X-Git-Url: http://git.cyclocoop.org/?a=blobdiff_plain;f=includes%2Fdao%2FIDBAccessObject.php;h=3690735ed5bb4b482888a491408c8ea742cf16ac;hb=8006aa946aaf1ef948323f4b717c0359f60f1c2e;hp=e30522a5526b5d0c3df9b44820ebcb5b51fb4467;hpb=ddfce8feb06afe46bfa778be27c5b5b369861f5e;p=lhc%2Fweb%2Fwiklou.git

diff --git a/includes/dao/IDBAccessObject.php b/includes/dao/IDBAccessObject.php
index e30522a552..3690735ed5 100644
--- a/includes/dao/IDBAccessObject.php
+++ b/includes/dao/IDBAccessObject.php
@@ -28,10 +28,12 @@
  * functions. In general, objects should assume READ_NORMAL if no flags are explicitly given,
  * though certain objects may assume READ_LATEST for common use case or legacy reasons.
  *
- * There are three types of reads:
- *   - READ_NORMAL  : Potentially cached read of data (e.g. from a slave or stale replica)
- *   - READ_LATEST  : Up-to-date read as of transaction start (e.g. from master or a quorum read)
- *   - READ_LOCKING : Up-to-date read as of now, that locks the records for the transaction
+ * There are four types of reads:
+ *   - READ_NORMAL    : Potentially cached read of data (e.g. from a slave or stale replica)
+ *   - READ_LATEST    : Up-to-date read as of transaction start (e.g. from master or a quorum read)
+ *   - READ_LOCKING   : Up-to-date read as of now, that locks (shared) the records
+ *   - READ_EXCLUSIVE : Up-to-date read as of now, that locks (exclusive) the records
+ * All record locks persist for the duration of the transaction.
  *
  * Callers should use READ_NORMAL (or pass in no flags) unless the read determines a write.
  * In theory, such cases may require READ_LOCKING, though to avoid contention, READ_LATEST is
@@ -41,11 +43,14 @@
  *   - b) Determine the new row (expensive, so we don't want to hold locks now)
  *   - c) Re-read the current row with READ_LOCKING; if it changed then bail out
  *   - d) otherwise, do the updates
+ *
+ * @since 1.20
  */
 interface IDBAccessObject {
 	// Constants for object loading bitfield flags (higher => higher QoS)
-	const READ_LATEST  = 1; // read from the master
-	const READ_LOCKING = 3; // READ_LATEST and "FOR UPDATE"
+	const READ_LATEST = 1; // read from the master
+	const READ_LOCKING = 3; // READ_LATEST (1) and "LOCK IN SHARE MODE" (2)
+	const READ_EXCLUSIVE = 7; // READ_LOCKING (3) and "FOR UPDATE" (4)
 
 	// Convenience constant for callers to explicitly request slave data
 	const READ_NORMAL = 0; // read from the slave