blob: 56a15cd57c840444c8eb3635b564335c519a07e3 [file] [log] [blame]
// Copyright 2018 The LUCI Authors.
//
// 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 promise
import (
"context"
"sync"
)
// Map is a map from some key to a promise that does something associated
// with this key.
//
// First call to Get initiates a new promise. All subsequent calls return exact
// same promise (even if it has finished).
type Map struct {
mu sync.RWMutex
m map[interface{}]*Promise
}
// Get either returns an existing promise for the given key or creates and
// immediately launches a new promise.
func (pm *Map) Get(c context.Context, key interface{}, gen Generator) *Promise {
pm.mu.RLock()
p := pm.m[key]
pm.mu.RUnlock()
if p != nil {
return p
}
pm.mu.Lock()
defer pm.mu.Unlock()
if p = pm.m[key]; p == nil {
p = New(c, gen)
if pm.m == nil {
pm.m = make(map[interface{}]*Promise, 1)
}
pm.m[key] = p
}
return p
}