/usr/share/gocode/src/github.com/miekg/dns/singleinflight.go is in golang-github-miekg-dns-dev 0.0~git20161018.0.58f52c5-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | // Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Adapted for dns package usage by Miek Gieben.
package dns
import "sync"
import "time"
// call is an in-flight or completed singleflight.Do call
type call struct {
wg sync.WaitGroup
val *Msg
rtt time.Duration
err error
dups int
}
// singleflight represents a class of work and forms a namespace in
// which units of work can be executed with duplicate suppression.
type singleflight struct {
sync.Mutex // protects m
m map[string]*call // lazily initialized
}
// Do executes and returns the results of the given function, making
// sure that only one execution is in-flight for a given key at a
// time. If a duplicate comes in, the duplicate caller waits for the
// original to complete and receives the same results.
// The return value shared indicates whether v was given to multiple callers.
func (g *singleflight) Do(key string, fn func() (*Msg, time.Duration, error)) (v *Msg, rtt time.Duration, err error, shared bool) {
g.Lock()
if g.m == nil {
g.m = make(map[string]*call)
}
if c, ok := g.m[key]; ok {
c.dups++
g.Unlock()
c.wg.Wait()
return c.val, c.rtt, c.err, true
}
c := new(call)
c.wg.Add(1)
g.m[key] = c
g.Unlock()
c.val, c.rtt, c.err = fn()
c.wg.Done()
g.Lock()
delete(g.m, key)
g.Unlock()
return c.val, c.rtt, c.err, c.dups > 0
}
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