a first stab against the note caption ownership mess

This should not change any existing behavior, but may help tracking down
what happens where and when. The final goal is to let ScCaptionPtr also
handle deletion of caption objects once they're unreferenced and guard
against dangling pointers and double delete, and/or to manage transfer
of ownership to the drawing layer. Further improvement to the structure
could involve a head data element so that the duplicated (and unused
except in head) mnRefs field could be eliminated and the walk simplified
when removing an element from the list.

Change-Id: Ifbb2fb1d9dc4d2594a1eae2a8489270dd1fe0d0c
Reviewed-on: https://gerrit.libreoffice.org/34616
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins <ci@libreoffice.org>

6 files changed, 391 insertions, 99 deletions

diff --git a/sc/inc/postit.hxx b/sc/inc/postit.hxx
index 87553f3f5c3e..e8f212208289 100644
--- a/sc/inc/postit.hxx
+++ b/sc/inc/postit.hxx
@@ -36,6 +36,69 @@ class ScDocument;
 class Rectangle;
 struct ScCaptionInitData;
 
+/** Some desperate attempt to fight against the caption object ownership mess,
+    to which none of shared/weak/plain pointer is a cure.
+ */
+class ScCaptionPtr
+{
+public:
+    ScCaptionPtr();
+    explicit ScCaptionPtr( SdrCaptionObj* p );
+    ScCaptionPtr( const ScCaptionPtr& r );
+    ~ScCaptionPtr();
+
+    ScCaptionPtr& operator=( const ScCaptionPtr& r );
+    inline explicit operator bool() const    { return mpCaption != nullptr; }
+    inline SdrCaptionObj* get() const        { return mpCaption; }
+    inline SdrCaptionObj* operator->() const { return mpCaption; }
+    inline SdrCaptionObj& operator*() const  { return *mpCaption; }
+
+    // Does not default to nullptr to make it visually obvious where such is used.
+    void reset( SdrCaptionObj* p );
+
+    /** Release all management of the SdrCaptionObj* in all instances of this
+        list and dissolve. The SdrCaptionObj pointer returned is ready to be
+        managed elsewhere.
+     */
+    SdrCaptionObj* release();
+
+    /** Forget the SdrCaptionObj pointer in this one instance.
+        Decrements a use count but does not destroy the object, it's up to the
+        caller to manage this mess..
+        @returns <TRUE/> if the last reference was decremented.
+     */
+    bool forget();
+
+    oslInterlockedCount getRefs() const;
+
+private:
+    ScCaptionPtr*               mpHead;     ///< points to the "master" entry
+    mutable ScCaptionPtr*       mpNext;     ///< next in list
+    SdrCaptionObj*              mpCaption;  ///< the caption object, managed by head master
+    mutable oslInterlockedCount mnRefs;     ///< use count, managed by head master
+
+    void incRef() const;
+    bool decRef() const;        //< @returns <TRUE/> if the last reference was decremented.
+    void decRefAndDestroy();    //< Destroys caption object if the last reference was decremented.
+
+    /** Operations common to ctor and assignment operator, maintaining the lists. */
+    void assign( const ScCaptionPtr& r, bool bAssignment );
+
+    /** Remove from current list and close gap.
+
+        Usually there are only very few instances, so maintaining a doubly
+        linked list isn't worth memory/performance wise and a simple walk does
+        it.
+     */
+    void removeFromList();
+
+    /** Dissolve list when the caption object is released or gone. */
+    void dissolve();
+
+    /** Just clear everything, while dissolving the list. */
+    void clear();
+};
+
 /** Internal data for a cell annotation. */
 struct SC_DLLPUBLIC ScNoteData
 {
@@ -44,7 +107,7 @@ struct SC_DLLPUBLIC ScNoteData
     OUString     maDate;             /// Creation date of the note.
     OUString     maAuthor;           /// Author of the note.
     ScCaptionInitDataRef mxInitData;        /// Initial data for invisible notes without SdrObject.
-    SdrCaptionObj*      mpCaption;          /// Drawing object representing the cell note.
+    ScCaptionPtr        mxCaption;          /// Drawing object representing the cell note.
     bool                mbShown;            /// True = note is visible.
 
     explicit            ScNoteData( bool bShown = false );
@@ -124,10 +187,12 @@ public:
     void                SetText( const ScAddress& rPos, const OUString& rText );
 
