Fix pg_atomic_u64 initialization.

hlinnaka · hlinnaka · commit dcd052c8d20c · 2017-08-17T00:48:44.000+03:00
As Andres pointed out, pg_atomic_init_u64 must be used to initialize an atomic variable, before it can be accessed with the actual atomic ops. Trying to use pg_atomic_write_u64 on an uninitialized variable leads to a failure with the fallback implementation that uses a spinlock. Discussion: https://www.postgresql.org/message-id/20170816191346.d3ke5tpshhco4bnd%40alap3.anarazel.de
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -1638,7 +1638,7 @@ heap_parallelscan_initialize(ParallelHeapScanDesc target, Relation relation,
 		target->phs_nblocks > NBuffers / 4;
 	SpinLockInit(&target->phs_mutex);
 	target->phs_startblock = InvalidBlockNumber;
-	pg_atomic_write_u64(&target->phs_nallocated, 0);
+	pg_atomic_init_u64(&target->phs_nallocated, 0);
 	SerializeSnapshot(snapshot, target->phs_snapshot_data);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -1638,7 +1638,7 @@ heap_parallelscan_initialize(ParallelHeapScanDesc target, Relation relation,`
`1638`	`1638`	`target->phs_nblocks > NBuffers / 4;`
`1639`	`1639`	`SpinLockInit(&target->phs_mutex);`
`1640`	`1640`	`target->phs_startblock = InvalidBlockNumber;`
`1641`		`- pg_atomic_write_u64(&target->phs_nallocated, 0);`
	`1641`	`+ pg_atomic_init_u64(&target->phs_nallocated, 0);`
`1642`	`1642`	`SerializeSnapshot(snapshot, target->phs_snapshot_data);`
`1643`	`1643`	`}`
`1644`	`1644`