Make main thread wake up code more efficient and less error-prone in wxMSW.

Use a kernel event object to signal the thread wake up instead of sending
WM_NULL to one of its windows. This is simpler as we don't need to look for
any windows and doesn't suffer from the problem of overflowing the Windows
message queue if we do it too many times as signalling an already signalled
event simply doesn't do anything.

Closes #9053.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78041 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/evtloop.h

@@ -53,7 +53,6 @@ public:
     // override/implement base class virtuals
     virtual bool Dispatch();
     virtual int DispatchTimeout(unsigned long timeout);
-    virtual void WakeUp();
 
 protected:
     virtual void OnNextIteration();

include/wx/msw/evtloopconsole.h

@@ -15,9 +15,20 @@ class WXDLLIMPEXP_BASE wxMSWEventLoopBase : public wxEventLoopManual
 {
 public:
     wxMSWEventLoopBase();
+    virtual ~wxMSWEventLoopBase();
 
     // implement base class pure virtuals
     virtual bool Pending() const;
+    virtual void WakeUp();
+
+#if wxUSE_THREADS
+    // MSW-specific method to wait for the termination of the specified (by its
+    // native handle) thread or any input message arriving (in GUI case).
+    //
+    // Return value is WAIT_OBJECT_0 if the thread terminated, WAIT_OBJECT_0+1
+    // if a message arrived with anything else indicating an error.
+    WXDWORD MSWWaitForThread(WXHANDLE hThread);
+#endif // wxUSE_THREADS
 
 protected:
     // get the next message from queue and return true or return false if we
@@ -25,8 +36,13 @@ protected:
     bool GetNextMessage(WXMSG *msg);
 
     // same as above but with a timeout and return value can be -1 meaning that
-    // time out expired in addition to
+    // time out expired in addition to true/false
     int GetNextMessageTimeout(WXMSG *msg, unsigned long timeout);
+
+private:
+    // An auto-reset Win32 event which is signalled when we need to wake up the
+    // main thread waiting in GetNextMessage[Timeout]().
+    WXHANDLE m_heventWake;
 };
 
 #if wxUSE_CONSOLE_EVENTLOOP
@@ -39,7 +55,6 @@ public:
     // override/implement base class virtuals
     virtual bool Dispatch();
     virtual int DispatchTimeout(unsigned long timeout);
-    virtual void WakeUp();
 
     // Windows-specific function to process a single message
     virtual void ProcessMessage(WXMSG *msg);

src/msw/app.cpp

@@ -232,23 +232,16 @@ WXDWORD wxGUIAppTraits::WaitForThread(WXHANDLE hThread, int flags)
     // have a running event loop as we would never remove them from the message
     // queue then and so we would enter an infinite loop as
     // MsgWaitForMultipleObjects() keeps returning WAIT_OBJECT_0 + 1.
-    if ( flags == wxTHREAD_WAIT_BLOCK ||
+    if ( flags == wxTHREAD_WAIT_YIELD && wxIsMainThread() )
-            !wxIsMainThread() ||
-                !wxEventLoop::GetActive() )
     {
-        // Simple blocking wait.
+        wxMSWEventLoopBase* const
-        return DoSimpleWaitForThread(hThread);
+            evtLoop = static_cast<wxMSWEventLoopBase *>(wxEventLoop::GetActive());
+        if ( evtLoop )
+            return evtLoop->MSWWaitForThread(hThread);
     }
 
-    return ::MsgWaitForMultipleObjects
+    // Simple blocking wait.
-             (
+    return DoSimpleWaitForThread(hThread);
-               1,                   // number of objects to wait for
-               (HANDLE *)&hThread,  // the objects
-               false,               // wait for any objects, not all
-               INFINITE,            // no timeout
-               QS_ALLINPUT |        // return as soon as there are any events
-               QS_ALLPOSTMESSAGE
-             );
 }
 #endif // wxUSE_THREADS
 
@@ -780,42 +773,16 @@ void wxApp::OnIdle(wxIdleEvent& WXUNUSED(event))
 
 void wxApp::WakeUpIdle()
 {
-    // Send the top window a dummy message so idle handler processing will
+    wxEventLoopBase * const evtLoop = wxEventLoop::GetActive();
-    // start up again.  Doing it this way ensures that the idle handler
+    if ( !evtLoop )
-    // wakes up in the right thread (see also wxWakeUpMainThread() which does
-    // the same for the main app thread only)
-    wxWindow * const topWindow = wxTheApp->GetTopWindow();
-    if ( topWindow )
     {
-        HWND hwndTop = GetHwndOf(topWindow);
+        // We can't wake up the event loop if there is none and there is just
-
+        // no need to do anything in this case, any pending events will be
-        // Do not post WM_NULL if there's already a pending WM_NULL to avoid
+        // handled when the event loop starts.
-        // overflowing the message queue.
+        return;
-        //
-        // Notice that due to a limitation of PeekMessage() API (which handles
-        // 0,0 range specially), we have to check the range from 0-1 instead.
-        // This still makes it possible to overflow the queue with WM_NULLs by
-        // interspersing the calles to WakeUpIdle() with windows creation but
-        // it should be rather hard to do it accidentally.
-        MSG msg;
-        if ( !::PeekMessage(&msg, hwndTop, 0, 1, PM_NOREMOVE) ||
-              ::PeekMessage(&msg, hwndTop, 1, 1, PM_NOREMOVE) )
-        {
-            // If this fails too, there is really not much we can do, but then
-            // neither do we need to, as it normally indicates that the window
-            // queue is full to the brim with the messages and so the main loop
-            // is running and doesn't need to be woken up.
-            //
-            // Notice that we especially should not try use wxLogLastError()
-            // here as this would lead to another call to wxWakeUpIdle() from
-            // inside wxLog and stack overflow due to the resulting recursion.
-            ::PostMessage(hwndTop, WM_NULL, 0, 0);
-        }
     }
-#if wxUSE_THREADS
+
-    else
+    evtLoop->WakeUp();
-        wxWakeUpMainThread();
-#endif // wxUSE_THREADS
 }
 