     /** Returns an existing note caption object. returns null, if the note
-        contains initial caption data needed to construct a caption object. */
-    SdrCaptionObj* GetCaption() const { return maNoteData.mpCaption;}
+        contains initial caption data needed to construct a caption object.
+        The SdrCaptionObj* returned is unmanaged and must not be stored elsewhere. */
+    SdrCaptionObj*      GetCaption() const { return maNoteData.mxCaption.get();}
     /** Returns the caption object of this note. Creates the caption object, if
-        the note contains initial caption data instead of the caption. */
+        the note contains initial caption data instead of the caption.
+        The SdrCaptionObj* returned is unmanaged and must not be stored elsewhere. */
     SdrCaptionObj*      GetOrCreateCaption( const ScAddress& rPos ) const;
 
     /** Forgets the pointer to the note caption object.
@@ -179,8 +244,10 @@ public:
         This function is used in import filters to reuse the imported drawing
         object as note caption object.
 
-        @param rCaption  The drawing object for the cell note. This object MUST
+        @param pCaption  The drawing object for the cell note. This object MUST
             be inserted into the document at the correct drawing page already.
+            The underlying ScPostIt::ScNoteData::ScCaptionPtr takes managing
+            ownership of the pointer.
 
         @return  Pointer to the new cell note object if insertion was
             successful (i.e. the passed cell position was valid), null
@@ -190,7 +257,7 @@ public:
      */
     static ScPostIt*    CreateNoteFromCaption(
                             ScDocument& rDoc, const ScAddress& rPos,
-                            SdrCaptionObj& rCaption, bool bShown );
+                            SdrCaptionObj* pCaption, bool bShown );
 
     /** Creates a cell note based on the passed caption object data.
 
diff --git a/sc/source/core/data/postit.cxx b/sc/source/core/data/postit.cxx
index 83c6111823fa..baeca99d25b2 100644
--- a/sc/source/core/data/postit.cxx
+++ b/sc/source/core/data/postit.cxx
@@ -161,12 +161,12 @@ public:
     /** Create a new caption. The caption will not be inserted into the document. */
     explicit            ScCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, bool bTailFront );
     /** Manipulate an existing caption. */
-    explicit            ScCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, SdrCaptionObj& rCaption );
+    explicit            ScCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScCaptionPtr& xCaption );
 
     /** Returns the drawing layer page of the sheet contained in maPos. */
     SdrPage*            GetDrawPage();
     /** Returns the caption drawing object. */
-    inline SdrCaptionObj* GetCaption() { return mpCaption; }
+    inline ScCaptionPtr GetCaption() { return mxCaption; }
 
     /** Moves the caption inside the passed rectangle. Uses page area if 0 is passed. */
     void                FitCaptionToRect( const Rectangle* pVisRect = nullptr );
@@ -193,7 +193,7 @@ private:
 private:
     ScDocument&         mrDoc;
     ScAddress           maPos;
-    SdrCaptionObj*      mpCaption;
+    ScCaptionPtr        mxCaption;
     Rectangle           maPageRect;
     Rectangle           maCellRect;
     bool                mbNegPage;
@@ -201,25 +201,23 @@ private:
 
 ScCaptionCreator::ScCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, bool bTailFront ) :
     mrDoc( rDoc ),
-    maPos( rPos ),
-    mpCaption( nullptr )
+    maPos( rPos )
 {
     Initialize();
     CreateCaption( true/*bShown*/, bTailFront );
 }
 
-ScCaptionCreator::ScCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, SdrCaptionObj& rCaption ) :
+ScCaptionCreator::ScCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScCaptionPtr& xCaption ) :
     mrDoc( rDoc ),
     maPos( rPos ),
-    mpCaption( &rCaption )
+    mxCaption( xCaption )
 {
     Initialize();
 }
 
 ScCaptionCreator::ScCaptionCreator( ScDocument& rDoc, const ScAddress& rPos ) :
     mrDoc( rDoc ),
-    maPos( rPos ),
-    mpCaption( nullptr )
+    maPos( rPos )
 {
     Initialize();
 }
@@ -235,13 +233,13 @@ void ScCaptionCreator::FitCaptionToRect( const Rectangle* pVisRect )
     const Rectangle& rVisRect = GetVisRect( pVisRect );
 
