Fix BurningManAccountingStore data races

Multiple threads read and write to the accounting blocks list causing
data races. Luckily, the LinkedList threw a ConcurrentModificationException
to limit damage. Now, a ReadWriteLock protects the LinkedList against
data races. Multiple threads can read the list at the same time but only
one thread can write to it. Other writing threads wait until it's their
turn.

Fixes bisq-network#6545

core/src/main/java/bisq/core/dao/burningman/accounting/BurningManAccountingService.java

@@ -49,12 +49,12 @@
 import java.util.Date;
 import java.util.GregorianCalendar;
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 
 import lombok.Getter;
 import lombok.extern.slf4j.Slf4j;
@@ -113,7 +113,9 @@ public void start() {
         CompletableFuture.runAsync(() -> {
             Map<String, BalanceModel> map = new HashMap<>();
             // addAccountingBlockToBalanceModel takes about 500ms for 100k items, so we run it in a non UI thread.
-            getBlocks().forEach(block -> addAccountingBlockToBalanceModel(map, block));
+            getBlocks().forEach(optionalBlock ->
+                    optionalBlock.ifPresent(block -> addAccountingBlockToBalanceModel(map, block))
+            );
             UserThread.execute(() -> balanceModelByBurningManName.putAll(map));
         });
     }
@@ -125,7 +127,7 @@ public void start() {
 
     public void onInitialBlockRequestsComplete() {
         updateBalanceModelByAddress();
-        getBlocks().forEach(this::addAccountingBlockToBalanceModel);
+        getBlocks().forEach(optionalBlock -> optionalBlock.ifPresent(this::addAccountingBlockToBalanceModel));
     }
 
     public void onNewBlockReceived(AccountingBlock accountingBlock) {
@@ -134,7 +136,7 @@ public void onNewBlockReceived(AccountingBlock accountingBlock) {
     }
 
     public void addBlock(AccountingBlock block) throws BlockHashNotConnectingException, BlockHeightNotConnectingException {
-        if (!getBlocks().contains(block)) {
+        if (!burningManAccountingStoreService.containsAccountingBlock(block)) {
             Optional<AccountingBlock> optionalLastBlock = getLastBlock();
             if (optionalLastBlock.isPresent()) {
                 AccountingBlock lastBlock = optionalLastBlock.get();
@@ -160,11 +162,18 @@ public int getBlockHeightOfLastBlock() {
     }
 
     public Optional<AccountingBlock> getLastBlock() {
-        return getBlocks().stream().max(Comparator.comparing(AccountingBlock::getHeight));
+        return StreamSupport.stream(getBlocks().spliterator(), false)
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .max(Comparator.comparing(AccountingBlock::getHeight));
     }
 
     public Optional<AccountingBlock> getBlockAtHeight(int height) {
-        return getBlocks().stream().filter(block -> block.getHeight() == height).findAny();
+        return StreamSupport.stream(getBlocks().spliterator(), false)
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .filter(block -> block.getHeight() == height)
+                .findAny();
     }
 
     public Map<Date, Price> getAverageBsqPriceByMonth() {
@@ -213,8 +222,8 @@ private Stream<ReceivedBtcBalanceEntry> getReceivedBtcBalanceEntryStreamExcludin
     // Delegates
     ///////////////////////////////////////////////////////////////////////////////////////////
 
-    public List<AccountingBlock> getBlocks() {
-        return burningManAccountingStoreService.getBlocks();
+    public Iterable<Optional<AccountingBlock>> getBlocks() {
+        return burningManAccountingStoreService.getAccountingBlockIterable();
     }
 
     public Map<String, String> getBurningManNameByAddress() {

core/src/main/java/bisq/core/dao/burningman/accounting/node/full/network/GetAccountingBlocksRequestHandler.java

@@ -38,8 +38,10 @@
 import com.google.common.util.concurrent.SettableFuture;
 
 import java.util.List;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
+import java.util.stream.StreamSupport;
 
 import lombok.extern.slf4j.Slf4j;
 
@@ -92,7 +94,9 @@ public interface Listener {
 
     public void onGetBlocksRequest(GetAccountingBlocksRequest request, Connection connection) {
         long ts = System.currentTimeMillis();
-        List<AccountingBlock> blocks = burningManAccountingService.getBlocks().stream()
+        List<AccountingBlock> blocks = StreamSupport.stream(burningManAccountingService.getBlocks().spliterator(), false)
+                .filter(Optional::isPresent)
+                .map(Optional::get)
                 .filter(block -> block.getHeight() >= request.getFromBlockHeight())
                 .collect(Collectors.toList());
         byte[] signature = AccountingNode.getSignature(AccountingNode.getSha256Hash(blocks), bmOracleNodePrivKey);

core/src/main/java/bisq/core/dao/burningman/accounting/storage/AccountingBlockIterator.java

