SERVER-50984 Add CollectionPtr to replace usage of const Collection*

It implements a yieldable interface that is used to re-load the
Collection pointer from the catalog after a yield that released locks.
With lock-free reads and copy-on-write on Collection instances releasing
locks without notifying an AutoGetCollection at a higher level may cause
its pointers to dangle if a MODE_X writer installs a new Collection
instance in the catalog.

CollectionPtr should be passed by const reference so a yield can notify
all the way up.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/mongo/db/s/shard_local.cpp b/src/mongo/db/s/shard_local.cpp
index 9b432100426..8b293435bfb 100644
--- a/src/mongo/db/s/shard_local.cpp
+++ b/src/mongo/db/s/shard_local.cpp
@@ -127,9 +127,11 @@ Status ShardLocal::createIndexOnConfig(OperationContext* opCtx,
     invariant(ns.db() == "config" || ns.db() == "admin");
 
     try {
+        // TODO SERVER-50983: Create abstraction for creating collection when using
+        // AutoGetCollection
         AutoGetOrCreateDb autoDb(opCtx, ns.db(), MODE_IX);
         AutoGetCollection autoColl(opCtx, ns, MODE_X);
-        auto collection = autoColl.getCollection();
+        const Collection* collection = autoColl.getCollection().get();
         if (!collection) {
             CollectionOptions options;
             options.uuid = UUID::gen();