Ticket #3433: 3433-v2.patch

libs/libmythtv/osdtypeteletext.h

@@ -18 +18 @@
 class OSD;
 class OSDType;
 class OSDSurface;
+class OSDTypeTeletext;
 class TV;
 
 class TTColor
@@ -106 +107 @@
     int_to_page_t     pages;
 };
 
+class OSDUpdateLocker
+{
+  public:
+    OSDUpdateLocker(QMutex *lock, OSDTypeTeletext *parent);
+    ~OSDUpdateLocker(void);
+
+  private:
+    QMutex          *m_lock;
+    OSDTypeTeletext *m_parent;
+};
+
 class OSDTypeTeletext : public OSDType, public TeletextViewer
 {
     Q_OBJECT
+
     friend QColor color_tt2qt(int ttcolor);
+    friend class OSDUpdateLocker;
+
   public:
     OSDTypeTeletext(const QString &name, TTFFont *font,
                     QRect displayrect, float wmult, float hmult, OSD *osd);
@@ -209 +224 @@
     uint8_t      m_header[40];
     mutable bool m_header_changed;
     mutable bool m_page_changed;
+    mutable bool m_osd_changed;
 
     TeletextMagazine m_magazines[8];
     unsigned char    m_bitswap[256];

libs/libmythtv/osdtypeteletext.cpp

@@ -68 +68 @@
 
       m_transparent(false),             m_revealHidden(false),
       m_displaying(false),              m_osd(osd),
-      m_header_changed(false),          m_page_changed(false)
+      m_header_changed(false),          m_page_changed(false),
+      m_osd_changed(false)
 {
     m_unbiasedrect  = bias(m_displayrect, wmult, hmult);
 
@@ -89 +90 @@
  */
 void OSDTypeTeletext::Reset(void)
 {
-    QMutexLocker locker(&m_lock);
+    OSDUpdateLocker locker(&m_lock, this);
 
     for (uint mag = 0; mag < 8; mag++)
     {
@@ -129 +130 @@
                                     const unsigned char* buf,
                                     int vbimode, int lang, int flags)
 {
-    QMutexLocker locker(&m_lock);
+    OSDUpdateLocker locker(&m_lock, this);
 
     int magazine = MAGAZINE(page);
     if (magazine < 1 || magazine > 8)
@@ -207 +208 @@
 void OSDTypeTeletext::AddTeletextData(int magazine, int row, 
                                       const unsigned char* buf, int vbimode)
 {
-    QMutexLocker locker(&m_lock);
+    OSDUpdateLocker locker(&m_lock, this);
 
     int b1, b2, b3, err;
 
@@ -322 +323 @@
         return;
 
     m_page_changed = true;
-    m_osd->UpdateTeletext();
+    m_osd_changed = true;
+// note: We cannot call UpdateTeletext from here since it will try to get the
+//       osdlock. The problem with this is that the OSD::Display might already
+//       be active and have called our Draw function and hence is pending the
+//       m_lock being freed. Since the OSD::Display uses the osdlock, our call
+//       to the UpdateTeletext would result in a semaphore deadlock.
+//    m_osd->UpdateTeletext();
 }
 
 /** \fn OSDTypeTeletext::HeaderUpdated(unsigned char*,int)
@@ -479 +486 @@
  */
 void OSDTypeTeletext::KeyPress(uint key)
 {
-    QMutexLocker locker(&m_lock);
+    OSDUpdateLocker locker(&m_lock, this);
 
     int newPage = m_curpage;
     int newSubPage = m_cursubpage;
@@ -665 +672 @@
  */
 void OSDTypeTeletext::SetPage(int page, int subpage)
 {
-    QMutexLocker locker(&m_lock);
+    OSDUpdateLocker locker(&m_lock, this);
 
     if (page < 0x100 || page > 0x899)
         return;
@@ -1109 +1116 @@
 
 void OSDTypeTeletext::Reinit(float wmult, float hmult)
 {
-    QMutexLocker locker(&m_lock);
+    OSDUpdateLocker locker(&m_lock, this);
 
     m_displayrect = bias(m_unbiasedrect, wmult, hmult);
     m_tt_colspace = m_displayrect.width()  / kTeletextColumns;
@@ -1232 +1239 @@
     }
 }
 
+/**
+ * \class OSDUpdateLocker
+ * \brief Helper class to the OSDTypeTeletext
+ *
+ * This class is used to lock the m_lock semaphore when
+ * there is a chance that the locked code will result in the
+ * OSD::UpdateTeletext() function being called. It's purpose
+ * is to lock the semaphore and once the locked code has
+ * finished to check for a request to call OSD::UpdateTeletext().
+ * If required, the m_lock is released and the required call made
+ *
+ * This is to overcome the possible semaphore deadlock as follows:
+ * \code
+ *  - Teletext data arrives -> locks m_lock
+ *  - While the teletext data is being processed the XMV request an
+ *    OSD update display
+ *  - The OSD update display will lock the osdlock
+ *  - The OSD update can results in the Teletext:Draw method being
+ *    called and hence the OSD update is now waiting on m_lock being
+ *    released to continue it's drawing process
+ *  - If the processing of the teletext data result in the function
+ *    OSD::UpdateTeletext being called, this function will try to
+ *    get the osdlock.
+ *  - This results in the classic semaphore deadlock and hence all
+ *    OSD update cease.
+ * \endcode
+ **************************************************************************/
+
+OSDUpdateLocker::OSDUpdateLocker(QMutex *lock, OSDTypeTeletext *parent) :
+    m_lock(lock), m_parent(parent)
+{
+    m_lock->lock();
+}
+
+OSDUpdateLocker::~OSDUpdateLocker(void)
+{
+    // see if the osd has to be requested a redraw
+    if (m_parent->m_osd_changed)
+    {
+        m_parent->m_osd_changed = false;
+        m_lock->unlock();
+        // now it is safe to do the OSD update
+        m_parent->m_osd->UpdateTeletext();
+    }
+    else
+    {
+        // normal exit. Will result in the m_lock being released.
+        m_lock->unlock();
+    }
+}
+