c++ - DBUS 代码在放置在守护程序进程中时会崩溃，但在没有守护程序代码的独立 main() 函数中运行良好

Question

我在 Ubuntu 中运行了以下代码。 DBUS 代码在放置在守护进程 while 进程中时会崩溃，但在没有守护进程肉鸡板代码结构的独立独立 main() 函数中运行良好。注意:一旦解决了问题，我将在类结构中重构代码。

以下代码崩溃。

//file3=giommdaemontest
//g++ -g -std=c++0x $(file3).cc -o $(file3) `pkg-config --libs --cflags giomm-2.4`


/* Copyright (C) 2011 The giomm Development Team
 * Copyright (C) 2013 enthusiasticgeek (Demo for StackOverflow)
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/* This is a basic server providing a clock like functionality.  Clients can
 * get the current time, set the alarm and get notified when the alarm time is
 * reached.  It is basic because there is only one global alarm which any
 * client can set.  Clients listening for the alarm signal will be notified by
 * use of the global alarm signal.  The server should be easily modifiable to
 * allow per-client alarms, but that is left as an exercise.
 *
 * Along with the above it provides a method to get its stdout's file
 * descriptor to test the Gio::DBus::Message API.
 */

#include <giomm.h>
#include <glibmm.h>
#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>

namespace
{

static Glib::RefPtr<Gio::DBus::NodeInfo> introspection_data;

static Glib::ustring introspection_xml =
  "<node>"
  "  <interface name='enthusiasticgeek.test.DBus'>"
  "    <method name='GetTime'>"
  "      <arg type='s' name='iso8601' direction='out'/>"
  "    </method>"
  "    <method name='ParamFunction'>"  
  "      <arg type='s' name='param1' direction='in'/>"
  "      <arg type='s' name='param2' direction='in'/>"
  "      <arg type='s' name='param3' direction='out'/>"
  "      <arg type='s' name='param4' direction='out'/>"
  "    </method>"
 // The time of the alarm as an iso8601 string.
//  "    <property type='s' name='myproperty' access='readwrite'/>"
  "    <signal name='EventOccurred'>"
  "      <arg type='s' name='some_string'/>"
  "    </signal> "
  "  </interface>"
  "</node>";

guint registered_id = 0;

// Stores the current alarm.
static Glib::TimeVal curr_alarm;

Glib::RefPtr<Gio::DBus::Connection> m_connection;
  const char *m_path;
  const char *m_interface_name;

} // anonymous namespace

void emit_signal(const Glib::ustring & name, const Glib::VariantContainerBase & parameters)
{
     GError *error;
     error = NULL;
   /*  g_dbus_connection_emit_signal (connection,
                                 NULL,
                                 "/org/gtk/GDBus/PeerTestObject",
                                 "org.gtk.GDBus.PeerTestInterface",
                                 "PeerSignal",
                                 NULL,
                                 &error);  */
  //work-around glibmm bug 645072
  if( (m_connection) && (m_path) && (m_interface_name)){
    std::cout << "info is " << m_connection << " and " << m_path << " and " << m_interface_name << std::endl;
    g_dbus_connection_emit_signal(m_connection->gobj(), NULL, m_path, m_interface_name, name.c_str(),
                              const_cast<GVariant*>(parameters.gobj()), &error);
  }
}

void EventOccurred(const std::string & some_string)
{
  emit_signal("EventOccurred", Glib::VariantContainerBase::create_tuple(Glib::Variant<Glib::ustring>::create(some_string)));
}

static void on_method_call(const Glib::RefPtr<Gio::DBus::Connection>& conn /* connection */,
  const Glib::ustring& sender /* sender */, const Glib::ustring& path/* object_path */,
  const Glib::ustring& interface/* interface_name */, const Glib::ustring& method_name,
  const Glib::VariantContainerBase& parameters,
  const Glib::RefPtr<Gio::DBus::MethodInvocation>& invocation)
{

  m_connection = conn;
  m_path = path.c_str();
  m_interface_name = interface.c_str();

  if(method_name == "GetTime")
  {
    std::cout << "GetTime function" << std::endl;
    std::cout << "test this function" << std::endl;
    Glib::TimeVal curr_time;
    curr_time.assign_current_time();

    const Glib::ustring time_str = curr_time.as_iso8601();
    const Glib::Variant<Glib::ustring> time_var =
    Glib::Variant<Glib::ustring>::create(time_str);