     // tail position
-    Point aTailPos = mpCaption->GetTailPos();
+    Point aTailPos = mxCaption->GetTailPos();
     aTailPos.X() = ::std::max( ::std::min( aTailPos.X(), rVisRect.Right() ), rVisRect.Left() );
     aTailPos.Y() = ::std::max( ::std::min( aTailPos.Y(), rVisRect.Bottom() ), rVisRect.Top() );
-    mpCaption->SetTailPos( aTailPos );
+    mxCaption->SetTailPos( aTailPos );
 
     // caption rectangle
-    Rectangle aCaptRect = mpCaption->GetLogicRect();
+    Rectangle aCaptRect = mxCaption->GetLogicRect();
     Point aCaptPos = aCaptRect.TopLeft();
     // move textbox inside right border of visible area
     aCaptPos.X() = ::std::min< long >( aCaptPos.X(), rVisRect.Right() - aCaptRect.GetWidth() );
@@ -253,7 +251,7 @@ void ScCaptionCreator::FitCaptionToRect( const Rectangle* pVisRect )
     aCaptPos.Y() = ::std::max< long >( aCaptPos.Y(), rVisRect.Top() );
     // update caption
     aCaptRect.SetPos( aCaptPos );
-    mpCaption->SetLogicRect( aCaptRect );
+    mxCaption->SetLogicRect( aCaptRect );
 }
 
 void ScCaptionCreator::AutoPlaceCaption( const Rectangle* pVisRect )
@@ -261,7 +259,7 @@ void ScCaptionCreator::AutoPlaceCaption( const Rectangle* pVisRect )
     const Rectangle& rVisRect = GetVisRect( pVisRect );
 
     // caption rectangle
-    Rectangle aCaptRect = mpCaption->GetLogicRect();
+    Rectangle aCaptRect = mxCaption->GetLogicRect();
     long nWidth = aCaptRect.GetWidth();
     long nHeight = aCaptRect.GetHeight();
 
@@ -319,7 +317,7 @@ void ScCaptionCreator::AutoPlaceCaption( const Rectangle* pVisRect )
 
     // update textbox position in note caption object
     aCaptRect.SetPos( aCaptPos );
-    mpCaption->SetLogicRect( aCaptRect );
+    mxCaption->SetLogicRect( aCaptRect );
     FitCaptionToRect( pVisRect );
 }
 
@@ -328,33 +326,33 @@ void ScCaptionCreator::UpdateCaptionPos()
     ScDrawLayer* pDrawLayer = mrDoc.GetDrawLayer();
 
     // update caption position
-    const Point& rOldTailPos = mpCaption->GetTailPos();
+    const Point& rOldTailPos = mxCaption->GetTailPos();
     Point aTailPos = CalcTailPos( false );
     if( rOldTailPos != aTailPos )
     {
         // create drawing undo action
         if( pDrawLayer && pDrawLayer->IsRecording() )
-            pDrawLayer->AddCalcUndo( new SdrUndoGeoObj( *mpCaption ) );
+            pDrawLayer->AddCalcUndo( new SdrUndoGeoObj( *mxCaption ) );
         // calculate new caption rectangle (#i98141# handle LTR<->RTL switch correctly)
-        Rectangle aCaptRect = mpCaption->GetLogicRect();
+        Rectangle aCaptRect = mxCaption->GetLogicRect();
         long nDiffX = (rOldTailPos.X() >= 0) ? (aCaptRect.Left() - rOldTailPos.X()) : (rOldTailPos.X() - aCaptRect.Right());
         if( mbNegPage ) nDiffX = -nDiffX - aCaptRect.GetWidth();
         long nDiffY = aCaptRect.Top() - rOldTailPos.Y();
         aCaptRect.SetPos( aTailPos + Point( nDiffX, nDiffY ) );
         // set new tail position and caption rectangle
-        mpCaption->SetTailPos( aTailPos );
-        mpCaption->SetLogicRect( aCaptRect );
+        mxCaption->SetTailPos( aTailPos );
+        mxCaption->SetLogicRect( aCaptRect );
         // fit caption into draw page
         FitCaptionToRect();
     }
 
