mirror of
https://github.com/mailgun/groupcache.git
synced 2024-11-16 14:10:04 +00:00
82 lines
2.0 KiB
Go
82 lines
2.0 KiB
Go
/*
|
|
Copyright 2012 Google Inc.
|
|
|
|
Licensed under the Apache License, Version 2.0 (the "License");
|
|
you may not use this file except in compliance with the License.
|
|
You may obtain a copy of the License at
|
|
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
|
|
|
Unless required by applicable law or agreed to in writing, software
|
|
distributed under the License is distributed on an "AS IS" BASIS,
|
|
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
See the License for the specific language governing permissions and
|
|
limitations under the License.
|
|
*/
|
|
|
|
// Package singleflight provides a duplicate function call suppression
|
|
// mechanism.
|
|
package singleflight
|
|
|
|
import (
|
|
"fmt"
|
|
"sync"
|
|
)
|
|
|
|
// call is an in-flight or completed Do call
|
|
type call struct {
|
|
wg sync.WaitGroup
|
|
val interface{}
|
|
err error
|
|
}
|
|
|
|
// 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
|
|
}
|
|
|
|
// 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.
|
|
func (g *Group) Do(key string, fn func() (interface{}, error)) (interface{}, error) {
|
|
g.mu.Lock()
|
|
if g.m == nil {
|
|
g.m = make(map[string]*call)
|
|
}
|
|
if c, ok := g.m[key]; ok {
|
|
g.mu.Unlock()
|
|
c.wg.Wait()
|
|
return c.val, c.err
|
|
}
|
|
c := &call{
|
|
err: fmt.Errorf("singleflight leader panicked"),
|
|
}
|
|
c.wg.Add(1)
|
|
g.m[key] = c
|
|
g.mu.Unlock()
|
|
|
|
defer func() {
|
|
c.wg.Done()
|
|
|
|
g.mu.Lock()
|
|
delete(g.m, key)
|
|
g.mu.Unlock()
|
|
}()
|
|
|
|
c.val, c.err = fn()
|
|
|
|
return c.val, c.err
|
|
}
|
|
|
|
// Lock prevents single flights from occurring for the duration
|
|
// of the provided function. This allows users to clear caches
|
|
// or preform some operation in between running flights.
|
|
func (g *Group) Lock(fn func()) {
|
|
g.mu.Lock()
|
|
defer g.mu.Unlock()
|
|
fn()
|
|
}
|