    // Create the tuple.
    Glib::VariantContainerBase response =
    Glib::VariantContainerBase::create_tuple(time_var);

    // Return the tuple with the included time.
    invocation->return_value(response);
  }
  else if(method_name == "ParamFunction")
  {
    // Get the parameter tuple.
    Glib::Variant<Glib::ustring> param1;
    Glib::Variant<Glib::ustring> param2;

   if(parameters.get_n_children() == 2) {
        parameters.get_child(param1, 0);
        parameters.get_child(param2, 1);
    }

    // Get the strings.
    const Glib::ustring param1_str = param1.get();
    std::cout << "received data param[0]" << param1_str << std::endl;
    const Glib::ustring param2_str = param2.get();
    std::cout << "received data param[1]" << param2_str << std::endl;

    std::string string1 = " Ok I received the name.";
    std::string string2 = " Ok I received the profession.";
    std::vector<Glib::VariantBase> parameters_response;
    parameters_response.reserve(2); ;
    parameters_response.push_back(Glib::Variant<Glib::ustring>::create(string1));
    parameters_response.push_back(Glib::Variant<Glib::ustring>::create(string2));
    Glib::VariantContainerBase params_response = Glib::VariantContainerBase::create_tuple(parameters_response);

    invocation->return_value(params_response);

/*
    if(!curr_alarm.assign_from_iso8601(time_str))
    {
      // If setting alarm was not successful, return an error.
      Gio::DBus::Error error(Gio::DBus::Error::INVALID_ARGS,
      "Alarm string is not in ISO8601 format.");
      invocation->return_error(error);
    }
*/
  }
  else
  {
    // Non-existent method on the interface.
    Gio::DBus::Error error(Gio::DBus::Error::UNKNOWN_METHOD,
      "Method does not exist.");
    invocation->return_error(error);
  }
}

//This must be a global instance. See the InterfaceVTable documentation.
//TODO: Make that unnecessary.
const Gio::DBus::InterfaceVTable interface_vtable(sigc::ptr_fun(&on_method_call));

void on_bus_acquired(const Glib::RefPtr<Gio::DBus::Connection>& connection, const Glib::ustring& /* name */)
{
  // Export an object to the bus:

  // See https://bugzilla.gnome.org/show_bug.cgi?id=646417 about avoiding
  // the repetition of the interface name:
  try
  {
    registered_id = connection->register_object("/enthusiasticgeek/test/DBus",
      introspection_data->lookup_interface(),
      interface_vtable);
  }
  catch(const Glib::Error& ex)
  {
    std::cerr << "Registration of object failed." << std::endl;
  }

  return;
}

void on_name_acquired(const Glib::RefPtr<Gio::DBus::Connection>& /* connection */, const Glib::ustring& /* name */)
{
  //TODO: What is this good for? See https://bugzilla.gnome.org/show_bug.cgi?id=646427
}

void on_name_lost(const Glib::RefPtr<Gio::DBus::Connection>& connection, const Glib::ustring& /* name */)
{
  connection->unregister_object(registered_id);
}

void on_get_property(Glib::VariantBase& property,
  const Glib::RefPtr<Gio::DBus::Connection>& /* connection */,
  const Glib::ustring& /* sender */, const Glib::ustring& /* object_path */,
  const Glib::ustring& /* interface_name */, const Glib::ustring& property_name)
{
  if(property_name == "myproperty")
  {
    if(curr_alarm.valid())
    {
      std::cout << "property is called " << std::endl;
      //Glib::ustring alarm_str = curr_alarm.as_iso8601();

      //Glib::Variant<Glib::ustring> alarm_var =
      //  Glib::Variant<Glib::ustring>::create(alarm_str);

      //property = alarm_var;
    }
    else
    {
      throw Gio::Error(Gio::Error::FAILED, "Property has not been set.");
    }
  }
  else
  {
    throw Gio::DBus::Error(Gio::DBus::Error::FAILED, "Unknown property name.");
  }
}

