[oweals/dinit.git] / src / service.h

#ifndef SERVICE_H
#define SERVICE_H

#include <string>
#include <list>
#include <vector>
#include <csignal>
#include <unordered_set>

#include "dasynq.h"

#include "control.h"
#include "service-listener.h"
#include "service-constants.h"

/*
 * This header defines ServiceRecord, a data record maintaining information about a service,
 * and ServiceSet, a set of interdependent service records. It also defines some associated
 * types and exceptions.
 *
 * Service states
 * --------------
 * Services have both a current state and a desired state. The desired state can be
 * either STARTED or STOPPED. The current state can also be STARTING or STOPPING.
 * A service can be "pinned" in either the STARTED or STOPPED states to prevent it
 * from leaving that state until it is unpinned.
 *
 * The total state is a combination of the two, current and desired:
 *      STOPPED/STOPPED  : stopped and will remain stopped
 *      STOPPED/STARTED  : stopped (pinned), must be unpinned to start
 *      STARTING/STARTED : starting, but not yet started. Dependencies may also be starting.
 *      STARTING/STOPPED : as above, but the service will be stopped again as soon as it has
 *                         completed startup.
 *      STARTED/STARTED  : running and will continue running.
 *      STARTED/STOPPED  : started (pinned), must be unpinned to stop
 *      STOPPING/STOPPED : stopping and will stop. Dependents may be stopping.
 *      STOPPING/STARTED : as above, but the service will be re-started again once it stops.
 *
 * A scripted service is in the STARTING/STOPPING states during the script execution.
 * A process service is in the STOPPING state when it has been signalled to stop, and is
 * in the STARTING state when waiting for dependencies to start or for the exec() call in
 * the forked child to complete and return a status.
 *
 * Acquisition/release:
 * ------------------
 * Each service has a dependent-count ("required_by"). This starts at 0, adds 1 if the
 * service has explicitly been started (i.e. "start_explicit" is true), and adds 1 for
 * each dependent service which is not STOPPED (including dependents with a soft dependency).
 * When required_by transitions to 0, the service is stopped (unless it is pinned). When
 * require_by transitions from 0, the service is started (unless pinned).
 *
 * So, in general, the dependent-count determines the desired state (STARTED if the count
 * is greater than 0, otherwise STOPPED). However, a service can be issued a stop-and-take
 * down order (via `stop(true)'); this will first stop dependent services, which may restart
 * and cancel the stop of the former service. Finally, a service can be force-stopped, which
 * means that its stop process cannot be cancelled (though it may still be put in a desired
 * state of STARTED, meaning it will start immediately upon stopping).
 *
 * Pinning
 * -------
 * A service may be "pinned" in either STARTED or STOPPED states (or even both). Once it
 * reaches a pinned state, a service will not leave that state, though its desired state
 * may still be set. (Note that pinning prevents, but never causes, state transition).
 *
 * The priority of the different state deciders is:
 *  - pins
 *  - force stop flag
 *  - desired state (which is manipulated by require/release operations)
 *
 * So a forced stop cannot occur until the service is not pinned started, for instance.
 *
 * Two-phase transition
 * --------------------
 * Transition between states occurs in two phases: propagation and execution. In the
 * propagation phase, acquisition/release messages are processed, and desired state may be
 * altered accordingly. Desired state of dependencies/dependents should not be examined in
 * this phase, since it may change during the phase (i.e. its current value at any point
 * may not reflect the true final value).
 *
 * In the execution phase, actions are taken to achieve the desired state. Actual state may
 * transition according to the current and desired states.
 */

struct OnstartFlags {
    bool rw_ready : 1;
    bool log_ready : 1;
    
    // Not actually "onstart" commands:
    bool no_sigterm : 1;  // do not send SIGTERM
    bool runs_on_console : 1;  // run "in the foreground"
    bool pass_cs_fd : 1;  // pass this service a control socket connection via fd
    
    OnstartFlags() noexcept : rw_ready(false), log_ready(false),
            no_sigterm(false), runs_on_console(false), pass_cs_fd(false)
    {
    }
};

