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/*
* Copyright 2019 gRPC 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 cache implements caches to be used in gRPC.
package cache
import (
"sync"
"time"
)
type cacheEntry struct {
item interface{}
// Note that to avoid deadlocks (potentially caused by lock ordering),
// callback can only be called without holding cache's mutex.
callback func()
timer *time.Timer
// deleted is set to true in Remove() when the call to timer.Stop() fails.
// This can happen when the timer in the cache entry fires around the same
// time that timer.stop() is called in Remove().
deleted bool
}
// TimeoutCache is a cache with items to be deleted after a timeout.
type TimeoutCache struct {
mu sync.Mutex
timeout time.Duration
cache map[interface{}]*cacheEntry
}
// NewTimeoutCache creates a TimeoutCache with the given timeout.
func NewTimeoutCache(timeout time.Duration) *TimeoutCache {
return &TimeoutCache{
timeout: timeout,
cache: make(map[interface{}]*cacheEntry),
}
}
// Add adds an item to the cache, with the specified callback to be called when
// the item is removed from the cache upon timeout. If the item is removed from
// the cache using a call to Remove before the timeout expires, the callback
// will not be called.
//
// If the Add was successful, it returns (newly added item, true). If there is
// an existing entry for the specified key, the cache entry is not be updated
// with the specified item and it returns (existing item, false).
func (c *TimeoutCache) Add(key, item interface{}, callback func()) (interface{}, bool) {
c.mu.Lock()
defer c.mu.Unlock()
if e, ok := c.cache[key]; ok {
return e.item, false
}
entry := &cacheEntry{
item: item,
callback: callback,
}
entry.timer = time.AfterFunc(c.timeout, func() {
c.mu.Lock()
if entry.deleted {
c.mu.Unlock()
// Abort the delete since this has been taken care of in Remove().
return
}
delete(c.cache, key)
c.mu.Unlock()
entry.callback()
})
c.cache[key] = entry
return item, true
}
// Remove the item with the key from the cache.
//
// If the specified key exists in the cache, it returns (item associated with
// key, true) and the callback associated with the item is guaranteed to be not
// called. If the given key is not found in the cache, it returns (nil, false)
func (c *TimeoutCache) Remove(key interface{}) (item interface{}, ok bool) {
c.mu.Lock()
defer c.mu.Unlock()
entry, ok := c.removeInternal(key)
if !ok {
return nil, false
}
return entry.item, true
}
// removeInternal removes and returns the item with key.
//
// caller must hold c.mu.
func (c *TimeoutCache) removeInternal(key interface{}) (*cacheEntry, bool) {
entry, ok := c.cache[key]
if !ok {
return nil, false
}
delete(c.cache, key)
if !entry.timer.Stop() {
// If stop was not successful, the timer has fired (this can only happen
// in a race). But the deleting function is blocked on c.mu because the
// mutex was held by the caller of this function.
//
// Set deleted to true to abort the deleting function. When the lock is
// released, the delete function will acquire the lock, check the value
// of deleted and return.
entry.deleted = true
}
return entry, true
}
// Clear removes all entries, and runs the callbacks if runCallback is true.
func (c *TimeoutCache) Clear(runCallback bool) {
var entries []*cacheEntry
c.mu.Lock()
for key := range c.cache {
if e, ok := c.removeInternal(key); ok {
entries = append(entries, e)
}
}
c.mu.Unlock()
if !runCallback {
return
}
// removeInternal removes entries from cache, and also stops the timer, so
// the callback is guaranteed to be not called. If runCallback is true,
// manual execute all callbacks.
for _, entry := range entries {
entry.callback()
}
}
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