e1464fd317
Fixes https://github.com/docker/distribution/issues/3097 Signed-off-by: Yong Wen Chua <lawliet89@users.noreply.github.com>
120 lines
3 KiB
Go
120 lines
3 KiB
Go
// 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.
|
|
|
|
// Package singleflight provides a duplicate function call suppression
|
|
// mechanism.
|
|
package singleflight
|
|
|
|
import "sync"
|
|
|
|
// call is an in-flight or completed singleflight.Do call
|
|
type call struct {
|
|
wg sync.WaitGroup
|
|
|
|
// These fields are written once before the WaitGroup is done
|
|
// and are only read after the WaitGroup is done.
|
|
val interface{}
|
|
err error
|
|
|
|
// forgotten indicates whether Forget was called with this call's key
|
|
// while the call was still in flight.
|
|
forgotten bool
|
|
|
|
// These fields are read and written with the singleflight
|
|
// mutex held before the WaitGroup is done, and are read but
|
|
// not written after the WaitGroup is done.
|
|
dups int
|
|
chans []chan<- Result
|
|
}
|
|
|
|
// Group represents a class of work and forms a namespace in
|
|
// which units of work can be executed with duplicate suppression.
|
|
type Group struct {
|
|
mu sync.Mutex // protects m
|
|
m map[string]*call // lazily initialized
|
|
}
|
|
|
|
// Result holds the results of Do, so they can be passed
|
|
// on a channel.
|
|
type Result struct {
|
|
Val interface{}
|
|
Err error
|
|
Shared bool
|
|
}
|
|
|
|
// 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 *Group) Do(key string, fn func() (interface{}, error)) (v interface{}, err error, shared bool) {
|
|
g.mu.Lock()
|
|
if g.m == nil {
|
|
g.m = make(map[string]*call)
|
|
}
|
|
if c, ok := g.m[key]; ok {
|
|
c.dups++
|
|
g.mu.Unlock()
|
|
c.wg.Wait()
|
|
return c.val, c.err, true
|
|
}
|
|
c := new(call)
|
|
c.wg.Add(1)
|
|
g.m[key] = c
|
|
g.mu.Unlock()
|
|
|
|
g.doCall(c, key, fn)
|
|
return c.val, c.err, c.dups > 0
|
|
}
|
|
|
|
// DoChan is like Do but returns a channel that will receive the
|
|
// results when they are ready.
|
|
func (g *Group) DoChan(key string, fn func() (interface{}, error)) <-chan Result {
|
|
ch := make(chan Result, 1)
|
|
g.mu.Lock()
|
|
if g.m == nil {
|
|
g.m = make(map[string]*call)
|
|
}
|
|
if c, ok := g.m[key]; ok {
|
|
c.dups++
|
|
c.chans = append(c.chans, ch)
|
|
g.mu.Unlock()
|
|
return ch
|
|
}
|
|
c := &call{chans: []chan<- Result{ch}}
|
|
c.wg.Add(1)
|
|
g.m[key] = c
|
|
g.mu.Unlock()
|
|
|
|
go g.doCall(c, key, fn)
|
|
|
|
return ch
|
|
}
|
|
|
|
// doCall handles the single call for a key.
|
|
func (g *Group) doCall(c *call, key string, fn func() (interface{}, error)) {
|
|
c.val, c.err = fn()
|
|
c.wg.Done()
|
|
|
|
g.mu.Lock()
|
|
if !c.forgotten {
|
|
delete(g.m, key)
|
|
}
|
|
for _, ch := range c.chans {
|
|
ch <- Result{c.val, c.err, c.dups > 0}
|
|
}
|
|
g.mu.Unlock()
|
|
}
|
|
|
|
// Forget tells the singleflight to forget about a key. Future calls
|
|
// to Do for this key will call the function rather than waiting for
|
|
// an earlier call to complete.
|
|
func (g *Group) Forget(key string) {
|
|
g.mu.Lock()
|
|
if c, ok := g.m[key]; ok {
|
|
c.forgotten = true
|
|
}
|
|
delete(g.m, key)
|
|
g.mu.Unlock()
|
|
}
|