59 lines
1.4 KiB
Go
59 lines
1.4 KiB
Go
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// I put this here to look at and think about
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// from mod/sumdb/cache.go
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// Parallel cache.
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// This file is copied from cmd/go/internal/par.
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package forgepb
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import (
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"sync"
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"sync/atomic"
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)
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// parCache runs an action once per key and caches the result.
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type parCache struct {
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m sync.Map
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}
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type cacheEntry struct {
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done uint32
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mu sync.Mutex
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result interface{}
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}
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// Do calls the function f if and only if Do is being called for the first time with this key.
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// No call to Do with a given key returns until the one call to f returns.
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// Do returns the value returned by the one call to f.
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func (c *parCache) Do(key interface{}, f func() interface{}) interface{} {
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entryIface, ok := c.m.Load(key)
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if !ok {
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entryIface, _ = c.m.LoadOrStore(key, new(cacheEntry))
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}
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e := entryIface.(*cacheEntry)
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if atomic.LoadUint32(&e.done) == 0 {
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e.mu.Lock()
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if atomic.LoadUint32(&e.done) == 0 {
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e.result = f()
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atomic.StoreUint32(&e.done, 1)
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}
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e.mu.Unlock()
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}
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return e.result
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}
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// Get returns the cached result associated with key.
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// It returns nil if there is no such result.
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// If the result for key is being computed, Get does not wait for the computation to finish.
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func (c *parCache) Get(key interface{}) interface{} {
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entryIface, ok := c.m.Load(key)
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if !ok {
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return nil
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}
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e := entryIface.(*cacheEntry)
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if atomic.LoadUint32(&e.done) == 0 {
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return nil
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}
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return e.result
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}
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