@@ -0,0 +1,65 @@
+/*
+ * This file is part of Bisq.
+ *
+ * Bisq is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Bisq is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Bisq. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package bisq.core.dao.burningman.accounting.storage;
+
+import bisq.core.dao.burningman.accounting.blockchain.AccountingBlock;
+
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.Optional;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.Lock;
+
+public class AccountingBlockIterator implements Iterator<Optional<AccountingBlock>> {
+
+    private final Lock readLock;
+    private final LinkedList<AccountingBlock> blocks;
+    private AtomicInteger currentIndex = new AtomicInteger(0);
+
+    public AccountingBlockIterator(Lock readLock, LinkedList<AccountingBlock> blocks) {
+        this.readLock = readLock;
+        this.blocks = blocks;
+    }
+
+    @Override
+    public boolean hasNext() {
+        readLock.lock();
+        try {
+            return currentIndex.get() < blocks.size() - 1;
+        } finally {
+            readLock.unlock();
+        }
+    }
+
+    @Override
+    public Optional<AccountingBlock> next() {
+        readLock.lock();
+        try {
+            if (currentIndex.get() < blocks.size() - 1) {
+                int i = currentIndex.getAndIncrement();
+                AccountingBlock accountingBlock = blocks.get(i);
+                return Optional.of(accountingBlock);
+
+            } else {
+                return Optional.empty();
+            }
+        } finally {
+            readLock.unlock();
+        }
+    }
+}

core/src/main/java/bisq/core/dao/burningman/accounting/storage/BurningManAccountingStore.java

@@ -24,22 +24,75 @@
 
 import com.google.protobuf.Message;
 
+import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.stream.Collectors;
 
-import lombok.Getter;
 import lombok.extern.slf4j.Slf4j;
 
+import org.jetbrains.annotations.NotNull;
+
 @Slf4j
-@Getter
-public class BurningManAccountingStore implements PersistableEnvelope {
+public class BurningManAccountingStore implements PersistableEnvelope, Iterable<Optional<AccountingBlock>> {
+    private final ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
     private final LinkedList<AccountingBlock> blocks = new LinkedList<>();
 
     public BurningManAccountingStore(List<AccountingBlock> blocks) {
         this.blocks.addAll(blocks);
     }
 
+    public void addBlock(AccountingBlock accountingBlock) {
+        Lock writeLock = readWriteLock.writeLock();
+        writeLock.lock();
+        try {
+            blocks.add(accountingBlock);
+        } finally {
+            writeLock.unlock();
+        }
+    }
+
+    public void purgeLastTenBlocks() {
+        Lock writeLock = readWriteLock.writeLock();
+        writeLock.lock();
+        try {
+            purgeLast10Blocks();
+        } finally {
+            writeLock.unlock();
+        }
+    }
+
+    public boolean containsBlock(AccountingBlock block) {
+        Lock readLock = readWriteLock.readLock();
+        try {
+            return blocks.contains(block);
+        } finally {
+            readLock.unlock();
+        }
+    }
+
+    @NotNull
+    @Override
+    public Iterator<Optional<AccountingBlock>> iterator() {
+        Lock readLock = readWriteLock.readLock();
+        return new AccountingBlockIterator(readLock, blocks);
+    }
+
+    private void purgeLast10Blocks() {
+        if (blocks.size() <= 10) {
+            blocks.clear();
+            return;
+        }
+
+        List<AccountingBlock> purged = new ArrayList<>(blocks.subList(0, blocks.size() - 10));
+        blocks.clear();
+        blocks.addAll(purged);
+    }
+
     public Message toProtoMessage() {
         return protobuf.PersistableEnvelope.newBuilder()
                 .setBurningManAccountingStore(protobuf.BurningManAccountingStore.newBuilder()

core/src/main/java/bisq/core/dao/burningman/accounting/storage/BurningManAccountingStoreService.java

@@ -32,8 +32,7 @@
 import java.io.File;
 
 import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
+import java.util.Optional;
 
 import lombok.extern.slf4j.Slf4j;
 
@@ -60,29 +59,24 @@ public void requestPersistence() {
         persistenceManager.requestPersistence();
     }
 
-    public List<AccountingBlock> getBlocks() {
-        return Collections.unmodifiableList(store.getBlocks());
-    }
-
     public void addBlock(AccountingBlock block) {
-        store.getBlocks().add(block);
+        store.addBlock(block);
         requestPersistence();
     }
 
     public void purgeLastTenBlocks() {
-        List<AccountingBlock> blocks = store.getBlocks();
-        if (blocks.size() <= 10) {
-            blocks.clear();
-            requestPersistence();
-            return;
-        }
-
-        List<AccountingBlock> purged = new ArrayList<>(blocks.subList(0, blocks.size() - 10));
-        blocks.clear();
-        blocks.addAll(purged);
+        store.purgeLastTenBlocks();
         requestPersistence();
     }
 
+    public boolean containsAccountingBlock(AccountingBlock block) {
+        return store.containsBlock(block);
+    }
+
+    public Iterable<Optional<AccountingBlock>> getAccountingBlockIterable() {
+        return store;
+    }
+
 
     ///////////////////////////////////////////////////////////////////////////////////////////
     // Protected