/** TODO: This code does not seem to be used. murrayc.
bool on_set_property(const Glib::RefPtr<Gio::DBus::Connection>& connection,
  const Glib::ustring& sender, const Glib::ustring& object_path,
  const Glib::ustring& interface_name, const Glib::ustring& property_name,
  const Glib::VariantBase& value)
{
  if(property_name == "myproperty")
  {
  }
  else
  {
  }
}
*/
bool TimeoutCheck()
{
    std::cout << "Checking for timeout ..." << std::endl;
    EventOccurred(" <<< Timeout Event has occurred >>>");
    return true;
}
int main(int, char**)
{

    /* Our process ID and Session ID */
    pid_t pid, sid;

    /* Fork off the parent process */
    pid = fork();
    if (pid < 0) {
            exit(EXIT_FAILURE);
    }
    /* If we got a good PID, then
       we can exit the parent process. */
    if (pid > 0) {
            exit(EXIT_SUCCESS);
    }

    /* Change the file mode mask */
    umask(0);

    /* Open any logs here */        

    /* Create a new SID for the child process */
    sid = setsid();
    if (sid < 0) {
            /* Log the failure */
            exit(EXIT_FAILURE);
    }



    /* Change the current working directory */
    if ((chdir("/")) < 0) {
            /* Log the failure */
            exit(EXIT_FAILURE);
    }

    /* Close out the standard file descriptors */
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);

    /* Daemon-specific initialization goes here */


    while(1){
      std::locale::global(std::locale(""));
      Gio::init();

     try
      {
        introspection_data = Gio::DBus::NodeInfo::create_for_xml(introspection_xml);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "Unable to create introspection data: " << ex.what() <<
          "." << std::endl;
        return 1;
      }

      const guint id = Gio::DBus::own_name(Gio::DBus::BUS_TYPE_SESSION,
        "enthusiasticgeek.test.DBus",
        sigc::ptr_fun(&on_bus_acquired),
        sigc::ptr_fun(&on_name_acquired),
        sigc::ptr_fun(&on_name_lost));

      //create timeout signal
       static const unsigned delayInMillis = 5000;

        sigc::slot<bool> tslot = sigc::ptr_fun(&TimeoutCheck);
        Glib::signal_timeout().connect(tslot, delayInMillis);

      //Keep the service running until the process is killed:
      Glib::RefPtr<Glib::MainLoop> loop = Glib::MainLoop::create();
      loop->run();

      Gio::DBus::unown_name(id);
    }

  return EXIT_SUCCESS;
}

但是以下工作正常

int main(int, char**)
{



    //while(1){
      std::locale::global(std::locale(""));
      Gio::init();

     try
      {
        introspection_data = Gio::DBus::NodeInfo::create_for_xml(introspection_xml);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "Unable to create introspection data: " << ex.what() <<
          "." << std::endl;
        return 1;
      }

      const guint id = Gio::DBus::own_name(Gio::DBus::BUS_TYPE_SESSION,
        "enthusiasticgeek.test.DBus",
        sigc::ptr_fun(&on_bus_acquired),
        sigc::ptr_fun(&on_name_acquired),
        sigc::ptr_fun(&on_name_lost));

      //create timeout signal
       static const unsigned delayInMillis = 5000;

        sigc::slot<bool> tslot = sigc::ptr_fun(&TimeoutCheck);
        Glib::signal_timeout().connect(tslot, delayInMillis);

      //Keep the service running until the process is killed:
      Glib::RefPtr<Glib::MainLoop> loop = Glib::MainLoop::create();
      loop->run();

      Gio::DBus::unown_name(id);
    //}

  return EXIT_SUCCESS;
}

Answer 1

好的，这段代码中的一些调整有助于正确运行代码

    ...
    pid_t pid, sid;
    static int pipefd[2];

    pid = fork();
    if (pid < 0) {  //error
            close(pipefd[0]);
            close(pipefd[1]);
            exit(EXIT_FAILURE);
    }
    if (pid > 0) {  //parent process
            close(pipefd[1]); //close write/ output 
            printf("%d\n", pid);
            char buf[32];
            while (read(pipefd[0], buf, sizeof(buf)) > 0) {
                   printf("%s", buf);
            }
            printf("\n");
            close(pipefd[0]); //close read/ input
            exit(EXIT_SUCCESS);
    }
        // running as the child, continue daemonizing
    close(pipefd[0]);
    umask(0);
    ...