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, 2 insertions, 2 deletions

diff --git a/src/mongo/db/concurrency/deferred_writer.cpp b/src/mongo/db/concurrency/deferred_writer.cpp
index 3883ae2cd40..6c0f0ed3c77 100644
--- a/src/mongo/db/concurrency/deferred_writer.cpp
+++ b/src/mongo/db/concurrency/deferred_writer.cpp
@@ -112,11 +112,11 @@ void DeferredWriter::_worker(InsertStatement stmt) {
 
     auto agc = std::move(result.getValue());
 
-    const Collection& collection = *agc->getCollection();
+    const CollectionPtr& collection = agc->getCollection();
 
     Status status = writeConflictRetry(opCtx, "deferred insert", _nss.ns(), [&] {
         WriteUnitOfWork wuow(opCtx);
-        Status status = collection.insertDocument(opCtx, stmt, nullptr, false);
+        Status status = collection->insertDocument(opCtx, stmt, nullptr, false);
         if (!status.isOK()) {
             return status;
         }