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// Copyright (C) 2022 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef TCP_CONNECTION_POOL_H
#define TCP_CONNECTION_POOL_H
#include <tcp/tcp_connection.h>
#include <list>
#include <mutex>
namespace isc {
namespace tcp {
/// @brief Type of TCP connection pointer list.
typedef std::list<TcpConnectionPtr> TcpConnectionList;
/// @brief Pool of active TCP connections.
///
/// The TCP server is designed to handle many connections simultaneously.
/// The communication between the client and the server may take long time
/// and the server must be able to react on other events while the communication
/// with the clients is in progress. Thus, the server must track active
/// connections and gracefully close them when needed. An obvious case when the
/// connections must be terminated by the server is when the shutdown signal
/// is received.
///
/// This object is a simple container for the server connections which provides
/// means to terminate them on request.
class TcpConnectionPool {
public:
/// @brief Start new connection.
///
/// The connection is inserted to the pool and the
/// @ref TcpConnection::asyncAccept is invoked.
///
/// @param connection Pointer to the new connection.
void start(const TcpConnectionPtr& connection);
/// @brief Removes a connection from the pool and shutdown it.
///
/// Shutdown is specific to TLS and is a first part of graceful close
/// (note it is NOT the same as TCP shutdown system call).
///
/// @note if the TLS connection stalls e.g. the peer does not try I/O
/// on it the connection has to be explicitly stopped.
///
/// @param connection Pointer to the connection.
void shutdown(const TcpConnectionPtr& connection);
/// @brief Removes a connection from the pool and stops it.
///
/// @param connection Pointer to the connection.
void stop(const TcpConnectionPtr& connection);
/// @brief Stops all connections and removes them from the pool.
///
/// @note This function is not thread-safe so should be called
/// when the thread pool is stopped.
void stopAll();
/// @brief Returns the number of connections using a given remote IP address.
///
/// Used to limit the number of connections when accepting a new one.
///
/// @param remote_ip The remote IP address.
/// @param[out] total_connections Size of the connection pool.
/// @return The number of connections using a given remote IP address.
size_t usedByRemoteIp(const asiolink::IOAddress& remote_ip,
size_t& total_connections);
/// @brief Class/static started (i.e. added to pool) connection counter.
static std::atomic<uint64_t> started_counter_;
/// @brief Class/static stopped (i.e. removed from pool) connection counter.
static std::atomic<uint64_t> stopped_counter_;
/// @brief Class/static rejected (by the accept filter) connection counter.
static std::atomic<uint64_t> rejected_counter_;
protected:
/// @brief Stops all connections and removes them from the pool.
///
/// Must be called from with a thread-safe context.
void stopAllInternal();
/// @brief Returns the number of connections using a given remote IP address.
///
/// Used to limit the number of connections when accepting a new one.
/// Must be called from with a thread-safe context.
///
/// @param remote_ip The remote IP address.
/// @param[out] total_connections Size of the connection pool.
/// @return The number of connections using a given remote IP address.
size_t usedByRemoteIpInternal(const asiolink::IOAddress& remote_ip,
size_t& total_connections);
/// @brief Set of connections.
TcpConnectionList connections_;
/// @brief Mutex to protect the internal state.
std::mutex mutex_;
};
}
}
#endif
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