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Aedile

Aedile is a simple Kotlin wrapper for Caffeine which prefers coroutines rather than Java futures.

See changelog

Features

Suspendable functions: Rather than use Java's CompletableFutures, all operations on Aedile are suspendable and executed in their own coroutines.
Backed by Caffeine: This is not a new cache implementation with its own bugs and quirks, but a simple wrapper around Caffeine which has been used on the JVM for years.
Kotlin durations: Specify expiration and refresh times in kotlin.time.Duration rather than Java durations.
Kotlin functions: Whereever a function is required - eg eviction listener - Aedile supports Kotlin functions rather than Java's Function interface.

Usage

Add Aedile to your build:

implementation 'com.sksamuel.aedile:aedile-core:<version>'

Next, in your code, create a cache through the cache builder with the cacheBuilder() function, supplying the key / value types.

val cache = cacheBuilder<String, String>().build()

With this cache we can request values if present, or supply a suspendable function to compute them.

val value1 = cache.getIfPresent("foo") // value or null

val value2 = cache.get("foo") {
   delay(100) // look ma, we support suspendable functions!
   "value"
}

The build function supports a generic compute function which is used if no specific compute function is provided.

val cache = cacheBuilder<String, String>().build {
   delay(1)
   "value"
}

cache.get("foo") // uses default compute
cache.get("bar") { "other" } // uses specific compute function

Configuration

When creating the cache, Aedile supports most Caffeine configuration options. The exception is softValues and weakValues which are not supported with asynchronous operations. Since Aedile's purpose is to support coroutines, these options are ignored.

To configure the builder we supply a configuration lambda:

val cache = cacheBuilder<String, String> {
   maximumSize = 100
   initialCapacity = 10
}.build()

Evictions

Caffeine provides different approaches to eviction:

expireAfterAccess(duration): Expire entries after the specified duration has passed since the entry was last accessed by a read or a write. This could be desirable if the cached data is bound to a session and expires due to inactivity.
expireAfterWrite(duration): Expire entries after the specified duration has passed since the entry was created, or the most recent replacement of the value. This could be desirable if cached data grows stale after a certain amount of time.
expireAfter(expiry): Pass an implementation of Expiry which has methods for specifying that expiry should occur either after a duration from insert, a duration from last refresh, or a duration from last read.
invalidate / invalidateAll: Programatically remove entries based on their key(s) or remove all entries. In the case of a loading cache, any currently loading values may not be removed.

You can specify a suspendable function to listen to evictions:

val cache = cacheBuilder<String, String> {
   evictionListener = { key, value, cause ->
      when (cause) {
         RemovalCause.SIZE -> println("Removed due to size constraints")
         else -> delay(100) // suspendable for no real reason, but just to show you can!!
      }
   }
}.build()

Specify Dispatchers

By default, Aedile will use the dispatcher from the calling function for executing the compute functions. You can specify your own dispatcher when configuring the builder.

val cacheDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
val cache = cacheBuilder<String, String>() {
   this.dispatcher = cacheDispatcher
}.build()

You can also specify a custom CoroutineScope if required. Note that this scope should not be cancelled or closed while the cache is in use.

Metrics

Aedile provides Micrometer integration which simply delegates to the Caffeine micrometer support. To use this, import the com.sksamuel.aedile:aedile-micrometer module, and bind to a micrometer registry:

CacheMetrics(cache, "my-cache-name").bindTo(registry)
// or
LoadingCacheMetrics(cache, "my-cache-name").bindTo(registry)