problem: lag is not observed on bitcoin

src/main/kotlin/io/emeraldpay/dshackle/upstream/HeadLagObserver.kt

@@ -21,8 +21,10 @@ import org.slf4j.LoggerFactory
 import org.springframework.context.Lifecycle
 import reactor.core.Disposable
 import reactor.core.publisher.Flux
+import reactor.core.scheduler.Schedulers
 import reactor.util.function.Tuple2
 import reactor.util.function.Tuples
+import java.time.Duration
 
 /**
  * Observer group of upstreams and defined a distance in blocks (lag) between a leader (best height/difficulty) and
@@ -38,6 +40,7 @@ abstract class HeadLagObserver(
     private var current: Disposable? = null
 
     override fun start() {
+        current?.dispose()
         current = subscription().subscribe { }
     }
 
@@ -61,12 +64,15 @@ abstract class HeadLagObserver(
     fun probeFollowers(top: BlockContainer): Flux<Tuple2<Long, Upstream>> {
         return Flux.fromIterable(followers)
                 .parallel(followers.size)
-                .flatMap { mapLagging(top, it, getCurrentBlocks(it)) }
+                .flatMap { up -> mapLagging(top, up, getCurrentBlocks(up)).subscribeOn(Schedulers.elastic()) }
                 .sequential()
                 .onErrorContinue { t, _ -> log.warn("Failed to update lagging distance", t) }
     }
 
-    abstract fun getCurrentBlocks(up: Upstream): Flux<BlockContainer>
+    open fun getCurrentBlocks(up: Upstream): Flux<BlockContainer> {
+        val head = up.getHead()
+        return head.getFlux().take(Duration.ofSeconds(1))
+    }
 
     fun mapLagging(top: BlockContainer, up: Upstream, blocks: Flux<BlockContainer>): Flux<Tuple2<Long, Upstream>> {
         return blocks
@@ -78,11 +84,14 @@ abstract class HeadLagObserver(
                 }
     }
 
-    abstract fun extractDistance(top: BlockContainer, curr: BlockContainer): Long
-
-    fun forkDistance(top: BlockContainer, curr: BlockContainer): Long {
-        //TODO look for common ancestor? though it may be a corruption
-        return 6
+    open fun extractDistance(top: BlockContainer, curr: BlockContainer): Long {
+        return when {
+            curr.height > top.height -> if (curr.difficulty >= top.difficulty) 0 else forkDistance(top, curr)
+            curr.height == top.height -> if (curr.difficulty == top.difficulty) 0 else forkDistance(top, curr)
+            else -> top.height - curr.height
+        }
     }
 
+    abstract fun forkDistance(top: BlockContainer, curr: BlockContainer): Long
+
 }

src/main/kotlin/io/emeraldpay/dshackle/upstream/bitcoin/BitcoinHeadLagObserver.kt

@@ -0,0 +1,38 @@
+/**
+ * Copyright (c) 2020 EmeraldPay, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.emeraldpay.dshackle.upstream.bitcoin
+
+import io.emeraldpay.dshackle.data.BlockContainer
+import io.emeraldpay.dshackle.upstream.Head
+import io.emeraldpay.dshackle.upstream.HeadLagObserver
+import io.emeraldpay.dshackle.upstream.Upstream
+import org.slf4j.LoggerFactory
+
+class BitcoinHeadLagObserver(
+        master: Head,
+        followers: Collection<Upstream>
+) : HeadLagObserver(master, followers) {
+
+    companion object {
+        private val log = LoggerFactory.getLogger(BitcoinHeadLagObserver::class.java)
+    }
+
+    override fun forkDistance(top: BlockContainer, curr: BlockContainer): Long {
+        //TODO fetch actual blocks
+        return 3
+    }
+
+}

src/main/kotlin/io/emeraldpay/dshackle/upstream/bitcoin/BitcoinMultistream.kt

@@ -64,8 +64,8 @@ open class BitcoinMultistream(
             val newHead = MergedHead(upstreams.map { it.getHead() }).apply {
                 this.start()
             }
-//            val lagObserver = TODO
-//            this.lagObserver = lagObserver
+            val lagObserver = BitcoinHeadLagObserver(newHead, upstreams)
+            this.lagObserver = lagObserver
             newHead
         }
         onHeadUpdated(head)

src/main/kotlin/io/emeraldpay/dshackle/upstream/ethereum/EthereumHeadLagObserver.kt

@@ -33,16 +33,9 @@ class EthereumHeadLagObserver(
         private val log = LoggerFactory.getLogger(EthereumHeadLagObserver::class.java)
     }
 
-    override fun getCurrentBlocks(up: Upstream): Flux<BlockContainer> {
-        val head = up.getHead()
-        return head.getFlux().take(Duration.ofSeconds(1))
+    override fun forkDistance(top: BlockContainer, curr: BlockContainer): Long {
+        //TODO look for common ancestor? though it may be a corruption
+        return 6
     }
 
-    override fun extractDistance(top: BlockContainer, curr: BlockContainer): Long {
-        return when {
-            curr.height > top.height -> if (curr.difficulty >= top.difficulty) 0 else forkDistance(top, curr)
-            curr.height == top.height -> if (curr.difficulty == top.difficulty) 0 else forkDistance(top, curr)
-            else -> top.height - curr.height
-        }
-    }
 }