65 lines
1.6 KiB
Go
65 lines
1.6 KiB
Go
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/*
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Copyright 2012 Google Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Package singleflight provides a duplicate function call suppression
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// mechanism.
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package singleflight
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import "sync"
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// call is an in-flight or completed Do call
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type call struct {
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wg sync.WaitGroup
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val interface{}
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err error
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}
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// Group represents a class of work and forms a namespace in which
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// units of work can be executed with duplicate suppression.
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type Group struct {
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mu 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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func (g *Group) Do(key string, fn func() (interface{}, error)) (interface{}, error) {
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g.mu.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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g.mu.Unlock()
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c.wg.Wait()
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return c.val, c.err
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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.mu.Unlock()
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c.val, c.err = fn()
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c.wg.Done()
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g.mu.Lock()
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delete(g.m, key)
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g.mu.Unlock()
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return c.val, c.err
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}
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