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+// Copyright (C) 2013-2020 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 D_PROCESS_H
+#define D_PROCESS_H
+
+#include <asiolink/io_service.h>
+#include <cc/data.h>
+#include <process/d_cfg_mgr.h>
+
+#include <boost/shared_ptr.hpp>
+
+#include <exceptions/exceptions.h>
+
+#include <atomic>
+
+namespace isc {
+namespace process {
+
+/// @brief Exception thrown if the process encountered an operational error.
+class DProcessBaseError : public isc::Exception {
+public:
+    DProcessBaseError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief String value for the version-get command.
+static const std::string VERSION_GET_COMMAND("version-get");
+
+/// @brief String value for the build-report command.
+static const std::string BUILD_REPORT_COMMAND("build-report");
+
+/// @brief String value for the config-get command.
+static const std::string CONFIG_GET_COMMAND("config-get");
+
+/// @brief String value for the config-write command.
+static const std::string CONFIG_WRITE_COMMAND("config-write");
+
+/// @brief String value for the config-test command.
+static const std::string CONFIG_TEST_COMMAND("config-test");
+
+/// @brief String value for the config-reload command.
+static const std::string CONFIG_RELOAD_COMMAND("config-reload");
+
+/// @brief String value for the config-set command.
+static const std::string CONFIG_SET_COMMAND("config-set");
+
+/// @brief String value for the server-tag-get command.
+static const std::string SERVER_TAG_GET_COMMAND("server-tag-get");
+
+/// @brief String value for the shutdown command.
+static const std::string SHUT_DOWN_COMMAND("shutdown");
+
+/// @brief String value for the status-get command.
+static const std::string STATUS_GET_COMMAND("status-get");
+
+/// @brief Returned by the process to indicate a command was successful.
+static const int COMMAND_SUCCESS = 0;
+
+/// @brief Returned by the process to indicates a command failed.
+static const int COMMAND_ERROR = 1;
+
+/// @brief Returned by the process to indicates a command is not valid.
+static const int COMMAND_INVALID = 2;
+
+/// @brief Application Process Interface
+///
+/// DProcessBase is an abstract class represents the primary "application"
+/// level object in a "managed" asynchronous application. It provides a uniform
+/// interface such that a managing layer can construct, initialize, and start
+/// the application's event loop.  The event processing is centered around the
+/// use of isc::asiolink::io_service. The io_service is shared between the
+/// managing layer and the DProcessBase.  This allows management layer IO such
+/// as directives to be sensed and handled, as well as processing IO activity
+/// specific to the application.  In terms of management layer IO, there are
+/// methods shutdown, configuration updates, and commands unique to the
+/// application.
+class DProcessBase {
+public:
+    /// @brief Constructor
+    ///
+    /// @param app_name is a text label for the process. Generally used
+    /// in log statements, but otherwise arbitrary.
+    /// @param io_service is the io_service used by the caller for
+    /// asynchronous event handling.
+    /// @param cfg_mgr the configuration manager instance that handles
+    /// configuration parsing.
+    ///
+    /// @throw DProcessBaseError is io_service is NULL.
+    DProcessBase(const char* app_name, asiolink::IOServicePtr io_service,
+                 DCfgMgrBasePtr cfg_mgr)
+        : app_name_(app_name), io_service_(io_service), shut_down_flag_(false),
+        cfg_mgr_(cfg_mgr) {
+        if (!io_service_) {
+            isc_throw (DProcessBaseError, "IO Service cannot be null");
+        }
+
+        if (!cfg_mgr_) {
+            isc_throw (DProcessBaseError, "CfgMgr cannot be null");
+        }
+    };
+
+    /// @brief May be used after instantiation to perform initialization unique
+    /// to application. It must be invoked prior to invoking run. This would
+    /// likely include the creation of additional IO sources and their
+    /// integration into the io_service.
+    /// @throw DProcessBaseError if the initialization fails.
