SERVER-15248 Introduce ScatterGatherAlgorithm interface and ScatterGatherRunner.

The ScatterGatherAlgorithm interface describes operations that a scatter-gather
process must perform.  ScatterGatherRunner uses a ReplicationExecutor to
execute a ScatterGatherAlgorithm.

1 files changed, 115 insertions, 0 deletions

diff --git a/src/mongo/db/repl/scatter_gather_runner.h b/src/mongo/db/repl/scatter_gather_runner.h
new file mode 100644
index 00000000000..835405ed31f
--- /dev/null
+++ b/src/mongo/db/repl/scatter_gather_runner.h
@@ -0,0 +1,115 @@
+/**
+ *    Copyright 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 <vector>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/db/repl/replication_executor.h"
+#include "mongo/stdx/functional.h"
+
+namespace mongo {
+
+    template <typename T> class StatusWith;
+
+namespace repl {
+
+    class ScatterGatherAlgorithm;
+
+    /**
+     * Implementation of a scatter-gather behavior using a ReplicationExecutor.
+     */
+    class ScatterGatherRunner {
+        MONGO_DISALLOW_COPYING(ScatterGatherRunner);
+    public:
+        /**
+         * Constructs a new runner whose underlying algorithm is "algorithm".
+         *
+         * "algorithm" must remain in scope until the runner's destructor completes.
+         */
+        explicit ScatterGatherRunner(ScatterGatherAlgorithm* algorithm);
+
+        ~ScatterGatherRunner();
+
+        /**
+         * Runs the scatter-gather process using "executor", and blocks until it completes.
+         *
+         * Must _not_ be run from inside the executor context.
+         *
+         * Returns ErrorCodes::ShutdownInProgress if the executor enters or is already in
+         * the shutdown state before run() can schedule execution of the scatter-gather
+         * in the executor.  Note that if the executor is shut down after the algorithm
+         * is scheduled but before it completes, this method will return Status::OK(),
+         * just as it does when it runs successfully to completion.
+         */
+        Status run(ReplicationExecutor* executor);
+
+        /**
+         * Starts executing the scatter-gather process using "executor".
+         *
+         * On success, returns an event handle that will be signaled when the runner has
+         * finished executing the scatter-gather process.  After that event has been
+         * signaled, it is safe for the caller to examine any state on "algorithm".
+         *
+         * This method must be called inside the executor context.
+         *
+         * onCompletion is an optional callback that will be executed in executor context
+         * immediately prior to signaling the event handle returned here. It must never
+         * throw exceptions.  It may examine the state of the algorithm object.
+         *
+         * NOTE: If the executor starts to shut down before onCompletion executes, onCompletion may
+         * never execute, even though the returned event will eventually be signaled.
+         */
+        StatusWith<ReplicationExecutor::EventHandle> start(
+                ReplicationExecutor* executor,
+                const stdx::function<void ()>& onCompletion = stdx::function<void ()>());
+
+    private:
+        /**
+         * Callback invoked once for every response from the network.
+         */
+        static void _processResponse(const ReplicationExecutor::RemoteCommandCallbackData& cbData,
+                                     ScatterGatherRunner* runner);
+
+        /**
+         * Method that performs all actions required when _algorithm indicates a sufficient
+         * number of respones have been received.
+         */
+        void _signalSufficientResponsesReceived(ReplicationExecutor* executor);
+
+        ScatterGatherAlgorithm* _algorithm;
+        stdx::function<void ()> _onCompletion;
+        ReplicationExecutor::EventHandle _sufficientResponsesReceived;
+        std::vector<ReplicationExecutor::CallbackHandle> _callbacks;
+        size_t _actualResponses;
+        bool _started;
+    };
+
+}  // namespace repl
+}  // namespace mongo