     // update cell position in caption user data
-    ScDrawObjData* pCaptData = ScDrawLayer::GetNoteCaptionData( mpCaption, maPos.Tab() );
+    ScDrawObjData* pCaptData = ScDrawLayer::GetNoteCaptionData( mxCaption.get(), maPos.Tab() );
     if( pCaptData && (maPos != pCaptData->maStart) )
     {
         // create drawing undo action
         if( pDrawLayer && pDrawLayer->IsRecording() )
-            pDrawLayer->AddCalcUndo( new ScUndoObjData( mpCaption, pCaptData->maStart, pCaptData->maEnd, maPos, pCaptData->maEnd ) );
+            pDrawLayer->AddCalcUndo( new ScUndoObjData( mxCaption.get(), pCaptData->maStart, pCaptData->maEnd, maPos, pCaptData->maEnd ) );
         // set new position
         pCaptData->maStart = maPos;
     }
@@ -376,9 +374,9 @@ void ScCaptionCreator::CreateCaption( bool bShown, bool bTailFront )
     // create the caption drawing object
     Rectangle aTextRect( Point( 0 , 0 ), Size( SC_NOTECAPTION_WIDTH, SC_NOTECAPTION_HEIGHT ) );
     Point aTailPos = CalcTailPos( bTailFront );
-    mpCaption = new SdrCaptionObj( aTextRect, aTailPos );
+    mxCaption.reset( new SdrCaptionObj( aTextRect, aTailPos ));
     // basic caption settings
-    ScCaptionUtil::SetBasicCaptionSettings( *mpCaption, bShown );
+    ScCaptionUtil::SetBasicCaptionSettings( *mxCaption, bShown );
 }
 
 void ScCaptionCreator::Initialize()
@@ -402,7 +400,7 @@ public:
     /** Create a new caption object and inserts it into the document. */
     explicit            ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScNoteData& rNoteData );
     /** Manipulate an existing caption. */
-    explicit            ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, SdrCaptionObj& rCaption, bool bShown );
+    explicit            ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScCaptionPtr& xCaption, bool bShown );
 };
 
 ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScNoteData& rNoteData ) :
@@ -414,37 +412,257 @@ ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& r
     {
         // create the caption drawing object
         CreateCaption( rNoteData.mbShown, false );
-        rNoteData.mpCaption = GetCaption();
-        OSL_ENSURE( rNoteData.mpCaption, "ScNoteCaptionCreator::ScNoteCaptionCreator - missing caption object" );
-        if( rNoteData.mpCaption )
+        rNoteData.mxCaption = GetCaption();
+        OSL_ENSURE( rNoteData.mxCaption, "ScNoteCaptionCreator::ScNoteCaptionCreator - missing caption object" );
+        if( rNoteData.mxCaption )
         {
             // store note position in user data of caption object
-            ScCaptionUtil::SetCaptionUserData( *rNoteData.mpCaption, rPos );
+            ScCaptionUtil::SetCaptionUserData( *rNoteData.mxCaption, rPos );
             // insert object into draw page
-            pDrawPage->InsertObject( rNoteData.mpCaption );
+            pDrawPage->InsertObject( rNoteData.mxCaption.get() );
         }
     }
 }
 
-ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, SdrCaptionObj& rCaption, bool bShown ) :
-    ScCaptionCreator( rDoc, rPos, rCaption )
+ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScCaptionPtr& xCaption, bool bShown ) :
+    ScCaptionCreator( rDoc, rPos, xCaption )
 {
     SdrPage* pDrawPage = GetDrawPage();
     OSL_ENSURE( pDrawPage, "ScNoteCaptionCreator::ScNoteCaptionCreator - no drawing page" );
-    OSL_ENSURE( rCaption.GetPage() == pDrawPage, "ScNoteCaptionCreator::ScNoteCaptionCreator - wrong drawing page in caption" );
-    if( pDrawPage && (rCaption.GetPage() == pDrawPage) )
+    OSL_ENSURE( xCaption->GetPage() == pDrawPage, "ScNoteCaptionCreator::ScNoteCaptionCreator - wrong drawing page in caption" );
+    if( pDrawPage && (xCaption->GetPage() == pDrawPage) )
     {
         // store note position in user data of caption object
-        ScCaptionUtil::SetCaptionUserData( rCaption, rPos );
+        ScCaptionUtil::SetCaptionUserData( *xCaption, rPos );
         // basic caption settings
-        ScCaptionUtil::SetBasicCaptionSettings( rCaption, bShown );
+        ScCaptionUtil::SetBasicCaptionSettings( *xCaption, bShown );
         // set correct tail position
-        rCaption.SetTailPos( CalcTailPos( false ) );
+        xCaption->SetTailPos( CalcTailPos( false ) );
     }
 }
 