+    virtual void init() = 0;
+
+    /// @brief Implements the process's event loop. In its simplest form it
+    /// would an invocation io_service_->run().  This method should not exit
+    /// until the process itself is exiting due to a request to shutdown or
+    /// some anomaly is forcing an exit.
+    /// @throw DProcessBaseError if an operational error is encountered.
+    virtual void run() = 0;
+
+    /// @brief Initiates the process's shutdown process.
+    ///
+    /// This is last step in the shutdown event callback chain, that is
+    /// intended to notify the process it is to begin its shutdown process.
+    ///
+    /// @param args an Element set of shutdown arguments (if any) that are
+    /// supported by the process derivation.
+    ///
+    /// @return an Element that contains the results of argument processing,
+    /// consisting of an integer status value (0 means successful,
+    /// non-zero means failure), and a string explanation of the outcome.
+    ///
+    /// @throw DProcessBaseError if an operational error is encountered.
+    virtual isc::data::ConstElementPtr
+    shutdown(isc::data::ConstElementPtr args) = 0;
+
+    /// @brief Processes the given configuration.
+    ///
+    /// This method may be called multiple times during the process lifetime.
+    /// Certainly once during process startup, and possibly later if the user
+    /// alters configuration. This method must not throw, it should catch any
+    /// processing errors and return a success or failure answer as described
+    /// below. On success the last commit timestamp must be updated.
+    ///
+    /// @param config_set a new configuration (JSON) for the process
+    /// @param check_only true if configuration is to be verified only, not applied
+    /// @return an Element that contains the results of configuration composed
+    /// of an integer status value (0 means successful, non-zero means failure),
+    /// and a string explanation of the outcome.
+    virtual isc::data::ConstElementPtr
+    configure(isc::data::ConstElementPtr config_set,
+              bool check_only = false) = 0;
+
+    /// @brief Destructor
+    virtual ~DProcessBase(){};
+
+    /// @brief Checks if the process has been instructed to shut down.
+    ///
+    /// @return true if process shutdown flag is true.
+    bool shouldShutdown() const {
+        return (shut_down_flag_);
+    }
+
+    /// @brief Sets the process shut down flag to the given value.
+    ///
+    /// @param value is the new value to assign the flag.
+    void setShutdownFlag(bool value) {
+        shut_down_flag_ = value;
+    }
+
+    /// @brief Fetches the application name.
+    ///
+    /// @return application name string.
+    const std::string getAppName() const {
+        return (app_name_);
+    }
+
+    /// @brief Fetches the controller's IOService.
+    ///
+    /// @return a reference to the controller's IOService.
+    asiolink::IOServicePtr& getIoService() {
+        return (io_service_);
+    }
+
+    /// @brief Convenience method for stopping IOservice processing.
+    /// Invoking this will cause the process to exit any blocking
+    /// IOService method such as run().  No further IO events will be
+    /// processed.
+    void stopIOService() {
+        io_service_->stop();
+    }
+
+    /// @brief Fetches the process's configuration manager.
+    ///
+    /// @return a reference to the configuration manager.
+    DCfgMgrBasePtr& getCfgMgr() {
+        return (cfg_mgr_);
+    }
+
+private:
+    /// @brief Text label for the process. Generally used in log statements,
+    /// but otherwise can be arbitrary.
+    std::string app_name_;
+
+    /// @brief The IOService to be used for asynchronous event handling.
+    asiolink::IOServicePtr io_service_;
+
+    /// @brief Boolean flag set when shutdown has been requested.
+    std::atomic<bool> shut_down_flag_;
+
+    /// @brief  Pointer to the configuration manager.
+    DCfgMgrBasePtr cfg_mgr_;
+};
+
+/// @brief Defines a shared pointer to DProcessBase.
+typedef boost::shared_ptr<DProcessBase> DProcessBasePtr;
+
+}; // namespace isc::process
+}; // namespace isc
+
+#endif