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57 lines
1.4 KiB
57 lines
1.4 KiB
// Copyright 2013 The Go Authors. All rights reserved. |
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// Use of this source code is governed by a BSD-style |
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// license that can be found in the LICENSE file. |
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// Adapted for dns package usage by Miek Gieben. |
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package dns |
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import "sync" |
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import "time" |
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// call is an in-flight or completed singleflight.Do call |
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type call struct { |
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wg sync.WaitGroup |
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val *Msg |
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rtt time.Duration |
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err error |
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dups int |
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} |
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// singleflight represents a class of work and forms a namespace in |
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// which units of work can be executed with duplicate suppression. |
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type singleflight struct { |
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sync.Mutex // protects m |
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m map[string]*call // lazily initialized |
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} |
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// Do executes and returns the results of the given function, making |
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// sure that only one execution is in-flight for a given key at a |
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// time. If a duplicate comes in, the duplicate caller waits for the |
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// original to complete and receives the same results. |
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// The return value shared indicates whether v was given to multiple callers. |
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func (g *singleflight) Do(key string, fn func() (*Msg, time.Duration, error)) (v *Msg, rtt time.Duration, err error, shared bool) { |
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g.Lock() |
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if g.m == nil { |
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g.m = make(map[string]*call) |
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} |
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if c, ok := g.m[key]; ok { |
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c.dups++ |
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g.Unlock() |
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c.wg.Wait() |
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return c.val, c.rtt, c.err, true |
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} |
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c := new(call) |
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c.wg.Add(1) |
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g.m[key] = c |
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g.Unlock() |
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c.val, c.rtt, c.err = fn() |
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c.wg.Done() |
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g.Lock() |
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delete(g.m, key) |
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g.Unlock() |
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return c.val, c.rtt, c.err, c.dups > 0 |
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}
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