// Exception while loading a service
class ServiceLoadExc
{
    public:
    std::string serviceName;
    const char *excDescription;
    
    protected:
    ServiceLoadExc(std::string serviceName, const char *desc) noexcept
        : serviceName(serviceName), excDescription(desc)
    {
    }
};

class ServiceNotFound : public ServiceLoadExc
{
    public:
    ServiceNotFound(std::string serviceName) noexcept
        : ServiceLoadExc(serviceName, "Service description not found.")
    {
    }
};

class ServiceCyclicDependency : public ServiceLoadExc
{
    public:
    ServiceCyclicDependency(std::string serviceName) noexcept
        : ServiceLoadExc(serviceName, "Has cyclic dependency.")
    {
    }
};

class ServiceDescriptionExc : public ServiceLoadExc
{
    public:
    ServiceDescriptionExc(std::string serviceName, std::string extraInfo) noexcept
        : ServiceLoadExc(serviceName, extraInfo.c_str())
    {
    }    
};

class ServiceRecord;
class ServiceSet;
class base_process_service;

/* Service dependency record */
class ServiceDep
{
    ServiceRecord * from;
    ServiceRecord * to;

    public:
    /* Whether the 'from' service is waiting for the 'to' service to start */
    bool waiting_on;
    /* Whether the 'from' service is holding an acquire on the 'to' service */
    bool holding_acq;

    ServiceDep(ServiceRecord * from, ServiceRecord * to) noexcept : from(from), to(to), waiting_on(false), holding_acq(false)
    {  }

    ServiceRecord * getFrom() noexcept
    {
        return from;
    }

    ServiceRecord * getTo() noexcept
    {
        return to;
    }
};

// Given a string and a list of pairs of (start,end) indices for each argument in that string,
// store a null terminator for the argument. Return a `char *` vector containing the beginning
// of each argument and a trailing nullptr. (The returned array is invalidated if the string is later modified).
static std::vector<const char *> separate_args(std::string &s, std::list<std::pair<unsigned,unsigned>> &arg_indices)
{
    std::vector<const char *> r;
    r.reserve(arg_indices.size() + 1);

    // First store nul terminator for each part:
    for (auto index_pair : arg_indices) {
        if (index_pair.second < s.length()) {
            s[index_pair.second] = 0;
        }
    }

    // Now we can get the C string (c_str) and store offsets into it:
    const char * cstr = s.c_str();
    for (auto index_pair : arg_indices) {
        r.push_back(cstr + index_pair.first);
    }
    r.push_back(nullptr);
    return r;
}

class ServiceChildWatcher : public EventLoop_t::child_proc_watcher_impl<ServiceChildWatcher>
{
    public:
    base_process_service * service;
    rearm child_status(EventLoop_t &eloop, pid_t child, int status) noexcept;
    
    ServiceChildWatcher(base_process_service * sr) noexcept : service(sr) { }
};

class ServiceIoWatcher : public EventLoop_t::fd_watcher_impl<ServiceIoWatcher>
{
    public:
    base_process_service * service;
    rearm fd_event(EventLoop_t &eloop, int fd, int flags) noexcept;
    
    ServiceIoWatcher(base_process_service * sr) noexcept : service(sr) { }
};

class ServiceRecord
{
    protected:
    typedef std::string string;
    
    string service_name;
    ServiceType service_type;  /* ServiceType::DUMMY, PROCESS, SCRIPTED, INTERNAL */
    ServiceState service_state = ServiceState::STOPPED; /* ServiceState::STOPPED, STARTING, STARTED, STOPPING */
    ServiceState desired_state = ServiceState::STOPPED; /* ServiceState::STOPPED / STARTED */

    string program_name;          // storage for program/script and arguments
    std::vector<const char *> exec_arg_parts; // pointer to each argument/part of the program_name, and nullptr
    
    string stop_command;          // storage for stop program/script and arguments
    std::vector<const char *> stop_arg_parts; // pointer to each argument/part of the stop_command, and nullptr
    
    string pid_file;
    
