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# thread/dispatcher.cc

A Glib::Dispatcher example.

    /*
     * Glib::Dispatcher example -- cross thread signalling
     * by Daniel Elstner  <daniel.kitta@gmail.com>
     *
     * modified to only use glibmm
     * by J. Abelardo Gutierrez <jabelardo@cantv.net>
     *
     * Copyright (c) 2002-2003  Free Software Foundation
     */

    #include <glibmm.h>

    #include <algorithm>
    #include <functional>
    #include <iostream>
    #include <vector>

    namespace
    {

    /*
     * Note that it does not make sense for this class to inherit from
     * sigc::trackable, as doing so would only give a false sense of security.
     * Once the thread launch has been triggered, the object has to stay alive
     * until the thread has been joined again.  The code running in the thread
     * assumes the existence of the object.  If it is destroyed earlier, the
     * program will crash, with sigc::trackable or without it.
     */
    class ThreadProgress
    {
    public:
      explicit ThreadProgress(int id);
      virtual ~ThreadProgress();

      int  id() const;
      void launch();
      void join();
      bool unfinished() const;

      sigc::signal<void>& signal_finished();

    private:
      enum { ITERATIONS = 100 };

      // Note that the thread does not write to the member data at all.  It only
      // reads signal_increment_, which is only written to before the thread is
      // lauched.  Therefore, no locking is required.
      Glib::Thread*       thread_;
      int                 id_;
      unsigned int        progress_;
      Glib::Dispatcher    signal_increment_;
      sigc::signal<void>  signal_finished_;

      void progress_increment();
      void thread_function();
    };

    class Application : public sigc::trackable
    {
    public:
      Application();
      virtual ~Application();

      void run();

    private:
      Glib::RefPtr<Glib::MainLoop>  main_loop_;
      std::vector<ThreadProgress*>  progress_threads_;

      void launch_threads();
      void on_progress_finished(ThreadProgress* thread_progress);
    };

    template <class T>
    class DeletePtr : public std::unary_function<void, T>
    {
    public:
      void operator()(T ptr) const { delete ptr; }
    };

    ThreadProgress::ThreadProgress(int id)
    :
      thread_   (0),
      id_       (id),
      progress_ (0)
    {
      // Connect to the cross-thread signal.
      signal_increment_.connect(sigc::mem_fun(*this, &ThreadProgress::progress_increment));
    }

    ThreadProgress::~ThreadProgress()
    {
      // It is an error if the thread is still running at this point.
      g_return_if_fail(thread_ == 0);
    }

    int ThreadProgress::id() const
    {
      return id_;
    }

    void ThreadProgress::launch()
    {
      // Create a joinable thread.
      thread_ = Glib::Thread::create(sigc::mem_fun(*this, &ThreadProgress::thread_function), true);
    }

    void ThreadProgress::join()
    {
      thread_->join();
      thread_ = 0;
    }

    bool ThreadProgress::unfinished() const
    {
      return (progress_ < ITERATIONS);
    }

    sigc::signal<void>& ThreadProgress::signal_finished()
    {
      return signal_finished_;
    }

    void ThreadProgress::progress_increment()
    {
      ++progress_;
      std::cout << "Thread " << id_ << ": " << progress_ << '%' << std::endl;

      if (progress_ >= ITERATIONS)
        signal_finished_();
    }

    void ThreadProgress::thread_function()
    {
      Glib::Rand rand;

      for (int i = 0; i < ITERATIONS; ++i)
      {
        Glib::usleep(rand.get_int_range(2000, 20000));

        // Tell the main thread to increment the progress value.
        signal_increment_();
      }
    }

    Application::Application()
    :
      main_loop_        (Glib::MainLoop::create()),
      progress_threads_ (5)
    {
      // Note that unless you're targetting an embedded platform, you can assume
      // exceptions to be enabled.  The #ifdef is only here to make the example
      // compile in either case; you may ignore it otherwise.
    #ifdef GLIBMM_EXCEPTIONS_ENABLED
      try
    #endif
      {
        for (std::vector<ThreadProgress*>::size_type i = 0; i < progress_threads_.size(); ++i)
        {
          ThreadProgress *const progress = new ThreadProgress(i + 1);
          progress_threads_[i] = progress;

          progress->signal_finished().connect(
              sigc::bind<1>(sigc::mem_fun(*this, &Application::on_progress_finished), progress));
        }
      }
    #ifdef GLIBMM_EXCEPTIONS_ENABLED
      catch (...)
      {
        // In your own code, you should preferably use a smart pointer
        // to ensure exception safety.
        std::for_each(progress_threads_.begin(), progress_threads_.end(),
                      DeletePtr<ThreadProgress*>());
        throw;
      }
    #endif
    }

    Application::~Application()
    {
      std::for_each(progress_threads_.begin(), progress_threads_.end(),
                    DeletePtr<ThreadProgress*>());
    }

    void Application::run()
    {
      // Install a one-shot idle handler to launch the threads.
      Glib::signal_idle().connect(
          sigc::bind_return(sigc::mem_fun(*this, &Application::launch_threads), false));

      main_loop_->run();
    }

    void Application::launch_threads()
    {
      std::cout << "Launching " << progress_threads_.size() << " threads:" << std::endl;

      std::for_each(progress_threads_.begin(), progress_threads_.end(),
                    std::mem_fun(&ThreadProgress::launch));
    }

    void Application::on_progress_finished(ThreadProgress* thread_progress)
    {
      thread_progress->join();

      std::cout << "Thread " << thread_progress->id() << ": finished." << std::endl;

      // Quit if it was the last thread to be joined.
      if (std::find_if(progress_threads_.begin(), progress_threads_.end(),
                       std::mem_fun(&ThreadProgress::unfinished)) == progress_threads_.end())
      {
        main_loop_->quit();
      }
    }

    } // anonymous namespace

    int main(int, char**)
    {
      Glib::thread_init();

      Application application;
      application.run();

      return 0;
    }