SERVER-40301 Don't hold mutex while doing queries in nextCloneBatch and nextModsBatch

1 files changed, 22 insertions, 17 deletions

diff --git a/src/mongo/db/s/migration_chunk_cloner_source_legacy.h b/src/mongo/db/s/migration_chunk_cloner_source_legacy.h
index 3874f03e76a..1fd34944a8b 100644
--- a/src/mongo/db/s/migration_chunk_cloner_source_legacy.h
+++ b/src/mongo/db/s/migration_chunk_cloner_source_legacy.h
@@ -120,7 +120,8 @@ public:
 
     /**
      * Called by the recipient shard. Populates the passed BSONArrayBuilder with a set of documents,
-     * which are part of the initial clone sequence.
+     * which are part of the initial clone sequence. Assumes that there is only one active caller
+     * to this method at a time (otherwise, it can cause corruption/crash).
      *
      * Returns OK status on success. If there were documents returned in the result argument, this
      * method should be called more times until the result is empty. If it returns failure, it is
@@ -201,22 +202,6 @@ private:
      */
     Status _storeCurrentLocs(OperationContext* opCtx);
 
-    /**
-     * Insert items from docIdList to a new array with the given fieldName in the given builder. If
-     * explode is true, the inserted object will be the full version of the document. Note that
-     * whenever an item from the docList is inserted to the array, it will also be removed from
-     * docList.
-     *
-     * Should be holding the collection lock for ns if explode is true.
-     */
-    void _xfer(OperationContext* opCtx,
-               Database* db,
-               std::list<BSONObj>* docIdList,
-               BSONObjBuilder* builder,
-               const char* fieldName,
-               long long* sizeAccumulator,
-               bool explode);
-
     /*
      * Consumes the operation track request and appends the relevant document changes to
      * the appropriate internal data structures (known colloquially as the 'transfer mods queue').
@@ -266,6 +251,26 @@ private:
      */
     void _drainAllOutstandingOperationTrackRequests(stdx::unique_lock<stdx::mutex>& lk);
 
+    /**
+     * Appends to the builder the list of _id of documents that were deleted during migration.
+     * Entries appended to the builder are removed from the list.
+     * Returns the total size of the documents that were appended + initialSize.
+     */
+    long long _xferDeletes(BSONObjBuilder* builder,
+                           std::list<BSONObj>* removeList,
+                           long long initialSize);
+
+    /**
+     * Appends to the builder the list of full documents that were modified/inserted during the
+     * migration. Entries appended to the builder are removed from the list.
+     * Returns the total size of the documents that were appended + initialSize.
+     */
+    long long _xferUpdates(OperationContext* opCtx,
+                           Database* db,
+                           BSONObjBuilder* builder,
+                           std::list<BSONObj>* updateList,
+                           long long initialSize);
+
     // The original move chunk request
     const MoveChunkRequest _args;