problem: block height cache doesn't evict when old blocks are added

rel: ce010e50

build.gradle

@@ -104,6 +104,7 @@ dependencies {
     implementation 'org.apache.commons:commons-collections4:4.3'
     implementation 'javax.annotation:javax.annotation-api:1.3.2'
     implementation 'org.bouncycastle:bcprov-jdk15on:1.61'
+    implementation 'com.github.ben-manes.caffeine:caffeine:2.8.5'
 
     implementation "org.slf4j:slf4j-api:$slf4jVersion"
     implementation "org.apache.logging.log4j:log4j-slf4j-impl:2.11.1"

src/main/kotlin/io/emeraldpay/dshackle/cache/HeightCache.kt

@@ -15,41 +15,35 @@
  */
 package io.emeraldpay.dshackle.cache
 
+import com.github.benmanes.caffeine.cache.Caffeine
 import io.emeraldpay.dshackle.data.BlockContainer
 import io.emeraldpay.dshackle.data.BlockId
 import io.emeraldpay.dshackle.reader.Reader
-import org.slf4j.LoggerFactory
 import reactor.core.publisher.Mono
-import java.util.concurrent.ConcurrentHashMap
 
 /**
  * Memory cache for blocks heights, keeps mapping height->hash.
  */
 open class HeightCache(
-        val maxSize: Int = 256
+        maxSize: Int = 512
 ) : Reader<Long, BlockId> {
 
-    companion object {
-        private val log = LoggerFactory.getLogger(HeightCache::class.java)
-    }
-
-    private val heights = ConcurrentHashMap<Long, BlockId>()
+    private val heights = Caffeine.newBuilder()
+            .maximumSize(maxSize.toLong())
+            .build<Long, BlockId>()
 
     override fun read(key: Long): Mono<BlockId> {
-        return Mono.justOrEmpty(heights[key])
+        return Mono.justOrEmpty(heights.getIfPresent(key))
     }
 
     open fun add(block: BlockContainer): BlockId? {
-        val existing = heights[block.height]
-        heights[block.height] = block.hash
-
-        // evict old numbers if full
-        var dropHeight = block.height - maxSize
-        while (heights.size > maxSize && dropHeight < block.height) {
-            heights.remove(dropHeight)
-            dropHeight++
-        }
-
-        return existing
+        val previousId = heights.getIfPresent(block.height)
+        heights.put(block.height, block.hash)
+        return previousId
     }
+
+    fun purge() {
+        heights.cleanUp()
+    }
+
 }

src/test/groovy/io/emeraldpay/dshackle/cache/HeightCacheSpec.groovy

@@ -72,6 +72,7 @@ class HeightCacheSpec extends Specification {
             block.timestamp = Instant.now()
             cache.add(BlockContainer.from(block))
         }
+        cache.purge()
 
         def act1 = cache.read(100).block()
         def act2 = cache.read(101).block()