go-cache使用

安装

1 go get github.com/patrickmn/go-cache

使用方法

import (
	"fmt"
	"github.com/patrickmn/go-cache"
	"time"
)

func main() {
	// Create a cache with a default expiration time of 5 minutes, and which
	// purges expired items every 10 minutes
　　　　 // 默认5分钟过期，每10分钟删除过期的项目
	c := cache.New(5*time.Minute, 10*time.Minute)

	// Set the value of the key "foo" to "bar", with the default expiration time
        // 设置缓存，使用默认过期时间
	c.Set("foo", "bar", cache.DefaultExpiration)

	// Set the value of the key "baz" to 42, with no expiration time
	// (the item won't be removed until it is re-set, or removed using
	// c.Delete("baz")
        // 使用不过期策略，除非重新设置了或者使用了Delete方法，否则数据将一直不会被删除，即使是每10分钟的清理也不会
	c.Set("baz", 42, cache.NoExpiration)

	// Get the string associated with the key "foo" from the cache
	foo, found := c.Get("foo")
	if found {
		fmt.Println(foo)
	}

	// Since Go is statically typed, and cache values can be anything, type
	// assertion is needed when values are being passed to functions that don't
	// take arbitrary types, (i.e. interface{}). The simplest way to do this for
	// values which will only be used once--e.g. for passing to another
	// function--is:
	foo, found := c.Get("foo")
	if found {
		MyFunction(foo.(string))
	}

	// This gets tedious if the value is used several times in the same function.
	// You might do either of the following instead:
	if x, found := c.Get("foo"); found {
		foo := x.(string)
		// ...
	}
	// or
	var foo string
	if x, found := c.Get("foo"); found {
		foo = x.(string)
	}
	// ...
	// foo can then be passed around freely as a string

	// Want performance? Store pointers!
	c.Set("foo", &MyStruct, cache.DefaultExpiration)
	if x, found := c.Get("foo"); found {
		foo := x.(*MyStruct)
			// ...
	}
}

过期机制

过期有两种，一种是时间过期，一种是淘汰过期。Guava在构建Cache对象时，可以通过CacheBuilder类的expireAfterAccess和expireAfterWrite两个方法为缓存中的对象指定过期时间，过期的对象将会被缓存自动删除。其中，expireAfterWrite方法指定对象被写入到缓存后多久过期，expireAfterAccess指定对象多久没有被访问后过期。go-cache采用的是时间过期方法，且仅支持expireAfterWrite。

GC

go-cache使用了goroutine执行自动过期清理。当整个cache都不再被使用者需要了，应该被GC，但是由于后台清理goroutine的存在，整个cache将不会被回收掉。go-cache中使用了runtime.SetFinalizer，

func newCacheWithJanitor(de time.Duration, ci time.Duration, m map[string]Item) *Cache {
	c := newCache(de, m)
	// This trick ensures that the janitor goroutine (which--granted it
	// was enabled--is running DeleteExpired on c forever) does not keep
	// the returned C object from being garbage collected. When it is
	// garbage collected, the finalizer stops the janitor goroutine, after
	// which c can be collected.
	C := &Cache{c}
	if ci > 0 {
		runJanitor(c, ci)
		runtime.SetFinalizer(C, stopJanitor)
	}
	return C
}

对SetFinalizer的解释，我引用下别人的