SERVER-18901 Move Fetcher and QueryFetcher to mongo/client/

1 files changed, 186 insertions, 0 deletions

diff --git a/src/mongo/client/fetcher.h b/src/mongo/client/fetcher.h
new file mode 100644
index 00000000000..32b1c5aa8cb
--- /dev/null
+++ b/src/mongo/client/fetcher.h
@@ -0,0 +1,186 @@
+/**
+ *    Copyright (C) 2015 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 <string>
+#include <vector>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/status.h"
+#include "mongo/base/status_with.h"
+#include "mongo/bson/bsonobj.h"
+#include "mongo/db/clientcursor.h"
+#include "mongo/db/namespace_string.h"
+#include "mongo/executor/task_executor.h"
+#include "mongo/stdx/functional.h"
+#include "mongo/stdx/condition_variable.h"
+#include "mongo/stdx/mutex.h"
+#include "mongo/util/net/hostandport.h"
+
+namespace mongo {
+    class Fetcher {
+        MONGO_DISALLOW_COPYING(Fetcher);
+    public:
+
+        /**
+         * Container for BSON documents extracted from cursor results.
+         */
+        typedef std::vector<BSONObj> Documents;
+
+        /**
+         * Documents in current batch with cursor ID and associated namespace name.
+         * If cursor ID is zero, there are no additional batches.
+         */
+        struct BatchData {
+            BatchData() = default;
+            BatchData(CursorId theCursorId, const NamespaceString& theNss, Documents theDocuments);
+            CursorId cursorId = 0;
+            NamespaceString nss;
+            Documents documents;
+        };
+
+        /**
+         * Represents next steps of fetcher.
+         */
+        enum class NextAction : int {
+            kInvalid=0,
+            kNoAction=1,
+            kGetMore=2
+        };
+
+        /**
+         * Type of a fetcher callback function.
+         */
+        typedef stdx::function<void (const StatusWith<BatchData>&,
+                                     NextAction*,
+                                     BSONObjBuilder*)> CallbackFn;
+
+        /**
+         * Creates Fetcher task but does not schedule it to be run by the executor.
+         *
+         * First remote command to be run by the executor will be 'cmdObj'. The results
+         * of 'cmdObj' must contain a cursor response object.
+         * See Commands::appendCursorResponseObject.
+         *
+         * Callback function 'work' will be called 1 or more times after a successful
+         * schedule() call depending on the results of the remote command.
+         *
+         * Depending on the cursor ID in the initial cursor response object, the fetcher may run
+         * subsequent getMore commands on the remote server in order to obtain a complete
+         * set of results.
+         *
+         * Failed remote commands will also cause 'work' to be invoked with the
+         * error details provided by the remote server. On failure, the fetcher will stop
+         * sending getMore requests to the remote server.
+         *
+         * If the fetcher is canceled (either by calling cancel() or shutting down the executor),
+         * 'work' will not be invoked.
+         *
+         * Fetcher uses the NextAction argument to inform client via callback if a getMore command
+         * will be scheduled to be run by the executor to retrieve additional results.
+         * Also, note that the NextAction is both an input and output argument to allow
+         * the client to suggest a different action for the fetcher to take post-callback.
+         *
+         * The callback function 'work' is not allowed to call into the Fetcher instance. This
+         * behavior is undefined and may result in a deadlock.
+         */
+        Fetcher(executor::TaskExecutor* executor,
+                const HostAndPort& source,
+                const std::string& dbname,
+                const BSONObj& cmdObj,
+                const CallbackFn& work);
+
+        virtual ~Fetcher();
+
+        /**
+         * Returns diagnostic information.
+         */
+        std::string getDiagnosticString() const;
+
+        /**
+         * Returns true if a remote command has been scheduled (but not completed)
+         * with the executor.
+         */
+        bool isActive() const;
+
+        /**
+         * Schedules 'cmdObj' to be run on the remote server.
+         */
+        Status schedule();
+
+        /**
+         * Cancels remote command request.
+         * Returns immediately if fetcher is not active.
+         */
+        void cancel();
+
+        /**
+         * Waits for remote command requests to complete.
+         * Returns immediately if fetcher is not active.
+         */
+        void wait();
+
+    private:
+
+        /**
+         * Schedules remote command to be run by the executor
+         */
+        Status _schedule_inlock(const BSONObj& cmdObj, const char* batchFieldName);
+
+        /**
+         * Callback for remote command.
+         */
+        void _callback(const executor::TaskExecutor::RemoteCommandCallbackArgs& rcbd,
+                       const char* batchFieldName);
+
+        /**
+         * Sets fetcher state to inactive and notifies waiters.
+         */
+        void _finishCallback();
+
+        // Not owned by us.
+        executor::TaskExecutor* _executor;
+
+        HostAndPort _source;
+        std::string _dbname;
+        BSONObj _cmdObj;
+        CallbackFn _work;
+
+        // Protects member data of this Fetcher.
+        mutable stdx::mutex _mutex;
+
+        mutable stdx::condition_variable _condition;
+
+        // _active is true when Fetcher is scheduled to be run by the executor.
+        bool _active;
+        // Callback handle to the scheduled remote command.
+        executor::TaskExecutor::CallbackHandle _remoteCommandCallbackHandle;
+    };
+
+} // namespace mongo