move prepare to fix race condition

When importing blocks quickly, there's a chance that some state from the
block after the mark block makes it into the database before the node
added listener is fully attached. This means that state after the mark
block could be removed. This creates the node added listener once and
for all before the block added event observer so the race never happens.

Signed-off-by: Ratan Rai Sur <[email protected]>

ethereum/core/src/main/java/org/hyperledger/besu/ethereum/worldstate/Pruner.java

@@ -58,6 +58,7 @@ public Pruner(
 
   public void start() {
     LOG.info("Starting Pruner.");
+    pruningStrategy.prepare();
     blockchain.observeBlockAdded((event, blockchain) -> handleNewBlock(event));
   }
 
@@ -73,7 +74,6 @@ private void handleNewBlock(final BlockAddedEvent event) {
 
     final long blockNumber = event.getBlock().getHeader().getNumber();
     if (state.compareAndSet(State.IDLE, State.MARK_BLOCK_CONFIRMATIONS_AWAITING)) {
-      pruningStrategy.prepare();
       markBlockNumber = blockNumber;
     } else if (blockNumber >= markBlockNumber + blockConfirmations
         && state.compareAndSet(State.MARK_BLOCK_CONFIRMATIONS_AWAITING, State.MARKING)) {
@@ -107,7 +107,6 @@ private void sweep() {
     execute(
         () -> {
           pruningStrategy.sweepBefore(markBlockNumber);
-          pruningStrategy.cleanup();
           state.compareAndSet(State.SWEEPING, State.IDLE);
         });
   }