java - 咖啡因:当AsyncLoader无法刷新时，请使用过时的值

Question

我想配置Caffeine缓存以在加载程序无法刷新缓存时返回陈旧的结果。以下Kotlin代码演示了这种情况:

    @Test
    fun `completeble future`() = runBlocking {
        val cache = Caffeine.newBuilder()
            .refreshAfterWrite(Duration.ofSeconds(1))
            .expireAfterWrite(Duration.ofSeconds(1))
            .buildAsync<String, String> { key: String, executor ->
                GlobalScope.future(executor.asCoroutineDispatcher()) {
                    throw Exception("== Error ==")
                }
            }

        cache.put("id", CompletableFuture.completedFuture("value"))

        delay(2000)

        assertEquals("value", cache.get("id").await())
    }

我希望此测试通过，但会收到以下错误:

WARNING: Exception thrown during asynchronous load
java.lang.Exception: == Error ==
    at fsra.manager.TranslationManagerImplTest$completeble future$1$cache$1$1.invokeSuspend(TranslationManagerImplTest.kt:93)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:241)
    at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1426)
    at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
    at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
    at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
    at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
    at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)




java.lang.Exception: == Error ==

    at fsra.manager.TranslationManagerImplTest$completeble future$1$cache$1$1.invokeSuspend(TranslationManagerImplTest.kt:93)
    at |b|b|b(Coroutine boundary.|b(|b)
    at fsra.manager.TranslationManagerImplTest$completeble future$1.invokeSuspend(TranslationManagerImplTest.kt:101)
Caused by: java.lang.Exception: == Error ==
    at fsra.manager.TranslationManagerImplTest$completeble future$1$cache$1$1.invokeSuspend(TranslationManagerImplTest.kt:93)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:241)
    at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1426)
    at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
    at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
    at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
    at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
    at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)

我用Kotlin编写了代码，但我认为该问题与Kotlin协程无关。我想将Caffeine配置为在刷新时不抛出，而是在缓存中返回先前的结果。

Answer 1

高速缓存设置为在1秒后过期条目，测试等待2秒。然后，由于该条目不可用，因此下一个调用将强制重新加载它，并且引发异常。

大于或等于到期时间时，刷新不起作用。小于时，该条目是陈旧但可用的，因此将其返回并异步重新加载。这是为了使热门项目(例如配置)可以保留在缓存中，而不会导致定期重新加载。不受欢迎的项目是在到期间隔内未访问的项目，可以将其逐出。如果刷新无法成功，则到期将开始，条目将被删除，因为到期设置了认为可用的最大时间。

较大的到期值(例如5秒)将通过测试。如果您的用例是定期盲目地重新加载所有缓存内容，则可以使用常规的Map和ScheduledExecutorService刷新它。