    OnstartFlags onstart_flags;

    string logfile;           // log file name, empty string specifies /dev/null
    
    bool auto_restart : 1;    // whether to restart this (process) if it dies unexpectedly
    bool smooth_recovery : 1; // whether the service process can restart without bringing down service
    
    bool pinned_stopped : 1;
    bool pinned_started : 1;
    bool waiting_for_deps : 1;  // if STARTING, whether we are waiting for dependencies (inc console) to start
    bool waiting_for_execstat : 1;  // if we are waiting for exec status after fork()
    bool start_explicit : 1;    // whether we are are explictly required to be started

    bool prop_require : 1;      // require must be propagated
    bool prop_release : 1;      // release must be propagated
    bool prop_failure : 1;      // failure to start must be propagated
    
    int required_by = 0;        // number of dependents wanting this service to be started

    typedef std::list<ServiceRecord *> sr_list;
    typedef sr_list::iterator sr_iter;
    
    // list of soft dependencies
    typedef std::list<ServiceDep> softdep_list;
    
    // list of soft dependents
    typedef std::list<ServiceDep *> softdpt_list;
    
    sr_list depends_on; // services this one depends on
    sr_list dependents; // services depending on this one
    softdep_list soft_deps;  // services this one depends on via a soft dependency
    softdpt_list soft_dpts;  // services depending on this one via a soft dependency
    
    // unsigned wait_count;  /* if we are waiting for dependents/dependencies to
    //                         start/stop, this is how many we're waiting for */
    
    ServiceSet *service_set; // the set this service belongs to
    
    std::unordered_set<ServiceListener *> listeners;
    
    // Process services:
    bool force_stop; // true if the service must actually stop. This is the
                     // case if for example the process dies; the service,
                     // and all its dependencies, MUST be stopped.
    
    int term_signal = -1;  // signal to use for process termination
    
    string socket_path; // path to the socket for socket-activation service
    int socket_perms;   // socket permissions ("mode")
    uid_t socket_uid = -1;  // socket user id or -1
    gid_t socket_gid = -1;  // socket group id or -1

    // Implementation details
    
    pid_t pid = -1;  // PID of the process. If state is STARTING or STOPPING,
                     //   this is PID of the service script; otherwise it is the
                     //   PID of the process itself (process service).
    int exit_status; // Exit status, if the process has exited (pid == -1).
    int socket_fd = -1;  // For socket-activation services, this is the file
                         // descriptor for the socket.
    
    
    // Data for use by ServiceSet
    public:
    
    // Next service (after this one) in the queue for the console. Intended to only be used by ServiceSet class.
    ServiceRecord *next_for_console;
    
    // Propagation and start/stop queues
    ServiceRecord *next_in_prop_queue = nullptr;
    ServiceRecord *next_in_stop_queue = nullptr;
    
    
    protected:
    
    // All dependents have stopped.
    virtual void all_deps_stopped() noexcept;
    
    // Service has actually stopped (includes having all dependents
    // reaching STOPPED state).
    void stopped() noexcept;
    
    // Service has successfully started
    void started() noexcept;
    
    // Service failed to start (only called when in STARTING state).
    //   dep_failed: whether failure is recorded due to a dependency failing
    void failed_to_start(bool dep_failed = false) noexcept;

    void run_child_proc(const char * const *args, const char *logfile, bool on_console, int wpipefd,
            int csfd) noexcept;
    
    // Callback from libev when a child process dies
    static void process_child_callback(EventLoop_t *loop, ServiceChildWatcher *w,
            int revents) noexcept;
    
    //virtual void handle_exit_status(int exit_status) noexcept;

    // A dependency has reached STARTED state
    void dependencyStarted() noexcept;
    
    void allDepsStarted(bool haveConsole = false) noexcept;

    // Do any post-dependency startup; return false on failure
    virtual bool start_ps_process() noexcept;

