Don't call OwnLatch while holding a spinlock. OwnLatch can elog() under

hlinnaka · hlinnaka · commit 1eab7a560d09 · 2010-09-15T06:51:19.000Z
some "can't happen" scenarios, and spinlocks should only be held for
a few instructions anyway. As pointed out by Fujii Masao.
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
@@ -28,7 +28,7 @@
  * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.31 2010/09/14 13:35:14 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.32 2010/09/15 06:51:19 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -511,15 +511,15 @@ InitWalSnd(void)
 		else
 		{
 			/*
-			 * Found a free slot. Take ownership of the latch and initialize
-			 * the other fields.
+			 * Found a free slot. Reserve it for us.
 			 */
-			OwnLatch((Latch *) &walsnd->latch);
 			walsnd->pid = MyProcPid;
 			MemSet(&walsnd->sentPtr, 0, sizeof(XLogRecPtr));
-			/* Set MyWalSnd only after it's fully initialized. */
-			MyWalSnd = (WalSnd *) walsnd;
 			SpinLockRelease(&walsnd->mutex);
+			/* don't need the lock anymore */
+			OwnLatch((Latch *) &walsnd->latch);
+			MyWalSnd = (WalSnd *) walsnd;
+
 			break;
 		}
 	}

Original file line number	Diff line number	Diff line change
`@@ -28,7 +28,7 @@`
`28`	`28`	`* Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group`
`29`	`29`	`*`
`30`	`30`	`* IDENTIFICATION`
`31`		`- * $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.31 2010/09/14 13:35:14 heikki Exp $`
	`31`	`+ * $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.32 2010/09/15 06:51:19 heikki Exp $`
`32`	`32`	`*`
`33`	`33`	`*-------------------------------------------------------------------------`
`34`	`34`	`*/`
`@@ -511,15 +511,15 @@ InitWalSnd(void)`
`511`	`511`	`else`
`512`	`512`	`{`
`513`	`513`	`/*`
`514`		`- * Found a free slot. Take ownership of the latch and initialize`
`515`		`- * the other fields.`
	`514`	`+ * Found a free slot. Reserve it for us.`
`516`	`515`	`*/`
`517`		`- OwnLatch((Latch *) &walsnd->latch);`
`518`	`516`	`walsnd->pid = MyProcPid;`
`519`	`517`	`MemSet(&walsnd->sentPtr, 0, sizeof(XLogRecPtr));`
`520`		`- /* Set MyWalSnd only after it's fully initialized. */`
`521`		`- MyWalSnd = (WalSnd *) walsnd;`
`522`	`518`	`SpinLockRelease(&walsnd->mutex);`
	`519`	`+ /* don't need the lock anymore */`
	`520`	`+ OwnLatch((Latch *) &walsnd->latch);`
	`521`	`+ MyWalSnd = (WalSnd *) walsnd;`
	`522`	`+`
`523`	`523`	`break;`
`524`	`524`	`}`
`525`	`525`	`}`