[2/3] incubator-kudu git commit: KUDU-1491. Address TSAN warning for compaction

[to...@apache.org]

KUDU-1491. Address TSAN warning for compaction

This adds a missing memory barrier that was exposed when I removed
TSAN suppressions for mutation lists. Without the patch, TSAN
failed on mt-tablet-test a few percent of the time. With the patch,
I looped it 50 times with no failures:

http://dist-test.cloudera.org/job?job_id=todd.1466638821.4940

Change-Id: I42d2566eca096da172440ce3a88d0393dda9d324
Reviewed-on: http://gerrit.cloudera.org:8080/3454
Reviewed-by: Adar Dembo <ad...@cloudera.com>
Tested-by: Kudu Jenkins


Project: http://git-wip-us.apache.org/repos/asf/incubator-kudu/repo
Commit: http://git-wip-us.apache.org/repos/asf/incubator-kudu/commit/19e78f72
Tree: http://git-wip-us.apache.org/repos/asf/incubator-kudu/tree/19e78f72
Diff: http://git-wip-us.apache.org/repos/asf/incubator-kudu/diff/19e78f72

Branch: refs/heads/master
Commit: 19e78f727fa66316833c513b528f389b006ce419
Parents: 7b280a0
Author: Todd Lipcon <to...@cloudera.com>
Authored: Wed Jun 22 16:41:26 2016 -0700
Committer: Todd Lipcon <to...@apache.org>
Committed: Thu Jun 23 00:47:42 2016 +0000

----------------------------------------------------------------------
 src/kudu/tablet/compaction.cc | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/incubator-kudu/blob/19e78f72/src/kudu/tablet/compaction.cc
----------------------------------------------------------------------
diff --git a/src/kudu/tablet/compaction.cc b/src/kudu/tablet/compaction.cc
index 8f4a131..9243337 100644
--- a/src/kudu/tablet/compaction.cc
+++ b/src/kudu/tablet/compaction.cc
@@ -506,8 +506,9 @@ class MergeCompactionInput : public CompactionInput {
   }
 
   static void AdvanceToLastInList(const Mutation** m) {
-    while ((*m)->next() != nullptr) {
-      *m = (*m)->next();
+    const Mutation* next;
+    while ((next = (*m)->acquire_next()) != nullptr) {
+      *m = next;
     }
   }
 
@@ -883,7 +884,7 @@ Status ReupdateMissedDeltas(const string &tablet_name,
 
       for (const Mutation *mut = row.redo_head;
            mut != nullptr;
-           mut = mut->next()) {
+           mut = mut->acquire_next()) {
         RowChangeListDecoder decoder(mut->changelist());
         RETURN_NOT_OK(decoder.Init());