115 lines
3.7 KiB
Markdown
115 lines
3.7 KiB
Markdown
# go-cache
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go-cache is an in-memory key:value store/cache similar to memcached that is
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suitable for applications running on a single machine. Its major advantage is
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that, being essentially a thread-safe `map[string]interface{}` with expiration
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times, it doesn't need to serialize or transmit its contents over the network.
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Any object can be stored, for a given duration or forever, and the cache can be
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safely used by multiple goroutines.
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Although go-cache isn't meant to be used as a persistent datastore, the entire
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cache can be saved to and loaded from a file (using `c.Items()` to retrieve the
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items map to serialize, and `NewFrom()` to create a cache from a deserialized
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one) to recover from downtime quickly. (See the docs for `NewFrom()` for caveats.)
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When creating a cache object using `NewWithLRU()`, if you set the maxItems value
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above 0, the LRU functionality is enabled. The cache automatically updates a
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timestamp every time a given item is retrieved. In the background, the janitor takes
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care of deleting items that have expired because of staleness, or are
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least-recently-used when the cache is under pressure. Whatever you set your purge
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interval to controls when the item will actually be removed from the cache. If you
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don't want to use the janitor, and wish to manually purge LRU items, then
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`c.DeleteLRU(n)` where `n` is the number of items you'd like to purge.
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### Installation
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`go get github.com/pmylund/go-cache`
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### Usage
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import (
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"fmt"
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"github.com/pmylund/go-cache"
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)
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func main() {
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// Create a cache with a default expiration time of 5 minutes, and which
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// purges expired items every 30 seconds
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c := cache.New(5*time.Minute, 30*time.Second)
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// Set the value of the key "foo" to "bar", with the default expiration time
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c.Set("foo", "bar", cache.DefaultExpiration)
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// Set the value of the key "baz" to 42, with no expiration time
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// (the item won't be removed until it is re-set, or removed using
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// c.Delete("baz")
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c.Set("baz", 42, cache.NoExpiration)
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// Get the string associated with the key "foo" from the cache
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foo, found := c.Get("foo")
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if found {
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fmt.Println(foo)
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}
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// Since Go is statically typed, and cache values can be anything, type
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// assertion is needed when values are being passed to functions that don't
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// take arbitrary types, (i.e. interface{}). The simplest way to do this for
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// values which will only be used once--e.g. for passing to another
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// function--is:
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foo, found := c.Get("foo")
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if found {
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MyFunction(foo.(string))
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}
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// This gets tedious if the value is used several times in the same function.
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// You might do either of the following instead:
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if x, found := c.Get("foo"); found {
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foo := x.(string)
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// ...
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}
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// or
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var foo string
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if x, found := c.Get("foo"); found {
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foo = x.(string)
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}
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// ...
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// foo can then be passed around freely as a string
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// Want performance? Store pointers!
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c.Set("foo", &MyStruct, cache.DefaultExpiration)
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if x, found := c.Get("foo"); found {
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foo := x.(*MyStruct)
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// ...
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}
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// If you store a reference type like a pointer, slice, map or channel, you
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// do not need to run Set if you modify the underlying data. The cached
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// reference points to the same memory, so if you modify a struct whose
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// pointer you've stored in the cache, retrieving that pointer with Get will
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// point you to the same data:
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foo := &MyStruct{Num: 1}
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c.Set("foo", foo, cache.DefaultExpiration)
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// ...
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x, _ := c.Get("foo")
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foo := x.(*MyStruct)
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fmt.Println(foo.Num)
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// ...
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foo.Num++
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// ...
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x, _ := c.Get("foo")
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foo := x.(*MyStruct)
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foo.Println(foo.Num)
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// will print:
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// 1
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// 2
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}
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### Reference
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`godoc` or [http://godoc.org/github.com/pmylund/go-cache](http://godoc.org/github.com/pmylund/go-cache)
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