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+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    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 Server Side 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/client/sdam/sdam_datatypes.h"
+#include "mongo/client/sdam/topology_listener.h"
+#include "mongo/executor/task_executor.h"
+#include "mongo/util/net/hostandport.h"
+
+namespace mongo {
+
+/**
+ * Manages server monitoring for a single server. Broadcasts the RTT (Round Trip Time) to a
+ * listener.
+ */
+class SingleServerPingMonitor : public std::enable_shared_from_this<SingleServerPingMonitor> {
+public:
+    explicit SingleServerPingMonitor(sdam::ServerAddress hostAndPort,
+                                     sdam::TopologyListener* rttListener,
+                                     Seconds pingFrequency,
+                                     std::shared_ptr<executor::TaskExecutor> executor);
+
+    /**
+     * Signals that the SingleServerPingMonitor has been dropped and should cancel any outstanding
+     * pings scheduled to execute in the future. Contract: Once drop() is completed, the
+     * SingleServerPingMonitor will stop broadcasting results to the listener.
+     */
+    void drop();
+
+private:
+    sdam::ServerAddress _hostAndPort;
+
+    /**
+     * Listens for when new RTT (Round Trip Time) values are published.
+     */
+    sdam::TopologyListener* _rttListener;
+
+    /**
+     * The frequency at which ping requests should be sent to measure the round trip time.
+     */
+    Seconds _pingFrequency;
+
+
+    std::shared_ptr<executor::TaskExecutor> _executor;
+};
+
+
+/**
+ * Monitors the RTT (Round Trip Time) for a set of servers.
+ */
+class ServerPingMonitor {
+    ServerPingMonitor(const ServerPingMonitor&) = delete;
+    ServerPingMonitor& operator=(const ServerPingMonitor&) = delete;
+
+public:
+    /**
+     * Note: The ServerPingMonitor creates its own executor by default. It takes in an executor for
+     * testing only.
+     */
+    ServerPingMonitor(
+        sdam::TopologyListener* rttListener,
+        Seconds pingFrequency,
+        boost::optional<std::shared_ptr<executor::TaskExecutor>> executor = boost::none);
+    ~ServerPingMonitor();
+
+    /**
+     * The first isMaster exchange for a server succeeded. Creates a new
+     * SingleServerPingMonitor to monitor the new replica set member.
+     */
+    void onServerHandshakeCompleteEvent(sdam::ServerAddress address, OID topologyId);
+
+    /**
+     * The connection to the server was closed. Removes the server from the ServerPingMonitorList.
+     */
+    void onServerClosedEvent(sdam::ServerAddress address, OID topologyId);
+
+private:
+    /**
+     * Sets up and starts up the _executor. Creates a new executor if one wasn't provided.
+     */
+    void _setupTaskExecutor(boost::optional<std::shared_ptr<executor::TaskExecutor>> executor);
+
+    /**
+     * Listens for when new RTT (Round Trip Time) values are published.
+     */
+    sdam::TopologyListener* _rttListener;
+
+    /**
+     * Executor for performing server monitoring pings for all of the replica set members.
+     */
+    std::shared_ptr<executor::TaskExecutor> _executor;
+
+    /**
+     * The interval at which ping requests should be sent to measure the RTT (Round Trip Time).
+     */
+    Seconds _pingFrequency;
+
+    mutable Mutex _mutex = MONGO_MAKE_LATCH("ServerPingMonitor::mutex");
+
+    /**
+     * Maps each server to a SingleServerPingMonitor.
+     * Note: SingleServerPingMonitor's drop() should always be called before removing it from the
+     * _serverPingMonitorMap.
+     */
+    stdx::unordered_map<sdam::ServerAddress, std::unique_ptr<SingleServerPingMonitor>>
+        _serverPingMonitorMap;
+};
+
+}  // namespace mongo