 // ----------------------------------------------------------------------------

src/msw/evtloop.cpp

@@ -250,11 +250,6 @@ void wxGUIEventLoop::OnNextIteration()
 #endif // wxUSE_THREADS
 }
 
-void wxGUIEventLoop::WakeUp()
-{
-    ::PostMessage(NULL, WM_NULL, 0, 0);
-}
-
 
 // ----------------------------------------------------------------------------
 // Yield to incoming messages

src/msw/evtloopconsole.cpp

@@ -42,6 +42,17 @@ wxMSWEventLoopBase::wxMSWEventLoopBase()
 {
     m_shouldExit = false;
     m_exitcode = 0;
+
+    // Create initially not signalled auto-reset event object.
+    m_heventWake = ::CreateEvent(NULL, FALSE, FALSE, NULL);
+    if ( !m_heventWake )
+        wxLogLastError(wxS("CreateEvent(wake)"));
+}
+
+wxMSWEventLoopBase::~wxMSWEventLoopBase()
+{
+    if ( m_heventWake && !::CloseHandle(m_heventWake) )
+        wxLogLastError(wxS("CloseHandle(wake)"));
 }
 
 // ----------------------------------------------------------------------------
@@ -54,26 +65,36 @@ bool wxMSWEventLoopBase::Pending() const
     return ::PeekMessage(&msg, 0, 0, 0, PM_NOREMOVE) != 0;
 }
 
+void wxMSWEventLoopBase::WakeUp()
+{
+    if ( !::SetEvent(m_heventWake) )
+        wxLogLastError(wxS("SetEvent(wake)"));
+}
+
+#if wxUSE_THREADS
+
+WXDWORD wxMSWEventLoopBase::MSWWaitForThread(WXHANDLE hThread)
+{
+    // The order is important here, the code using this function assumes that
+    // WAIT_OBJECT_0 indicates the thread termination and anything else -- the
+    // availability of an input event. So the thread handle must come first.
+    HANDLE handles[2] = { hThread, m_heventWake };
+    return ::MsgWaitForMultipleObjects
+             (
+               WXSIZEOF(handles),   // number of objects to wait for
+               handles,             // the objects
+               false,               // wait for any objects, not all
+               INFINITE,            // no timeout
+               QS_ALLINPUT |        // return as soon as there are any events
+               QS_ALLPOSTMESSAGE
+             );
+}
+
+#endif // wxUSE_THREADS
+
 bool wxMSWEventLoopBase::GetNextMessage(WXMSG* msg)
 {
-    const BOOL rc = ::GetMessage(msg, NULL, 0, 0);
+    return GetNextMessageTimeout(msg, INFINITE) == TRUE;
-
-    if ( rc == 0 )
-    {
-        // got WM_QUIT
-        return false;
-    }
-
-    if ( rc == -1 )
-    {
-        // should never happen, but let's test for it nevertheless
-        wxLogLastError(wxT("GetMessage"));
-
-        // still break from the loop
-        return false;
-    }
-
-    return true;
 }
 
 int wxMSWEventLoopBase::GetNextMessageTimeout(WXMSG *msg, unsigned long timeout)
@@ -86,14 +107,12 @@ int wxMSWEventLoopBase::GetNextMessageTimeout(WXMSG *msg, unsigned long timeout)
     //     it is not available in very old Windows versions
     if ( !::PeekMessage(msg, 0, 0, 0, PM_REMOVE) )
     {
-        // we use this function just in order to not block longer than the
-        // given timeout, so we don't pass any handles to it at all
         DWORD rc = ::MsgWaitForMultipleObjects
                      (
-                        0, NULL,
+                        1, &m_heventWake,
                         FALSE,
                         timeout,
-                        QS_ALLINPUT
+                        QS_ALLINPUT | QS_ALLPOSTMESSAGE
                      );
 
         switch ( rc )
@@ -107,6 +126,15 @@ int wxMSWEventLoopBase::GetNextMessageTimeout(WXMSG *msg, unsigned long timeout)
                 return -1;
 
             case WAIT_OBJECT_0:
+                // We were woken up by a background thread, which means there
+                // is no actual input message available, but we should still
+                // return to the event loop, so pretend there was WM_NULL in
+                // the queue.
+                wxZeroMemory(*msg);
+                break;
+
+            case WAIT_OBJECT_0 + 1:
+                // Some message is supposed to be available.
                 if ( !::PeekMessage(msg, 0, 0, 0, PM_REMOVE) )
                 {
                     // somehow it may happen that MsgWaitForMultipleObjects()
@@ -127,13 +155,6 @@ int wxMSWEventLoopBase::GetNextMessageTimeout(WXMSG *msg, unsigned long timeout)
 
 #if wxUSE_CONSOLE_EVENTLOOP
 
-void wxConsoleEventLoop::WakeUp()
-{
-#if wxUSE_THREADS
-    wxWakeUpMainThread();
-#endif
-}
-
 void wxConsoleEventLoop::ProcessMessage(WXMSG *msg)
 {
     ::DispatchMessage(msg);