R3944Realms/PlayerSync
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Phase 18.1: fix CAS kicking first-time players

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Regression from Phase 15: new players connecting for the FIRST time got
kicked with 'PlayerSync: another server is finalizing your save. Please
reconnect in a few seconds.' before they ever saw the world.

Root cause: the Phase 15 atomic CAS was
    UPDATE player_data SET last_server=?, online=1, logout_started_at=NULL
    WHERE uuid=? AND (online=0 OR last_server=?)
For a brand-new player the player_data row does not exist yet — the WHERE
clause matches zero rows and executePreparedUpdateRet returns 0. The
surrounding check treated 'claim == 0' as 'another server beat us', so
it kicked the player. But it was really 'no row to update yet' — the
store(player, true) call further down the flow is what INSERTs the row.

Fix: the poll loop already detects row-missing via rsCheck.next() == false
and breaks out. Thread that signal through as isNewPlayer and skip the
CAS entirely when it's set. The subsequent !playerExists branch picks up
the new player and INSERTs the row with the correct state.

No impact on the cross-server race safety: existing-row players still run
the full CAS; only the true-first-connection path is unblocked. Zero risk
of duplication / data loss — new players have nothing to duplicate or lose.
This commit is contained in:
laforetbrut 2026-04-22 19:22:34 +02:00
parent 2347c62298
commit 6c986faa3f
1 changed files with 49 additions and 31 deletions
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80
src/main/java/vip/fubuki/playersync/sync/VanillaSync.java
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@ -464,6 +464,13 @@ public class VanillaSync {
final int SELF = JdbcConfig.SERVER_ID.get();
boolean forceClaim = false; // bypass online=0 / last_server=self guard
// PHASE 18.1 FIX: track whether the row exists at all. A brand-new player
// has no row yet — the CAS claim below must be skipped (it would return
// 0 rows affected, which the old code misinterpreted as 'another server
// claimed first' and wrongly kicked the player with the 'finalizing your
// save' message on their very first connection). For new players the row
// gets INSERTed later by store(player, true) in the new-player branch.
boolean isNewPlayer = false;
final long pollStartTime = System.currentTimeMillis();
for (int attempt = 0; attempt < MAX_POLL; attempt++) {
int otherServer;
@ -476,7 +483,10 @@ public class VanillaSync {
+ Tables.playerData() + " WHERE uuid=?", player_uuid)) {
ResultSet rsCheck = qrCheck.resultSet();
rowExists = rsCheck.next();
if (!rowExists) break; // new player — nothing to wait for
if (!rowExists) {
isNewPlayer = true;
break; // new player — nothing to wait for, skip CAS
}
otherServer = rsCheck.getInt("last_server");
otherOnline = rsCheck.getBoolean("online");
logoutStartedAt = rsCheck.getLong("lsa");
@ -543,37 +553,45 @@ public class VanillaSync {
// CLAIM with atomic CAS. Two concurrent joining servers can never
// both succeed — the one that lands its UPDATE second sees 0 rows
// affected and aborts its restore.
//
// PHASE 18.1: new players skip the CAS entirely. No row exists yet,
// so UPDATE affects 0 rows by definition — the old code was kicking
// FIRST-TIME joiners with "another server is finalizing your save".
// store() in the new-player branch will INSERT the row with the
// correct state in a moment.
// ================================================================
int claimed;
if (forceClaim) {
// Unconditional — we've decided the previous owner is defunct.
claimed = JDBCsetUp.executePreparedUpdateRet(
"UPDATE " + Tables.playerData()
+ " SET last_server=?, online=1, logout_started_at=NULL WHERE uuid=?",
SELF, player_uuid);
} else {
// Guarded — only claim if the row is actually clean or already ours.
claimed = JDBCsetUp.executePreparedUpdateRet(
"UPDATE " + Tables.playerData()
+ " SET last_server=?, online=1, logout_started_at=NULL"
+ " WHERE uuid=? AND (online=0 OR last_server=?)",
SELF, player_uuid, SELF);
}
if (claimed == 0) {
// Another server beat us to it (or the row disappeared).
// Refuse to overwrite its data — kick ourselves and let the
// player reconnect; state will be consistent by then.
PlayerSync.LOGGER.warn("Player {} claim CAS lost — another server claimed first; kicking this session", player_uuid);
SyncLogger.raceCondition(player_uuid, "Claim CAS lost — deferring to the winner");
server.execute(() -> {
if (serverPlayer.connection != null) {
serverPlayer.connection.disconnect(Component.translatableWithFallback(
"playersync.claim_lost",
"PlayerSync: another server is finalizing your save. Please reconnect in a few seconds."));
}
});
syncNotCompletedPlayer.remove(player_uuid);
return;
if (!isNewPlayer) {
int claimed;
if (forceClaim) {
// Unconditional — we've decided the previous owner is defunct.
claimed = JDBCsetUp.executePreparedUpdateRet(
"UPDATE " + Tables.playerData()
+ " SET last_server=?, online=1, logout_started_at=NULL WHERE uuid=?",
SELF, player_uuid);
} else {
// Guarded — only claim if the row is actually clean or already ours.
claimed = JDBCsetUp.executePreparedUpdateRet(
"UPDATE " + Tables.playerData()
+ " SET last_server=?, online=1, logout_started_at=NULL"
+ " WHERE uuid=? AND (online=0 OR last_server=?)",
SELF, player_uuid, SELF);
}
if (claimed == 0) {
// Row exists (we checked in the poll) but the guard blocked us —
// meaning another server claimed between our poll read and our
// UPDATE. Defer to that winner and ask the player to retry.
PlayerSync.LOGGER.warn("Player {} claim CAS lost — another server claimed first; kicking this session", player_uuid);
SyncLogger.raceCondition(player_uuid, "Claim CAS lost — deferring to the winner");
server.execute(() -> {
if (serverPlayer.connection != null) {
serverPlayer.connection.disconnect(Component.translatableWithFallback(
"playersync.claim_lost",
"PlayerSync: another server is finalizing your save. Please reconnect in a few seconds."));
}
});
syncNotCompletedPlayer.remove(player_uuid);
return;
}
}
// === PHASE 1: DB reads on background thread (thread-safe) ===