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 276.
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// Package memo provides a concurrency-safe memoization a function of
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// type Func. Requests for different keys run concurrently.
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// Concurrent requests for the same key result in duplicate work.
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package memo
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import "sync"
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type Memo struct {
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f Func
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mu sync.Mutex // guards cache
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cache map[string]result
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}
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type Func func(string) (interface{}, error)
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type result struct {
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value interface{}
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err error
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}
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func New(f Func) *Memo {
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return &Memo{f: f, cache: make(map[string]result)}
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}
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//!+
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func (memo *Memo) Get(key string) (value interface{}, err error) {
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memo.mu.Lock()
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res, ok := memo.cache[key]
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memo.mu.Unlock()
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if !ok {
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res.value, res.err = memo.f(key)
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// Between the two critical sections, several goroutines
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// may race to compute f(key) and update the map.
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memo.mu.Lock()
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memo.cache[key] = res
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memo.mu.Unlock()
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}
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return res.value, res.err
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}
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//!-
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