Changes between Version 15 and Version 16 of Processing/lagdevelopersfaq


Ignore:
Timestamp:
Jul 9, 2012 12:12:41 PM (7 years ago)
Author:
jaho
Comment:

--

Legend:

Unmodified
Added
Removed
Modified
  • Processing/lagdevelopersfaq

    v15 v16  
    2929[#q4.4 4.4 How does saving of files work?] \\
    3030[#q4.5 4.5 How is LAS 1.3 point format handled?] \\
    31 [#q4.6 4.6 How does rendering work?] \\
     31[#q4.6 4.6 How is threading done?] \\
     32[#q4.7 4.7 How does rendering work?] \\
    3233
    3334[#q5 5. Further Development] \\
     
    395396Finally we copy over the waveform data manually  and attach it to the end of the output file. Note that this requires for LAS 1.3 files to be saved to a separate file after modification. Unfortunately there is no way around this with how laslib library currently works.
    396397
    397 === 4.6 How does rendering work? [=#q4.6] ===
     398=== 4.6 How is threading done? [=#q4.6] ===
     399
     400It uses [http://developer.gnome.org/glib/2.30/glib-Threads.html Gtkmm threading system] and implements worker classes which do the work in separate threads, without blocking the GUI. All worker classes inherit from {{{Worker.h}}} which is pretty simple. It provides a {{{start()}}} method with launches a new thread and a virtual {{{run()}}} method with code to be executed. It also has a {{{Glib::Dispatcher}}} object for inter-thread communication (works like signals).
     401
     402{{{
     403#!div style="font-size: 100%"
     404  {{{#!c++
     405  class Worker
     406  {
     407  public:
     408        Worker() : thread(0), stopped(false) {}
     409
     410        virtual ~Worker()
     411        {
     412                {
     413                        Glib::Mutex::Lock lock (mutex);
     414                        stopped = true;
     415                }
     416                if (thread)
     417                        thread->join();
     418        }
     419
     420        void start()
     421        {
     422                thread = Glib::Thread::create(sigc::mem_fun(*this, &Worker::run), true);
     423        }
     424
     425        Glib::Dispatcher sig_done;
     426
     427  protected:
     428        virtual void run() = 0;
     429
     430        Glib::Thread* thread;
     431        Glib::Mutex mutex;
     432        bool stopped;
     433  };
     434  }}}
     435}}}
     436
     437Each GUI class which uses threads has a {{{Worker}}} member initially set to null. Then once a function that starts the work is called the worker is created and started, and signal handlers are connected to handle the {{{Dispatcher}}} objects:
     438
     439{{{
     440#!div style="font-size: 100%"
     441  {{{#!c++
     442  // Check if we don't already have a thread running
     443  if (worker != NULL) return;
     444
     445  // Create a new worker
     446  worker = new Worker(...)
     447  // Start the worker
     448  worker->start()
     449  // Connect signals
     450  worker->sig_done().connect(sigc::mem_fun(*this, &GUIClass::on_worker_work_finished));
     451
     452  // Display a progress bar or a busy cursor
     453  }}}
     454}}}
     455
     456Once the worker has finished it emits {{{sig_done()}}} signal in its {{{run()}}} method notifying the caller class and {{{on_worker_work_finished()}}} method gets called. Most worker classes implement more signals to notify about different events (for example load progress to move the progress bar). The idea stays the same though. \\ \\
     457Additionally in GUI classes {{{Glib::Mutex}}} objects are used at the beginning of each critical section to avoid race conditions. Using brackets around the section makes sure that the {{{Mutex::Lock}}} object get automatically destroyed.
     458
     459{{{
     460#!div style="font-size: 100%"
     461  {{{#!c++
     462  // some non critical code
     463
     464  {
     465    Glib::Mutex::Lock lock (mutex)  // mutex is a class member
     466    // critical code
     467  }  // lock gets destroyed here 
     468  }}}
     469}}}
     470
     471=== 4.7 How does rendering work? [=#q4.7] ===
    398472
    399473It's difficult to tell. It's quite a mess and it definitely needs some refactoring for maintainability. It does work however so I haven't changed it, focusing on other things. \\ \\