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cache.go
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cache.go
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// Copyright 2022 Google LLC
//
// 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 main
import (
"context"
"fmt"
"sync"
"github.com/ServiceWeaver/weaver"
"github.com/ServiceWeaver/weaver/metrics"
lru "github.com/hashicorp/golang-lru/v2"
)
var (
reads = metrics.NewCounter("chat_cache_reads", "Number of cache reads.")
misses = metrics.NewCounter("chat_cache_misses", "Number of cache misses.")
writes = metrics.NewCounter("chat_cache_writes", "Number of cache writes.")
entries = metrics.NewGauge("chat_cache_entries", "Number of cache entries.")
sizes = metrics.NewHistogram(
"chat_cache_value_sizes_bytes",
"Histogram of sizes, in bytes, of cache values.",
[]float64{10, 100, 1000, 10000, 100000, 1000000},
)
)
const cacheSize = 65536
type LocalCache interface {
Get(_ context.Context, key string) (string, error)
Put(_ context.Context, key, val string) error
}
type localCache struct {
weaver.Implements[LocalCache]
mu sync.Mutex
cache *lru.Cache[string, string]
// TODO: Eviction policy.
}
func (c *localCache) Init(context.Context) error {
cache, err := lru.New[string, string](cacheSize)
c.cache = cache
return err
}
// Get returns the cached value for key, or an error.
func (c *localCache) Get(_ context.Context, key string) (string, error) {
reads.Add(1)
c.mu.Lock()
defer c.mu.Unlock()
v, ok := c.cache.Get(key)
if !ok {
misses.Add(1)
return "", fmt.Errorf("key %q not found in cache", key)
}
return v, nil
}
// Put stores key,val in the cache.
func (c *localCache) Put(_ context.Context, key, val string) error {
writes.Add(1)
sizes.Put(float64(len(val)))
c.mu.Lock()
defer c.mu.Unlock()
c.cache.Add(key, val)
entries.Set(float64(c.cache.Len()))
return nil
}