my_dll.cpp

/////////////////////////////////////////////////////////////////////////////
// Name:        my_dll.cpp
// Purpose:     Sample showing how to use wx from a DLL
// Author:      Vaclav Slavik
// Created:     2009-12-03
// Copyright:   (c) 2009 Vaclav Slavik
// Licence:     wxWindows licence
/////////////////////////////////////////////////////////////////////////////

// ============================================================================
// declarations
// ============================================================================

// ----------------------------------------------------------------------------
// headers
// ----------------------------------------------------------------------------

#include "wx/wxprec.h"

#include "wx/app.h"
#include "wx/dynlib.h"
#include "wx/frame.h"
#include "wx/panel.h"
#include "wx/sizer.h"
#include "wx/stattext.h"
#include "wx/button.h"
#include "wx/thread.h"
#include "wx/msgdlg.h"

#include <pthread.h>

#include "my_dll.h"

// ----------------------------------------------------------------------------
// GUI classes
// ----------------------------------------------------------------------------

class MyDllFrame : public wxFrame
{
public:
  MyDllFrame(wxWindow *parent, const wxString& label);

  void OnAbout(wxCommandEvent& event);

  DECLARE_EVENT_TABLE()
};


static const int CMD_SHOW_WINDOW = wxNewId();
static const int CMD_TERMINATE = wxNewId();

class MyDllApp : public wxApp
{
public:
  MyDllApp();

private:
  void OnShowWindow(wxThreadEvent& event);
  void OnTerminate(wxThreadEvent& event);
};


// ============================================================================
// implementation
// ============================================================================

// ----------------------------------------------------------------------------
// MyDllFrame
// ----------------------------------------------------------------------------

BEGIN_EVENT_TABLE(MyDllFrame, wxFrame)
EVT_BUTTON(wxID_ABOUT, MyDllFrame::OnAbout)
END_EVENT_TABLE()

MyDllFrame::MyDllFrame(wxWindow *parent, const wxString& label)
: wxFrame(parent, wxID_ANY, label)
{
  wxPanel *p = new wxPanel(this, wxID_ANY);
  wxSizer *sizer = new wxBoxSizer(wxVERTICAL);

  sizer->Add
    (
     new wxStaticText
     (
      p, wxID_ANY,
      wxString::Format
      (
       "Running using %s\n"
       "wxApp instance is %p, thread ID %ld",
       wxVERSION_STRING,
       wxApp::GetInstance(),
       wxThread::GetCurrentId()
       )
      ),
     wxSizerFlags(1).Expand().Border(wxALL, 10)
     );

  sizer->Add
    (
     new wxButton(p, wxID_ABOUT, "Show info"),
     wxSizerFlags(0).Right().Border(wxALL, 10)
     );

  p->SetSizerAndFit(sizer);

  wxSizer *fsizer = new wxBoxSizer(wxVERTICAL);
  fsizer->Add(p, wxSizerFlags(1).Expand());
  SetSizerAndFit(fsizer);
}

void MyDllFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
{
  wxMessageBox("This window is running in its own thread,\n"
           "using private wxWidgets instance compiled into the DLL.",
           "About",
           wxOK | wxICON_INFORMATION);
}


// ----------------------------------------------------------------------------
// MyDllApp
// ----------------------------------------------------------------------------

MyDllApp::MyDllApp()
{
  // Keep the wx "main" thread running even without windows. This greatly
  // simplifies threads handling, because we don't have to correctly
  // implement wx-thread restarting.
  //
  // Note that this only works if you don't explicitly call ExitMainLoop(),
  // except in reaction to wx_dll_cleanup()'s message. wx_dll_cleanup()
  // relies on the availability of wxApp instance and if the event loop
  // terminated, wxEntry() would return and wxApp instance would be
  // destroyed.
  //
  // Also note that this is efficient, because if there are no windows, the
  // thread will sleep waiting for a new event. We could safe some memory
  // by shutting the thread down when it's no longer needed, though.
  SetExitOnFrameDelete(false);

  Connect(CMD_SHOW_WINDOW,
      wxEVT_THREAD,
      wxThreadEventHandler(MyDllApp::OnShowWindow));
  Connect(CMD_TERMINATE,
      wxEVT_THREAD,
      wxThreadEventHandler(MyDllApp::OnTerminate));
}

void MyDllApp::OnShowWindow(wxThreadEvent& event)
{
  puts("received show window command");
  wxFrame *f = new MyDllFrame(NULL, event.GetString());
  f->Show(true);
}

void MyDllApp::OnTerminate(wxThreadEvent& WXUNUSED(event))
{
  puts("received terminate command");
  ExitMainLoop();
}


