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Fix race condition in LocalAuctionClusterBridge lock implementation #12

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Fix race condition in LocalAuctionClusterBridge lock implementation #12

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5a5e86e
Update LocalAuctionClusterBridge.java
hanaemercier Jan 6, 2026
f91892c
Update PurchaseService.java
hanaemercier Jan 6, 2026
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12 changes: 11 additions & 1 deletion src/main/java/fr/maxlego08/zauctionhouse/cluster/LocalAuctionClusterBridge.java
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Original file line number Diff line number Diff line change
Expand Up @@ -9,21 +9,31 @@

import java.util.UUID;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;

public class LocalAuctionClusterBridge implements AuctionClusterBridge {

private final ConcurrentHashMap<UUID, UUID> itemLocks = new ConcurrentHashMap<>();
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Copilot AI Jan 8, 2026

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The ConcurrentHashMap is using UUID as the key type, but item.getId() returns an int. This causes a type mismatch that will result in a compilation error. The map should be declared as ConcurrentHashMap<Integer, UUID> to match the item ID type.

Suggested change
private final ConcurrentHashMap<UUID, UUID> itemLocks = new ConcurrentHashMap<>();
private final ConcurrentHashMap<Integer, UUID> itemLocks = new ConcurrentHashMap<>();

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@Override
public CompletableFuture<Boolean> checkAvailability(Item item) {
return CompletableFuture.completedFuture(true);
return CompletableFuture.completedFuture(!itemLocks.containsKey(item.getId()));
}

@Override
public CompletableFuture<LockToken> lockItem(Item item, UUID buyerId, StorageType storageType) {
UUID existingLock = itemLocks.putIfAbsent(item.getId(), buyerId);

if (existingLock != null) {
return CompletableFuture.failedFuture(new IllegalStateException("Item already locked by another player"));
}

return CompletableFuture.completedFuture(LockToken.of(item));
}

@Override
public CompletableFuture<Void> unlockItem(Item item, LockToken lockToken, StorageType storageType) {
itemLocks.remove(item.getId());
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The unlockItem method does not verify that the caller actually owns the lock before removing it. Any code with any LockToken can unlock an item, even if it was locked by a different buyer. This could allow malicious code or bugs to unlock items they don't own. Consider verifying that the buyerId matches the stored lock owner before allowing the unlock operation.

Suggested change
itemLocks.remove(item.getId());
UUID currentOwner = itemLocks.get(item.getId());
// If there is no current lock, consider it already unlocked.
if (currentOwner == null) {
return CompletableFuture.completedFuture(null);
}
// Verify that the lock token belongs to the current owner before unlocking.
UUID tokenBuyerId = lockToken.getBuyerId();
if (!currentOwner.equals(tokenBuyerId)) {
return CompletableFuture.failedFuture(
new IllegalStateException("Lock token does not match the current lock owner"));
}
itemLocks.remove(item.getId(), currentOwner);

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Actual argument type 'Integer' is incompatible with expected argument type 'UUID'.

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return CompletableFuture.completedFuture(null);
}

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15 changes: 8 additions & 7 deletions src/main/java/fr/maxlego08/zauctionhouse/services/PurchaseService.java
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Expand Up @@ -46,15 +46,16 @@ public CompletableFuture<Void> purchaseItem(Player player, Item item) {
auctionManager.openMainAuction(player);
return CompletableFuture.completedFuture(null);
}

if (item.getStatus() != ItemStatus.IS_PURCHASE_CONFIRM) {
logger.info("Item not available");
auctionManager.openMainAuction(player);
return CompletableFuture.completedFuture(null);

synchronized(item) {
if (item.getStatus() != ItemStatus.IS_PURCHASE_CONFIRM) {
logger.info("Item not available");
auctionManager.openMainAuction(player);
return CompletableFuture.completedFuture(null);
}
item.setStatus(ItemStatus.IS_BEING_PURCHASED);
}
Comment on lines +50 to 57
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The status check and status change are wrapped in a synchronized block, but this doesn't prevent race conditions when different threads have different Item object instances representing the same database record. Two threads could each have their own Item instance (same ID but different objects), pass the status check, and both set the status to IS_BEING_PURCHASED. The synchronized block only works if all threads use the exact same object instance, which is not guaranteed in a distributed or multi-request scenario.

Suggested change
synchronized(item) {
if (item.getStatus() != ItemStatus.IS_PURCHASE_CONFIRM) {
logger.info("Item not available");
auctionManager.openMainAuction(player);
return CompletableFuture.completedFuture(null);
}
item.setStatus(ItemStatus.IS_BEING_PURCHASED);
}
if (item.getStatus() != ItemStatus.IS_PURCHASE_CONFIRM) {
logger.info("Item not available");
auctionManager.openMainAuction(player);
return CompletableFuture.completedFuture(null);
}
item.setStatus(ItemStatus.IS_BEING_PURCHASED);

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item.setStatus(ItemStatus.IS_BEING_PURCHASED);

// 2. Vérifier si l'item est lock
return clusterBridge.checkAvailability(item).thenCompose(available -> {

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