    // Open the activation socket, return false on failure
    bool open_socket() noexcept;

    // Check whether dependencies have started, and optionally ask them to start
    bool startCheckDependencies(bool do_start) noexcept;

    // Whether a STARTING service can immediately transition to STOPPED (as opposed to
    // having to wait for it reach STARTED and then go through STOPPING).
    bool can_interrupt_start() noexcept
    {
        return waiting_for_deps;
    }
    
    // Whether a STOPPING service can immediately transition to STARTED.
    bool can_interrupt_stop() noexcept
    {
        return waiting_for_deps && ! force_stop;
    }

    // A dependent has reached STOPPED state
    void dependentStopped() noexcept;

    // check if all dependents have stopped
    bool stopCheckDependents() noexcept;
    
    // issue a stop to all dependents, return true if they are all already stopped
    bool stopDependents() noexcept;
    
    void require() noexcept;
    void release() noexcept;
    void release_dependencies() noexcept;
    
    // Check if service is, fundamentally, stopped.
    bool is_stopped() noexcept
    {
        return service_state == ServiceState::STOPPED
            || (service_state == ServiceState::STARTING && waiting_for_deps);
    }
    
    void notifyListeners(ServiceEvent event) noexcept
    {
        for (auto l : listeners) {
            l->serviceEvent(this, event);
        }
    }
    
    // Queue to run on the console. 'acquiredConsole()' will be called when the console is available.
    void queueForConsole() noexcept;
    
    // Release console (console must be currently held by this service)
    void releaseConsole() noexcept;
    
    bool do_auto_restart() noexcept;

    // Started state reached
    bool process_started() noexcept;

    public:

    ServiceRecord(ServiceSet *set, string name)
        : service_state(ServiceState::STOPPED), desired_state(ServiceState::STOPPED), auto_restart(false),
            pinned_stopped(false), pinned_started(false), waiting_for_deps(false),
            waiting_for_execstat(false), start_explicit(false),
            prop_require(false), prop_release(false), prop_failure(false),
            force_stop(false)
    {
        service_set = set;
        service_name = name;
        service_type = ServiceType::DUMMY;
    }
    
    ServiceRecord(ServiceSet *set, string name, ServiceType service_type, string &&command, std::list<std::pair<unsigned,unsigned>> &command_offsets,
            sr_list * pdepends_on, sr_list * pdepends_soft)
        : ServiceRecord(set, name)
    {
        service_set = set;
        service_name = name;
        this->service_type = service_type;
        this->depends_on = std::move(*pdepends_on);

        program_name = std::move(command);
        exec_arg_parts = separate_args(program_name, command_offsets);

        for (sr_iter i = depends_on.begin(); i != depends_on.end(); ++i) {
            (*i)->dependents.push_back(this);
        }

        // Soft dependencies
        auto b_iter = soft_deps.end();
        for (sr_iter i = pdepends_soft->begin(); i != pdepends_soft->end(); ++i) {
            b_iter = soft_deps.emplace(b_iter, this, *i);
            (*i)->soft_dpts.push_back(&(*b_iter));
            ++b_iter;
        }
    }
    
    virtual ~ServiceRecord() noexcept
    {
    }
    
    // begin transition from stopped to started state or vice versa depending on current and desired state
    void execute_transition() noexcept;
    
    void do_propagation() noexcept;
    
    // Called on transition of desired state from stopped to started (or unpinned stop)
    void do_start() noexcept;

    // Called on transition of desired state from started to stopped (or unpinned start)
    void do_stop() noexcept;
    
    // Console is available.
    void acquiredConsole() noexcept;
    
    // Set the stop command and arguments (may throw std::bad_alloc)
    void setStopCommand(std::string command, std::list<std::pair<unsigned,unsigned>> &stop_command_offsets)
    {
        stop_command = command;
        stop_arg_parts = separate_args(stop_command, stop_command_offsets);
    }
    
    // Get the current service state.
    ServiceState getState() noexcept
    {
        return service_state;
    }
    
