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+/**
+ *    Copyright (C) 2014 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 <memory>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/status.h"
+#include "mongo/db/ops/update_driver.h"
+#include "mongo/db/ops/update_result.h"
+
+namespace mongo {
+
+    class CanonicalQuery;
+    class OpDebug;
+    class UpdateRequest;
+
+    /**
+     * Implementation of the processing of an update operation in a mongod.
+     *
+     * The executor has two important methods, prepare() and execute().  The prepare() method can
+     * run without locks, and does whatever parsing and precomputation can be done without access to
+     * database data.  The execute method performs the update, but the caller must already hold the
+     * appropriate database lock.
+     *
+     * Expected usage is approximately:
+     *   UpdateRequest request(...);
+     *   // configure request
+     *   UpdateExecutor executor(&request, opDebug);
+     *   uassertStatusOK(executor.prepare());
+     *   // Get locks, get ready to execute.
+     *   try {
+     *       UpdateResult res = executor.execute();
+     *   }
+     *   catch (const DBException& ex) {
+     *       // Error handling.
+     *   }
+     */
+    class UpdateExecutor {
+        MONGO_DISALLOW_COPYING(UpdateExecutor);
+    public:
+        /**
+         * Constructs an update executor.
+         *
+         * The objects pointed to by "request" and "opDebug" must stay in scope for the life of the
+         * constructed executor.
+         */
+        UpdateExecutor(const UpdateRequest* request, OpDebug* opDebug);
+
+        ~UpdateExecutor();
+
+        /**
+         * Performs preparatory work that does not require database locks.
+         *
+         * Returns Status::OK() on success.  Other results indicate that the executor will not run
+         * correctly, and should be abandoned.
+         *
+         * Calling prepare() is optional.  It is available for situations in which the user
+         * wishes to do as much work as possible before acquiring database locks.
+         */
+        Status prepare();
+
+        /**
+         * Execute an update.  Requires the caller to hold the database lock on the
+         * appropriate resources for the request.
+         */
+        UpdateResult execute();
+
+    private:
+        /**
+         * Parses the query portion of the update request.
+         */
+        Status parseQuery();
+
+        /**
+         * Parses the update-descriptor portion of the update request.
+         */
+        Status parseUpdate();
+
+        /// Unowned pointer to the request object that this executor will process.
+        const UpdateRequest* const _request;
+
+        /// Unowned pointer to the opdebug object that this executor will populate with debug data.
+        OpDebug* const _opDebug;
+
+        /// Driver for processing updates on matched documents.
+        UpdateDriver _driver;
+
+        /// Parsed query object, or NULL if the query proves to be an id hack query.
+        std::auto_ptr<CanonicalQuery> _canonicalQuery;
+
+        /// Flag indicating if the query has been successfully parsed.
+        bool _isQueryParsed;
+
+        /// Flag indicatin gif the update description has been successfully parsed.
+        bool _isUpdateParsed;
+    };
+
+}  // namespace mongo