LinuxStarter.h

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/*
 * This file is part of ArmarX.
 *
 * Copyright (C) 2011-2016, High Performance Humanoid Technologies (H2T), Karlsruhe Institute of Technology (KIT), all rights reserved.
 *
 * ArmarX is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * ArmarX 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 *
 * @package    ArmarXCore::core
 * @author     Nicola Miskowiec
 * @date       2016
 * @copyright  http://www.gnu.org/licenses/gpl-2.0.txt
 *             GNU General Public License
 */
 
 
#pragma once
 
#include <optional>
#include <string>
#include <vector>
 
#include "../data_structure/ApplicationInstance.h"
#include "../parser/StatusManager.h"
#include "ApplicationStarter.h"
 
namespace ScenarioManager::Exec
{
    /**
    * @class LinuxStarter
    * @ingroup exec
    * @brief Starts applications in Linux. Shouldn't be used in any other OS, due to system calls being used.
    * Applications started this way will still run, even when the main application dies.
    * Can also be used to request the status of an application.
    */
    class LinuxStarter : public ApplicationStarter
    {
    public:
        LinuxStarter();
 
        /**
        * Starts an application. Forks, creates a daemon and starts the executable.
        * @param application application to be started
        */
        virtual void startApplication(Data_Structure::ApplicationInstancePtr application,
                                      StatusManager statusManager,
                                      const std::string& commandLineParameters = "",
                                      bool printOnly = false) override;
 
        /**
        * Returns the status of an application.
        * @param application application whose status is returned
        * @return status of the application
        */
        virtual std::string getStatus(Data_Structure::ApplicationInstancePtr application,
                                      StatusManager statusManager) override;
 
    private:
        /**
         * What a probe of a single pid could establish.
         *
         * The distinction between Dead and Indeterminate matters: only a *confirmed* death may
         * make us forget the pid of an application. Treating "could not read /proc" as a death -
         * which is what the status probe used to do - permanently loses a running application,
         * because nothing ever looked for it again.
         */
        enum class ProcessState
        {
            /// The process exists and is scheduled or sleeping.
            Alive,
            /// The process provably no longer exists.
            Dead,
            /// The process exists but its state could not be established, or it could not be read
            /// at all while still being present in /proc.
            Indeterminate
        };
 
        /**
         * Sets SIGCHLD to SIG_IGN for the whole process, so that the applications we launch and
         * never wait for do not pile up as zombies.
         *
         * Called before every launch rather than once, because the disposition can be taken over
         * by anything else in the process - Qt's QProcess does so on first use - which switches
         * the kernel's auto-reaping off again without our noticing.
         */
        static void EnsureChildrenAreReaped();
 
        /**
         * @brief probeProcessState reads the scheduler state of the process with the given pid.
         *
         * Takes the pid instead of the application so that it cannot observe a pid that is
         * concurrently changed by a starter or stopper thread halfway through.
         */
        static ProcessState probeProcessState(int pid);
 
        /**
         * @brief findRunningProcess looks for a live process belonging to `application` among all
         * processes whose executable name matches, and returns its pid, or -1 if there is none.
         *
         * This is what lets the ScenarioManager recover an application whose pid it lost, and what
         * lets it see an application that was started outside of it. Candidates are attributed via
         * the `--Ice.Config=` argument the ScenarioManager passes on launch; a candidate that
         * carries a config belonging to a *different* application instance is rejected outright,
         * and an ambiguous set of candidates is never guessed at.
         *
         * @param ambiguous set to true when processes matched but could not be attributed to
         * exactly one application - the caller should report Unknown rather than Stopped.
         */
        static int findRunningProcess(const Data_Structure::ApplicationInstancePtr& application,
                                      bool& ambiguous);
 
        /**
         * @brief adoptRunningProcess looks for a live process belonging to `application` via
         * findRunningProcess() and, if it finds one, takes ownership of its pid.
         *
         * Called on every path that would otherwise report "Stopped", so that neither a lost pid
         * nor a launch outside the ScenarioManager leaves a running application shown as stopped.
         *
         * @return the status to report for the application.
         */
        static std::string
        adoptRunningProcess(const Data_Structure::ApplicationInstancePtr& application,
                            StatusManager& statusManager);
 
        /**
         * @brief rediscover looks for a live process belonging to `application` and hands the
         * application over to it, replacing the pid it currently holds.
         *
         * Used when the pid we hold can no longer be confirmed to be this application - it has
         * been recycled by an unrelated process, or it can no longer be read at all - but the
         * application itself may well be running elsewhere. Unlike adoptRunningProcess() this does
         * not require the application's pid to be unset.
         *
         * @param stalePid the pid the application is expected to hold; the handover is abandoned
         * if it has changed in the meantime, so that a concurrent start always wins.
         * @return the status to report, or nothing if no better process was found and the caller
         * should stick with its own conclusion.
         */
        static std::optional<std::string>
        rediscover(const Data_Structure::ApplicationInstancePtr& application,
                   StatusManager& statusManager,
                   int stalePid);
    };
 
} // namespace ScenarioManager::Exec