    // Get the target (aka desired) state.
    ServiceState getTargetState() noexcept
    {
        return desired_state;
    }

    // Set logfile, should be done before service is started
    void setLogfile(string logfile)
    {
        this->logfile = logfile;
    }
    
    // Set whether this service should automatically restart when it dies
    void setAutoRestart(bool auto_restart) noexcept
    {
        this->auto_restart = auto_restart;
    }
    
    void setSmoothRecovery(bool smooth_recovery) noexcept
    {
        this->smooth_recovery = smooth_recovery;
    }
    
    // Set "on start" flags (commands)
    void setOnstartFlags(OnstartFlags flags) noexcept
    {
        this->onstart_flags = flags;
    }
    
    // Set an additional signal (other than SIGTERM) to be used to terminate the process
    void setExtraTerminationSignal(int signo) noexcept
    {
        this->term_signal = signo;
    }
    
    void set_pid_file(string &&pid_file) noexcept
    {
        this->pid_file = std::move(pid_file);
    }
    
    void set_socket_details(string &&socket_path, int socket_perms, uid_t socket_uid, uid_t socket_gid) noexcept
    {
        this->socket_path = std::move(socket_path);
        this->socket_perms = socket_perms;
        this->socket_uid = socket_uid;
        this->socket_gid = socket_gid;
    }

    const std::string &getServiceName() const noexcept { return service_name; }
    ServiceState getState() const noexcept { return service_state; }
    
    void start(bool activate = true) noexcept;  // start the service
    void stop(bool bring_down = true) noexcept;   // stop the service
    
    void forceStop() noexcept; // force-stop this service and all dependents
    
    // Pin the service in "started" state (when it reaches the state)
    void pinStart() noexcept
    {
        pinned_started = true;
    }
    
    // Pin the service in "stopped" state (when it reaches the state)
    void pinStop() noexcept
    {
        pinned_stopped = true;
    }
    
    // Remove both "started" and "stopped" pins. If the service is currently pinned
    // in either state but would naturally be in the opposite state, it will immediately
    // commence starting/stopping.
    void unpin() noexcept;
    
    bool isDummy() noexcept
    {
        return service_type == ServiceType::DUMMY;
    }
    
    // Add a listener. A listener must only be added once. May throw std::bad_alloc.
    void addListener(ServiceListener * listener)
    {
        listeners.insert(listener);
    }
    
    // Remove a listener.    
    void removeListener(ServiceListener * listener) noexcept
    {
        listeners.erase(listener);
    }
};

class base_process_service : public ServiceRecord
{
    friend class ServiceChildWatcher;
    friend class ServiceIoWatcher;

    protected:
    ServiceChildWatcher child_listener;
    ServiceIoWatcher child_status_listener;

    // start the process, return true on success
    virtual bool start_ps_process() noexcept;
    bool start_ps_process(const std::vector<const char *> &args, bool on_console) noexcept;

    virtual void all_deps_stopped() noexcept;
    virtual void handle_exit_status(int exit_status) noexcept = 0;

    public:
    base_process_service(ServiceSet *sset, string name, ServiceType service_type, string &&command,
            std::list<std::pair<unsigned,unsigned>> &command_offsets,
            sr_list * pdepends_on, sr_list * pdepends_soft)
         : ServiceRecord(sset, name, service_type, std::move(command), command_offsets,
             pdepends_on, pdepends_soft), child_listener(this), child_status_listener(this)
    {
    }

    ~base_process_service() noexcept
    {
    }
};

class process_service : public base_process_service
{
    // called when the process exits. The exit_status is the status value yielded by
    // the "wait" system call.
    virtual void handle_exit_status(int exit_status) noexcept override;

    public:
    process_service(ServiceSet *sset, string name, string &&command,
            std::list<std::pair<unsigned,unsigned>> &command_offsets,
            sr_list * pdepends_on, sr_list * pdepends_soft)
         : base_process_service(sset, name, ServiceType::PROCESS, std::move(command), command_offsets,
             pdepends_on, pdepends_soft)
    {
    }