// ----------------------------------------------------------------------------
// application startup
// ----------------------------------------------------------------------------

// we can't have WinMain() in a DLL and want to start the app ourselves
IMPLEMENT_APP_NO_MAIN(MyDllApp)

namespace
{

  // Critical section that guards everything related to wxWidgets "main" thread
  // startup or shutdown.
  wxCriticalSection gs_wxStartupCS;
  // Handle of wx "main" thread if running, NULL otherwise
  bool mainThreadStarted = false;
  bool wxInitialized = false;
  pthread_t gs_wxMainThread;
  pthread_mutex_t hMutex;
  pthread_cond_t hEvent;


  //  wx application startup code -- runs from its own thread
  void* MyAppLauncher(void* event)
  {
    // Note: The thread that called run_wx_gui_from_dll() holds gs_wxStartupCS
    //       at this point and won't release it until we signal it.

    // IMPLEMENT_WXWIN_MAIN does this as the first thing
    wxDISABLE_DEBUG_SUPPORT();

    // We do this before wxEntry() explicitly, even though wxEntry() would
    // do it too, so that we know when wx is initialized and can signal
    // run_wx_gui_from_dll() about it *before* starting the event loop.
    wxInitializer wxinit;
    if ( !wxinit.IsOk() )
      return 0; // failed to init wx

    // Signal run_wx_gui_from_dll() that it can continue

    pthread_mutex_lock(&hMutex);
    wxInitialized = true;
    pthread_cond_signal(&hEvent);
    pthread_mutex_unlock(&hMutex);

    // Run the app:
    puts("applauncher: calling wxEntry");
    int argc = 0;
    wxEntry(argc, (wxChar**)NULL);

    pthread_exit(NULL);
  }

} // anonymous namespace

// ----------------------------------------------------------------------------
// public DLL interface
// ----------------------------------------------------------------------------

extern "C"
{

  void run_wx_gui_from_dll(const char *title)
  {
    // In order to prevent conflicts with hosting app's event loop, we
    // launch wx app from the DLL in its own thread.
    //
    // We can't even use wxInitializer: it initializes wxModules and one of
    // the modules it handles is wxThread's private module that remembers
    // ID of the main thread. But we need to fool wxWidgets into thinking that
    // the thread we are about to create now is the main thread, not the one
    // from which this function is called.
    //
    // Note that we cannot use wxThread here, because the wx library wasn't
    // initialized yet. wxCriticalSection is safe to use, though.

    wxCriticalSectionLocker lock(gs_wxStartupCS);

    if ( !mainThreadStarted )
      {
        pthread_attr_t attr;

        pthread_mutex_init(&hMutex, NULL);
        pthread_cond_init(&hEvent, NULL);

        pthread_attr_init(&attr);
        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

        int err = pthread_create(&gs_wxMainThread, &attr, &MyAppLauncher, NULL);

        pthread_attr_destroy(&attr);

        if ( err )
      {
            pthread_mutex_destroy(&hMutex);
            pthread_cond_destroy(&hEvent);
            puts("run: failed to create gs_wxMainThread");
            return; //error
      }

        mainThreadStarted = true;

        pthread_mutex_lock(&hMutex);
        while (!wxInitialized) {
      puts("run: wait for wx to init");
      pthread_cond_wait(&hEvent, &hMutex);
        }
        pthread_mutex_unlock(&hMutex);

    pthread_cond_destroy(&hEvent);
      }

    // Send a message to wx thread to show a new frame:
    wxThreadEvent *event =
      new wxThreadEvent(wxEVT_THREAD, CMD_SHOW_WINDOW);
    event->SetString(title);
    wxQueueEvent(wxApp::GetInstance(), event);

    sleep(3);
  }

  void wx_dll_cleanup()
  {
    wxCriticalSectionLocker lock(gs_wxStartupCS);

    if ( !mainThreadStarted ) {
      puts("cleanup: main thread not started");
      return;
    }

    // If wx main thread is running, we need to stop it. To accomplish this,
    // send a message telling it to terminate the app.
    wxThreadEvent *event =
      new wxThreadEvent(wxEVT_THREAD, CMD_TERMINATE);
    wxQueueEvent(wxApp::GetInstance(), event);

    // We must then wait for the thread to actually terminate.
    puts("cleanup: waiting for main thread to finish");
    pthread_join(gs_wxMainThread, NULL);
    pthread_mutex_destroy(&hMutex);
  }

} // extern "C"