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, 80 insertions, 0 deletions

diff --git a/src/mongo/db/repl/scatter_gather_algorithm.h b/src/mongo/db/repl/scatter_gather_algorithm.h
new file mode 100644
index 00000000000..7622f0e385e
--- /dev/null
+++ b/src/mongo/db/repl/scatter_gather_algorithm.h
@@ -0,0 +1,80 @@
+/**
+ *    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/db/repl/replication_executor.h"
+
+namespace mongo {
+
+    template <typename T> class StatusWith;
+
+namespace repl {
+
+    /**
+     * Interface for a specialization of a scatter-gather algorithm that sends
+     * requests to a set of targets, and then processes responses until it has
+     * seen enough.
+     *
+     * To use, call getRequests() to get a vector of request objects describing network operations.
+     * Start performing the network operations in any order, and then, until
+     * hasReceivedSufficientResponses() returns true, call processResponse for each response as it
+     * arrives.  Once hasReceivedSufficientResponses() you may cancel outstanding network
+     * operations, and must stop calling processResponse.  Implementations of this interface may
+     * assume that processResponse() is never called after hasReceivedSufficientResponses() returns
+     * true.
+     */
+    class ScatterGatherAlgorithm {
+    public:
+        /**
+         * Returns the list of requests that should be sent.
+         */
+        virtual std::vector<ReplicationExecutor::RemoteCommandRequest> getRequests() const = 0;
+
+        /**
+         * Method to call once for each received response.
+         */
+        virtual void processResponse(
+                const ReplicationExecutor::RemoteCommandRequest& request,
+                const ResponseStatus& response) = 0;
+
+        /**
+         * Returns true if no more calls to processResponse are needed to consider the
+         * algorithm complete.  Once this method returns true, one should no longer
+         * call processResponse.
+         */
+        virtual bool hasReceivedSufficientResponses() const = 0;
+
+    protected:
+        virtual ~ScatterGatherAlgorithm();  // Shouldn't actually be virtual.
+    };
+
+}  // namespace repl
+}  // namespace mongo