SERVER-15888: Ensure MODE_X on implicit DB creation

Also adds new API to DBLock to allow relocking in different mode.

1 files changed, 103 insertions, 68 deletions

diff --git a/src/mongo/db/client.h b/src/mongo/db/client.h
index 033c6049577..ce2d50717de 100644
--- a/src/mongo/db/client.h
+++ b/src/mongo/db/client.h
@@ -56,11 +56,98 @@ namespace mongo {
     class Collection;
     class AbstractMessagingPort;
 
-
     TSP_DECLARE(Client, currentClient)
 
     typedef long long ConnectionId;
 
+    /**
+     * RAII-style class, which acquires a lock on the specified database in the requested mode and
+     * obtains a reference to the database. Used as a shortcut for calls to dbHolder().get().
+     *
+     * It is guaranteed that locks will be released when this object goes out of scope, therefore
+     * the database reference returned by this class should not be retained.
+     *
+     * TODO: This should be moved outside of client.h (maybe dbhelpers.h)
+     */
+    class AutoGetDb {
+        MONGO_DISALLOW_COPYING(AutoGetDb);
+    public:
+        AutoGetDb(OperationContext* txn, const StringData& ns, LockMode mode);
+
+        Database* getDb() const {
+            return _db;
+        }
+    private:
+        const Lock::DBLock _dbLock;
+        Database* const _db;
+    };
+
+    /**
+     * RAII-style class, which acquires a lock on the specified database in the requested mode and
+     * obtains a reference to the database, creating it was non-existing. Used as a shortcut for
+     * calls to dbHolder().openDb(), taking care of locking details. The requested mode must be
+     * MODE_IX or MODE_X. If the database needs to be created, the lock will automatically be
+     * reacquired as MODE_X.
+     *
+     * It is guaranteed that locks will be released when this object goes out of scope, therefore
+     * the database reference returned by this class should not be retained.
+     *
+     * TODO: This should be moved outside of client.h (maybe dbhelpers.h)
+     */
+    class AutoGetOrCreateDb {
+        MONGO_DISALLOW_COPYING(AutoGetOrCreateDb);
+    public:
+        AutoGetOrCreateDb(OperationContext* txn, const StringData& ns, LockMode mode);
+
+        Database* getDb() {
+            return _db;
+        }
+
+        bool justCreated() {
+            return _justCreated;
+        }
+    private:
+        Lock::DBLock _dbLock; // not const, as we may need to relock for implicit create
+        Database* _db;
+        bool _justCreated;
+    };
+
+    /**
+     * RAII-style class, which would acquire the appropritate hierarchy of locks for obtaining
+     * a particular collection and would retrieve a reference to the collection.
+     *
+     * It is guaranteed that locks will be released when this object goes out of scope, therefore
+     * database and collection references returned by this class should not be retained.
+     *
+     * TODO: This should be moved outside of client.h (maybe dbhelpers.h)
+     */
+    class AutoGetCollectionForRead {
+        MONGO_DISALLOW_COPYING(AutoGetCollectionForRead);
+    public:
+        AutoGetCollectionForRead(OperationContext* txn, const std::string& ns);
+        AutoGetCollectionForRead(OperationContext* txn, const NamespaceString& nss);
+        ~AutoGetCollectionForRead();
+
+        Database* getDb() const {
+            return _db.getDb();
+        }
+
+        Collection* getCollection() const {
+            return _coll;
+        }
+
+    private:
+        void _init();
+
+        const Timer _timer;
+        OperationContext* const _txn;
+        const NamespaceString _nss;
+        const AutoGetDb _db;
+        const Lock::CollectionLock _collLock;
+
+        Collection* _coll;
+    };
+
     /** the database's concept of an outside "client" */
     class Client : public ClientBasic {
     public:
@@ -155,10 +242,20 @@ namespace mongo {
             /** this is probably what you want */
             Context(OperationContext* txn, const std::string& ns, bool doVersion = true);
 
-            /** note: this does not call finishInit -- i.e., does not call 
-                      ensureShardVersionOKOrThrow for example.
-                see also: reset().
-            */
+            /**
+             * Below still calls _finishInit, but assumes database has already been acquired
+             * or just created.
+             */
+            Context(OperationContext* txn,
+                    const std::string& ns,
+                    Database* db,
+                    bool justCreated);
+
+            /**
+             * note: this does not call _finishInit -- i.e., does not call
+             * ensureShardVersionOKOrThrow for example.
+             * see also: reset().
+             */
             Context(OperationContext* txn, const std::string& ns, Database * db);
 
             ~Context();
@@ -209,74 +306,12 @@ namespace mongo {
         private:
             OperationContext* _txn;
             NamespaceString _nss;
-            Lock::DBLock _dblk;
+            AutoGetOrCreateDb _autodb;
             Lock::CollectionLock _collk;
             Context _c;
         };
-
     }; // class Client
 
-
-    /**
-     * RAII-style class, which acquires a lock on the specified database in the requested mode and
-     * obtains a reference to the database. Used as a shortcut for calls to dbHolder().get().
-     *
-     * It is guaranteed that locks will be released when this object goes out of scope, therefore
-     * the database reference returned by this class should not be retained.
-     *
-     * TODO: This should be moved outside of client.h (maybe dbhelpers.h)
-     */
-    class AutoGetDb {
-        MONGO_DISALLOW_COPYING(AutoGetDb);
-    public:
-        AutoGetDb(OperationContext* txn, const StringData& ns, LockMode mode);
-
-        Database* getDb() const {
-            return _db;
-        }
-
-    private:
-        const Lock::DBLock _dbLock;
-        Database* const _db;
-    };
-
-    /**
-     * RAII-style class, which would acquire the appropritate hierarchy of locks for obtaining
-     * a particular collection and would retrieve a reference to the collection.
-     *
-     * It is guaranteed that locks will be released when this object goes out of scope, therefore
-     * database and collection references returned by this class should not be retained.
-     *
-     * TODO: This should be moved outside of client.h (maybe dbhelpers.h)
-     */
-    class AutoGetCollectionForRead {
-        MONGO_DISALLOW_COPYING(AutoGetCollectionForRead);
-    public:
-        AutoGetCollectionForRead(OperationContext* txn, const std::string& ns);
-        AutoGetCollectionForRead(OperationContext* txn, const NamespaceString& nss);
-        ~AutoGetCollectionForRead();
-
-        Database* getDb() const {
-            return _db.getDb();
-        }
-
-        Collection* getCollection() const {
-            return _coll;
-        }
-
-    private:
-        void _init();
-
-        const Timer _timer;
-        OperationContext* const _txn;
-        const NamespaceString _nss;
-        const AutoGetDb _db;
-        const Lock::CollectionLock _collLock;
-
-        Collection* _coll;
-    };
-
-
     /** get the Client object for this thread. */
     inline Client& cc() {
         Client * c = currentClient.get();