try fix tests

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

@@ -20,6 +20,7 @@ import io.emeraldpay.dshackle.upstream.forkchoice.ForkChoice
 import org.slf4j.LoggerFactory
 import reactor.core.Disposable
 import reactor.core.publisher.Flux
+import reactor.core.publisher.SignalType
 import reactor.core.publisher.Sinks
 import reactor.core.publisher.Sinks.EmitResult.FAIL_ZERO_SUBSCRIBER
 import reactor.core.publisher.Sinks.EmitResult.OK
@@ -27,6 +28,7 @@ import reactor.core.scheduler.Schedulers
 import reactor.kotlin.core.publisher.toMono
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
+import java.util.concurrent.locks.ReentrantLock
 
 abstract class AbstractHead(
     private val forkChoice: ForkChoice,
@@ -43,6 +45,7 @@ abstract class AbstractHead(
     private val beforeBlockHandlers = ArrayList<Runnable>()
     private var stopping = false
     private var lastHeadUpdated = 0L
+    private val lock = ReentrantLock()
 
     init {
         Executors.newSingleThreadScheduledExecutor().scheduleAtFixedRate(
@@ -50,7 +53,12 @@ abstract class AbstractHead(
                 val delay = System.currentTimeMillis() - lastHeadUpdated
                 if (delay > awaitHeadTimeoutMs) {
                     log.warn("No head updates for $delay ms @ ${this.javaClass} - restart")
-                    start()
+                    try {
+                        lock.tryLock()
+                        start()
+                    } finally {
+                        lock.unlock()
+                    }
                 }
             }, 300, 30, TimeUnit.SECONDS
         )
@@ -71,13 +79,13 @@ abstract class AbstractHead(
                 // close internal stream if upstream is finished, otherwise it gets stuck,
                 // but technically it should never happen during normal work, only when the Head
                 // is stopping
-                if (stopping) {
-                    log.info("Received signal $it - stop emit new head!!!")
+                if (it == SignalType.ON_ERROR && !stopping) {
+                    log.warn("Received signal $it unexpectedly - restart head")
+                    lastHeadUpdated = 0L
+                } else {
+                    log.warn("Received signal $it - stop emit new head!!!")
                     completed = true
                     stream.tryEmitComplete()
-                } else {
-                    log.warn("Received signal $it unexpectedly - restart head")
-                    start()
                 }
             }
             .subscribeOn(Schedulers.boundedElastic())