 } // namespace
 
+
+ScCaptionPtr::ScCaptionPtr() :
+    mpHead(nullptr), mpNext(nullptr), mpCaption(nullptr), mnRefs(0)
+{
+}
+
+ScCaptionPtr::ScCaptionPtr( SdrCaptionObj* p ) :
+    mpHead( p ? this : nullptr ), mpNext(nullptr), mpCaption(p), mnRefs( p ? 1 : 0 )
+{
+}
+
+ScCaptionPtr::ScCaptionPtr( const ScCaptionPtr& r ) :
+    mpHead(nullptr), mpNext(nullptr), mpCaption(nullptr), mnRefs(0)
+{
+    assign( r, false);
+}
+
+void ScCaptionPtr::assign( const ScCaptionPtr& r, bool bAssignment )
+{
+    if (mpCaption == r.mpCaption)
+        return;
+
+    // Let's find some weird usage.
+    // Though assigning some other of the same list to head may syntactically
+    // be valid, why would we do that?
+    assert(r.mpHead != this);
+    // Same for assigning head to some other.
+    assert(mpHead != &r);
+    // And any other of the same list.
+    assert(mpHead != r.mpHead);
+
+    r.incRef();
+    if (bAssignment)
+    {
+        decRefAndDestroy();
+        removeFromList();
+    }
+    mpCaption = r.mpCaption;
+    // That head is this' master.
+    mpHead = r.mpHead;
+    mnRefs = 0;
+    // Insert into list.
+    mpNext = r.mpNext;
+    r.mpNext = this;
+}
+
+void ScCaptionPtr::removeFromList()
+{
+    if (!mpHead && !mpNext && !mpCaption && !mnRefs)
+        return;
+
+    ScCaptionPtr* pNewHead = (mpHead == this ? mpNext : nullptr);
+    ScCaptionPtr* pThat = (mpHead == this ? mpNext : mpHead);   // do not replace on self if head
+    while (pThat && pThat->mpNext != this)
+    {
+        // Use the walk to check consistency on the fly.
+        assert(pThat->mpCaption == nullptr || pThat->mpCaption == mpCaption);
+        assert(pThat->mnRefs == 0 || pThat == mpHead);
+        if (pNewHead)
+        {
+            assert(pThat->mpHead == mpHead);
+            pThat->mpHead = pNewHead;
+        }
+        pThat = pThat->mpNext;
+    }
+    assert(pThat || mpHead == this);  // not found only if this was head
+    if (pThat)
+    {
+        pThat->mpNext = mpNext;
+        if (pNewHead)
+        {
+            do
+            {
+                assert(pThat->mpCaption == nullptr || pThat->mpCaption == mpCaption);
+                assert(pThat->mnRefs == 0 || pThat == mpHead);
+                assert(pThat->mpHead == mpHead);
+                pThat->mpHead = pNewHead;
+            }
+            while ((pThat = pThat->mpNext) != nullptr);
+        }
+        else
+        {
+#if OSL_DEBUG_LEVEL > 0
+            // XXX exactly as for the if() branch but without replacing head.
+            do
+            {
+                assert(pThat->mpCaption == nullptr || pThat->mpCaption == mpCaption);
+                assert(pThat->mnRefs == 0 || pThat == mpHead);
+                assert(pThat->mpHead == mpHead);
+            }
+            while ((pThat = pThat->mpNext) != nullptr);
+#endif
+        }
+    }
+    if (pNewHead)
+        pNewHead->mnRefs = mnRefs;
+    mpHead = nullptr;
+    mpNext = nullptr;
+}
+
+void ScCaptionPtr::reset( SdrCaptionObj* p )
+{
+    assert(!p || p != mpCaption);
+#if OSL_DEBUG_LEVEL > 0
+    if (p)
+    {
+        // Check if we end up with a duplicated management in this list.
+        ScCaptionPtr* pThat = mpHead;
+        while (pThat)
+        {
+            assert(pThat->mpCaption != p);
+            pThat = pThat->mpNext;
+        }
+    }
+#endif
+    decRefAndDestroy();
+    removeFromList();
+    mpCaption = p;
+    if (p)
+    {
+        mpHead = this;
+        mnRefs = 1;
+    }
+    else
+    {
+        mpHead = nullptr;
+        mnRefs = 0;
+    }
+}
+
+ScCaptionPtr::~ScCaptionPtr()
+{
+    decRefAndDestroy();
+    removeFromList();
+}
+
+oslInterlockedCount ScCaptionPtr::getRefs() const
+{
+    assert(!mnRefs || mpHead == this);
+    return mpHead ? mpHead->mnRefs : mnRefs;
+}
+
+void ScCaptionPtr::incRef() const
+{
+    if (mpHead)
+        osl_atomic_increment(&mpHead->mnRefs);
+}
+
+bool ScCaptionPtr::decRef() const
+{
+    return mpHead && mpHead->mnRefs > 0 && !osl_atomic_decrement(&mpHead->mnRefs);
+}
+
+void ScCaptionPtr::decRefAndDestroy()
+{
+    if (decRef())
+    {
+        /* FIXME: this should eventually remove the caption from drawing layer
+         * foo and call SdrObject::Free(), likely with mpHead->mpCaption, see
+         * ScPostIt::RemoveCaption(). Further work needed to be able to do so.
+         * */
+        ScCaptionPtr* pThat = mpHead;
+        do
+        {
+            pThat->mpCaption = nullptr;
+            assert(pThat->mnRefs == 0);
+            pThat->mnRefs = 0;
+            pThat = pThat->mpNext;
+        }
+        while (pThat);
+        assert(!mpCaption); // this ought to be in list and nulled
+    }
+}
+
+SdrCaptionObj* ScCaptionPtr::release()
+{
+    SdrCaptionObj* pTmp = mpCaption;
+    dissolve();
+    return pTmp;
+}
+
+bool ScCaptionPtr::forget()
+{
+    bool bRet = decRef();
+    removeFromList();
+    mpCaption = nullptr;
+    mnRefs = 0;
+    return bRet;
+}
+
+void ScCaptionPtr::dissolve()
+{
+    ScCaptionPtr* pThat = mpHead;
+    while (pThat)
+    {
+        ScCaptionPtr* p = pThat->mpNext;
+        pThat->clear();
+        pThat = p;
+    }
+    clear();
+}
+
+void ScCaptionPtr::clear()
+{
+    mpHead = nullptr;
+    mpNext = nullptr;
+    mpCaption = nullptr;
+    mnRefs = 0;
+}
+
+ScCaptionPtr& ScCaptionPtr::operator=( const ScCaptionPtr& r )
+{
+    if (this == &r)
+        return *this;
+
+    assign( r, true);
+    return *this;
+}
+
+
 struct ScCaptionInitData
 {
     typedef ::std::unique_ptr< SfxItemSet >           SfxItemSetPtr;
@@ -466,7 +684,6 @@ ScCaptionInitData::ScCaptionInitData() :
 }
 
