From c958e7764bab699d77d69c1bf476267b8913a0a9 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Thu, 14 Jul 2016 16:29:21 -0700
Subject: [PATCH] Make pre-commit DB callbacks more atomic with multi-DB
 updates

Bug: T119736
Change-Id: I141903145aae0f6874f4e631624e52b6b9d8a4c8
---
 includes/db/Database.php                  |  4 +++-
 includes/db/loadbalancer/LBFactory.php    |  4 ++++
 includes/db/loadbalancer/LoadBalancer.php | 22 ++++++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/includes/db/Database.php b/includes/db/Database.php
index cfdf3828d1..147bf27c13 100644
--- a/includes/db/Database.php
+++ b/includes/db/Database.php
@@ -2520,9 +2520,11 @@ abstract class DatabaseBase implements IDatabase {
 	/**
 	 * Actually any "on transaction pre-commit" callbacks.
 	 *
+	 * This method should not be used outside of Database/LoadBalancer
+	 *
 	 * @since 1.22
 	 */
-	protected function runOnTransactionPreCommitCallbacks() {
+	public function runOnTransactionPreCommitCallbacks() {
 		$e = $ePrior = null; // last exception
 		do { // callbacks may add callbacks :)
 			$callbacks = $this->mTrxPreCommitCallbacks;
diff --git a/includes/db/loadbalancer/LBFactory.php b/includes/db/loadbalancer/LBFactory.php
index 5b048b53d8..9a1d679550 100644
--- a/includes/db/loadbalancer/LBFactory.php
+++ b/includes/db/loadbalancer/LBFactory.php
@@ -224,6 +224,10 @@ abstract class LBFactory implements DestructibleService {
 	public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
 		$limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
 
+		// Run pre-commit callbacks to keep them out of the COMMIT step. If one errors out here
+		// then all DB transactions can be rolled back before anything was committed yet.
+		$this->forEachLBCallMethod( 'runPreCommitCallbacks' );
+
 		$this->logMultiDbTransaction();
 		$this->forEachLB( function ( LoadBalancer $lb ) use ( $limit ) {
 			$lb->forEachOpenConnection( function ( IDatabase $db ) use ( $limit ) {
diff --git a/includes/db/loadbalancer/LoadBalancer.php b/includes/db/loadbalancer/LoadBalancer.php
index d96c665e4f..d9a7381516 100644
--- a/includes/db/loadbalancer/LoadBalancer.php
+++ b/includes/db/loadbalancer/LoadBalancer.php
@@ -1115,6 +1115,28 @@ class LoadBalancer {
 		}
 	}
 
+	/**
+	 * Call runOnTransactionPreCommitCallbacks() on all DB handles
+	 *
+	 * This method should not be used outside of LBFactory/LoadBalancer
+	 *
+	 * @since 1.28
+	 */
+	public function runPreCommitCallbacks() {
+		$masterIndex = $this->getWriterIndex();
+		foreach ( $this->mConns as $conns2 ) {
+			if ( empty( $conns2[$masterIndex] ) ) {
+				continue;
+			}
+			/** @var DatabaseBase $conn */
+			foreach ( $conns2[$masterIndex] as $conn ) {
+				if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
+					$conn->runOnTransactionPreCommitCallbacks();
+				}
+			}
+		}
+	}
+
 	/**
 	 * @return bool Whether a master connection is already open
 	 * @since 1.24
-- 
2.20.1