    ~process_service() noexcept
    {
    }
};

class bgproc_service : public base_process_service
{
    virtual void handle_exit_status(int exit_status) noexcept override;

    bool doing_recovery : 1;    // if we are currently recovering a BGPROCESS (restarting process, while
                                //   holding STARTED service state)

    // Read the pid-file, return false on failure
    bool read_pid_file() noexcept;

    public:
    bgproc_service(ServiceSet *sset, string name, string &&command,
            std::list<std::pair<unsigned,unsigned>> &command_offsets,
            sr_list * pdepends_on, sr_list * pdepends_soft)
         : base_process_service(sset, name, ServiceType::BGPROCESS, std::move(command), command_offsets,
             pdepends_on, pdepends_soft)
    {
        doing_recovery = false;
    }

    ~bgproc_service() noexcept
    {
    }
};

class scripted_service : public base_process_service
{
    virtual void all_deps_stopped() noexcept override;
    virtual void handle_exit_status(int exit_status) noexcept override;

    public:
    scripted_service(ServiceSet *sset, string name, string &&command,
            std::list<std::pair<unsigned,unsigned>> &command_offsets,
            sr_list * pdepends_on, sr_list * pdepends_soft)
         : base_process_service(sset, name, ServiceType::SCRIPTED, std::move(command), command_offsets,
             pdepends_on, pdepends_soft)
    {
    }

    ~scripted_service() noexcept
    {
    }
};


/*
 * A ServiceSet, as the name suggests, manages a set of services.
 *
 * Other than the ability to find services by name, the service set manages various queues.
 * One is the queue for processes wishing to acquire the console. There is also a set of
 * processes that want to start, and another set of those that want to stop. These latter
 * two "queues" (not really queues since their order is not important) are used to prevent too
 * much recursion and to prevent service states from "bouncing" too rapidly.
 * 
 * A service that wishes to start or stop puts itself on the start/stop queue; a service that
 * needs to propagate changes to dependent services or dependencies puts itself on the
 * propagation queue. Any operation that potentially manipulates the queues must be followed
 * by a "process queues" order (processQueues() method).
 *
 * Note that processQueues always repeatedly processes both queues until they are empty. The
 * process is finite because starting a service can never cause services to stop, unless they
 * fail to start, which should cause them to stop semi-permanently.
 */
class ServiceSet
{
    int active_services;
    std::list<ServiceRecord *> records;
    const char *service_dir;  // directory containing service descriptions
    bool restart_enabled; // whether automatic restart is enabled (allowed)
    
    ShutdownType shutdown_type = ShutdownType::CONTINUE;  // Shutdown type, if stopping
    
    ServiceRecord * console_queue_head = nullptr; // first record in console queue
    ServiceRecord * console_queue_tail = nullptr; // last record in console queue

    // Propagation and start/stop "queues" - list of services waiting for processing
    ServiceRecord * first_prop_queue = nullptr;
    ServiceRecord * first_stop_queue = nullptr;
    
    // Private methods
        
    // Load a service description, and dependencies, if there is no existing
    // record for the given name.
    // Throws:
    //   ServiceLoadException (or subclass) on problem with service description
    //   std::bad_alloc on out-of-memory condition
    ServiceRecord *loadServiceRecord(const char *name);

    // Public
    
    public:
    ServiceSet(const char *service_dir)
    {
        this->service_dir = service_dir;
        active_services = 0;
        restart_enabled = true;
    }
    
    // Start the service with the given name. The named service will begin
    // transition to the 'started' state.
    //
    // Throws a ServiceLoadException (or subclass) if the service description
    // cannot be loaded or is invalid;
    // Throws std::bad_alloc if out of memory.
    void startService(const char *name);
    
    // Locate an existing service record.
    ServiceRecord *find_service(const std::string &name) noexcept;
    
