SERVER-23802 Shut down shard if it rolls back the shardIdentity document.

1 files changed, 85 insertions, 0 deletions

diff --git a/src/mongo/db/s/shard_identity_rollback_notifier.h b/src/mongo/db/s/shard_identity_rollback_notifier.h
new file mode 100644
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+++ b/src/mongo/db/s/shard_identity_rollback_notifier.h
@@ -0,0 +1,85 @@
+/*
+*    Copyright (C) 2016 MongoDB Inc.
+*
+*    This program is free software: you can redistribute it and/or  modify
+*    it under the terms of the GNU Affero General Public License, version 3,
+*    as published by the Free Software Foundation.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU Affero General Public License for more details.
+*
+*    You should have received a copy of the GNU Affero General Public License
+*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*
+*    As a special exception, the copyright holders give permission to link the
+*    code of portions of this program with the OpenSSL library under certain
+*    conditions as described in each individual source file and distribute
+*    linked combinations including the program with the OpenSSL library. You
+*    must comply with the GNU Affero General Public License in all respects for
+*    all of the code used other than as permitted herein. If you modify file(s)
+*    with this exception, you may extend this exception to your version of the
+*    file(s), but you are not obligated to do so. If you do not wish to do so,
+*    delete this exception statement from your version. If you delete this
+*    exception statement from all source files in the program, then also delete
+*    it in the license file.
+*/
+
+#pragma once
+
+#include "mongo/base/disallow_copying.h"
+
+namespace mongo {
+
+class OperationContext;
+class ServiceContext;
+
+/**
+ * Used to detect when a shard's shardIdentity document has been rolled back.  Since rolling back
+ * the shardIdentity document is illegal (as we can't clear the in-memory state associated with it),
+ * we force the mongod to shut down if it happens.  We detect shardIdentity rollback by checking in
+ * the OpObserver for that document to be deleted.  We can't shut down right at that moment,
+ * however, as doing so would interrupt the rollback process and leave the document in place for
+ * when the server is restarted.  Instead, when we detect the shardIdentity document being deleted,
+ * we call recordThatRollbackHappened() on this class, which records the fact that the shardIdentity
+ * document was deleted as part of the rollback, and then when we exit rollback we check
+ * didRollbackHappen() and shut down if so.
+ *
+ * No concurrency control is needed in this class as recordThatRollbackHappened can only happen in
+ * an OpObserver detecting that the document was deleted, and didRollbackHappen is only called on
+ * exiting rollback, and there can only be one of those things happening at any given time.
+ */
+class ShardIdentityRollbackNotifier {
+    MONGO_DISALLOW_COPYING(ShardIdentityRollbackNotifier);
+
+public:
+    ShardIdentityRollbackNotifier();
+
+    /**
+     * Retrieves the ShardIdentityRollbackNotifier associated with the specified service context.
+     */
+    static ShardIdentityRollbackNotifier* get(OperationContext* txn);
+    static ShardIdentityRollbackNotifier* get(ServiceContext* txn);
+
+    /**
+     * Records the fact that the shardIdentity document was rolled back.
+     */
+    void recordThatRollbackHappened() {
+        _rollbackHappened = true;
+    }
+
+    /**
+     * Checks whether the shardIdentity document was rolled back.
+     */
+    bool didRollbackHappen() {
+        return _rollbackHappened;
+    }
+
+private:
+    // Whether or not a rollback of the shardIdentity document has been detected.
+    // No concurrency control necessary since this is only consulted during
+    bool _rollbackHappened = false;
+};
+
+}  // namespace mongo