From 4d7f18f6d5b9e96aabee4646e7c7a63834c3d223 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Tue, 1 Apr 2014 13:25:42 -0700
Subject: [PATCH] Made BagOStuff fail fast in cas/lock on certain errors

* This avoids wasting time waiting on down servers

bug: 63058
Change-Id: Ia78a2036ffa7a20102ec9e8bf941cacb7fa63435
---
 includes/objectcache/BagOStuff.php            | 41 +++++++++++++++++++
 .../objectcache/MemcachedPeclBagOStuff.php    |  1 +
 includes/objectcache/MultiWriteBagOStuff.php  | 10 +++++
 includes/objectcache/RedisBagOStuff.php       |  2 +
 includes/objectcache/SqlBagOStuff.php         |  4 ++
 5 files changed, 58 insertions(+)

diff --git a/includes/objectcache/BagOStuff.php b/includes/objectcache/BagOStuff.php
index 217142c0b4..ad3aa96201 100644
--- a/includes/objectcache/BagOStuff.php
+++ b/includes/objectcache/BagOStuff.php
@@ -43,6 +43,14 @@
 abstract class BagOStuff {
 	private $debugMode = false;
 
+	protected $lastError = self::ERR_NONE;
+
+	/** Possible values for getLastError() */
+	const ERR_NONE        = 0; // no error
+	const ERR_NO_RESPONSE = 1; // no response
+	const ERR_UNREACHABLE = 2; // can't connect
+	const ERR_UNEXPECTED  = 3; // response gave some error
+
 	/**
 	 * @param $bool bool
 	 */
@@ -169,9 +177,12 @@ abstract class BagOStuff {
 	 * @return bool success
 	 */
 	public function lock( $key, $timeout = 6 ) {
+		$this->clearLastError();
 		$timestamp = microtime( true ); // starting UNIX timestamp
 		if ( $this->add( "{$key}:lock", 1, $timeout ) ) {
 			return true;
+		} elseif ( $this->getLastError() ) {
+			return false;
 		}
 
 		$uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
@@ -186,7 +197,11 @@ abstract class BagOStuff {
 				$sleep *= 2;
 			}
 			usleep( $sleep ); // back off
+			$this->clearLastError();
 			$locked = $this->add( "{$key}:lock", 1, $timeout );
+			if ( $this->getLastError() ) {
+				return false;
+			}
 		} while ( !$locked );
 
 		return $locked;
@@ -292,6 +307,32 @@ abstract class BagOStuff {
 		return $this->incr( $key, - $value );
 	}
 
+	/**
+	 * Get the "last error" registered; clearLastError() should be called manually
+	 * @return integer ERR_* constant for the "last error" registry
+	 * @since 1.23
+	 */
+	public function getLastError() {
+		return $this->lastError;
+	}
+
+	/**
+	 * Clear the "last error" registry
+	 * @since 1.23
+	 */
+	public function clearLastError() {
+		$this->lastError = self::ERR_NONE;
+	}
+
+	/**
+	 * Set the "last error" registry
+	 * @param $err integer ERR_* constant
+	 * @since 1.23
+	 */
+	protected function setLastError( $err ) {
+		$this->lastError = $err;
+	}
+
 	/**
 	 * @param $text string
 	 */
diff --git a/includes/objectcache/MemcachedPeclBagOStuff.php b/includes/objectcache/MemcachedPeclBagOStuff.php
index 18546d4049..1c780b4788 100644
--- a/includes/objectcache/MemcachedPeclBagOStuff.php
+++ b/includes/objectcache/MemcachedPeclBagOStuff.php
@@ -231,6 +231,7 @@ class MemcachedPeclBagOStuff extends MemcachedBagOStuff {
 					$msg = "Memcached error: $msg";
 				}
 				wfDebugLog( 'memcached-serious', $msg );
+				$this->setLastError( BagOStuff::ERR_UNEXPECTED );
 		}
 		return $result;
 	}
diff --git a/includes/objectcache/MultiWriteBagOStuff.php b/includes/objectcache/MultiWriteBagOStuff.php
index e550c0d0e4..b97410a5cc 100644
--- a/includes/objectcache/MultiWriteBagOStuff.php
+++ b/includes/objectcache/MultiWriteBagOStuff.php
@@ -179,6 +179,16 @@ class MultiWriteBagOStuff extends BagOStuff {
 		return $this->doWrite( 'merge', $key, $callback, $exptime );
 	}
 
+	public function getLastError() {
+		return isset( $this->caches[0] ) ? $this->caches[0]->getLastError() : self::ERR_NONE;
+	}
+
+	public function clearLastError() {
+		if ( isset( $this->caches[0] ) ) {
+			$this->caches[0]->clearLastError();
+		}
+	}
+
 	/**
 	 * @param $method string
 	 * @return bool
diff --git a/includes/objectcache/RedisBagOStuff.php b/includes/objectcache/RedisBagOStuff.php
index f54726f159..872af638ae 100644
--- a/includes/objectcache/RedisBagOStuff.php
+++ b/includes/objectcache/RedisBagOStuff.php
@@ -305,6 +305,7 @@ class RedisBagOStuff extends BagOStuff {
 				return array( $server, $conn );
 			}
 		}
+		$this->setLastError( BagOStuff::ERR_UNREACHABLE );
 		return array( false, false );
 	}
 
@@ -322,6 +323,7 @@ class RedisBagOStuff extends BagOStuff {
 	 * object and let it be reopened during the next request.
 	 */
 	protected function handleException( RedisConnRef $conn, $e ) {
+		$this->setLastError( BagOStuff::ERR_UNEXPECTED );
 		$this->redisPool->handleError( $conn, $e );
 	}
 
diff --git a/includes/objectcache/SqlBagOStuff.php b/includes/objectcache/SqlBagOStuff.php
index 2c90339aed..74b5de259e 100644
--- a/includes/objectcache/SqlBagOStuff.php
+++ b/includes/objectcache/SqlBagOStuff.php
@@ -626,8 +626,10 @@ class SqlBagOStuff extends BagOStuff {
 		}
 		wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 		if ( $exception instanceof DBConnectionError ) {
+			$this->setLastError( BagOStuff::ERR_UNREACHABLE );
 			wfDebug( __METHOD__ . ": ignoring connection error\n" );
 		} else {
+			$this->setLastError( BagOStuff::ERR_UNEXPECTED );
 			wfDebug( __METHOD__ . ": ignoring query error\n" );
 		}
 	}
@@ -646,8 +648,10 @@ class SqlBagOStuff extends BagOStuff {
 		}
 		wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 		if ( $exception instanceof DBConnectionError ) {
+			$this->setLastError( BagOStuff::ERR_UNREACHABLE );
 			wfDebug( __METHOD__ . ": ignoring connection error\n" );
 		} else {
+			$this->setLastError( BagOStuff::ERR_UNEXPECTED );
 			wfDebug( __METHOD__ . ": ignoring query error\n" );
 		}
 	}
-- 
2.20.1