    // Find a loaded service record, or load it if it is not loaded.
    // Throws:
    //   ServiceLoadException (or subclass) on problem with service description
    //   std::bad_alloc on out-of-memory condition 
    ServiceRecord *loadService(const std::string &name)
    {
        ServiceRecord *record = find_service(name);
        if (record == nullptr) {
            record = loadServiceRecord(name.c_str());
        }
        return record;
    }
    
    // Get the list of all loaded services.
    const std::list<ServiceRecord *> &listServices()
    {
        return records;
    }
    
    // Stop the service with the given name. The named service will begin
    // transition to the 'stopped' state.
    void stopService(const std::string &name) noexcept;
    
    // Add a service record to the state propogation queue
    void addToPropQueue(ServiceRecord *service) noexcept
    {
        if (service->next_in_prop_queue == nullptr && first_prop_queue != service) {
            service->next_in_prop_queue = first_prop_queue;
            first_prop_queue = service;
        }
    }
    
    // Add a service record to the start queue; called by service record
    void addToStartQueue(ServiceRecord *service) noexcept
    {
        // The start/stop queue is actually one queue:
        addToStopQueue(service);
    }
    
    // Add a service to the stop queue; called by service record
    void addToStopQueue(ServiceRecord *service) noexcept
    {
        if (service->next_in_stop_queue == nullptr && first_stop_queue != service) {
            service->next_in_stop_queue = first_stop_queue;
            first_stop_queue = service;
        }
    }
    
    // Process state propagation and start/stop queues, until they are empty.
    // TODO remove the pointless parameter
    void processQueues(bool ignoredparam = false) noexcept
    {
        while (first_stop_queue != nullptr || first_prop_queue != nullptr) {
            while (first_prop_queue != nullptr) {
                auto next = first_prop_queue;
                first_prop_queue = next->next_in_prop_queue;
                next->next_in_prop_queue = nullptr;
                next->do_propagation();
            }
            while (first_stop_queue != nullptr) {
                auto next = first_stop_queue;
                first_stop_queue = next->next_in_stop_queue;
                next->next_in_stop_queue = nullptr;
                next->execute_transition();
            }
        }
    }
    
    // Set the console queue tail (returns previous tail)
    ServiceRecord * append_console_queue(ServiceRecord * newTail) noexcept
    {
        auto prev_tail = console_queue_tail;
        console_queue_tail = newTail;
        newTail->next_for_console = nullptr;
        if (! prev_tail) {
            console_queue_head = newTail;
            enable_console_log(false);
        }
        else {
            prev_tail->next_for_console = newTail;
        }
        return prev_tail;
    }
    
    // Retrieve the current console queue head and remove it from the queue
    ServiceRecord * pullConsoleQueue() noexcept
    {
        auto prev_head = console_queue_head;
        if (prev_head) {
            prev_head->acquiredConsole();
            console_queue_head = prev_head->next_for_console;
            if (! console_queue_head) {
                console_queue_tail = nullptr;
            }
        }
        else {
            enable_console_log(true);
        }
        return prev_head;
    }
    
    // Notification from service that it is active (state != STOPPED)
    // Only to be called on the transition from inactive to active.
    void service_active(ServiceRecord *) noexcept;
    
    // Notification from service that it is inactive (STOPPED)
    // Only to be called on the transition from active to inactive.
    void service_inactive(ServiceRecord *) noexcept;
    
    // Find out how many services are active (starting, running or stopping,
    // but not stopped).
    int count_active_services() noexcept
    {
        return active_services;
    }
    
    void stop_all_services(ShutdownType type = ShutdownType::HALT) noexcept
    {
        restart_enabled = false;
        shutdown_type = type;
        for (std::list<ServiceRecord *>::iterator i = records.begin(); i != records.end(); ++i) {
            (*i)->stop(false);
            (*i)->unpin();
        }
        processQueues(false);
    }
    
    void set_auto_restart(bool restart) noexcept
    {
        restart_enabled = restart;
    }
    
    bool get_auto_restart() noexcept
    {
        return restart_enabled;
    }
    
    ShutdownType getShutdownType() noexcept
    {
        return shutdown_type;
    }
};

#endif