 ScNoteData::ScNoteData( bool bShown ) :
-    mpCaption( nullptr ),
     mbShown( bShown )
 {
 }
@@ -487,8 +704,8 @@ ScPostIt::ScPostIt( ScDocument& rDoc, const ScAddress& rPos, const ScPostIt& rNo
     mrDoc( rDoc ),
     maNoteData( rNote.maNoteData )
 {
-    maNoteData.mpCaption = nullptr;
-    CreateCaption( rPos, rNote.maNoteData.mpCaption );
+    maNoteData.mxCaption.reset(nullptr);
+    CreateCaption( rPos, rNote.maNoteData.mxCaption.get() );
 }
 
 ScPostIt::ScPostIt( ScDocument& rDoc, const ScAddress& rPos, const ScNoteData& rNoteData, bool bAlwaysCreateCaption ) :
@@ -528,8 +745,8 @@ void ScPostIt::AutoStamp()
 
 const OutlinerParaObject* ScPostIt::GetOutlinerObject() const
 {
-    if( maNoteData.mpCaption )
-        return maNoteData.mpCaption->GetOutlinerParaObject();
+    if( maNoteData.mxCaption )
+        return maNoteData.mxCaption->GetOutlinerParaObject();
     if( maNoteData.mxInitData.get() )
         return maNoteData.mxInitData->mxOutlinerObj.get();
     return nullptr;
@@ -574,14 +791,14 @@ bool ScPostIt::HasMultiLineText() const
 void ScPostIt::SetText( const ScAddress& rPos, const OUString& rText )
 {
     CreateCaptionFromInitData( rPos );
-    if( maNoteData.mpCaption )
-        maNoteData.mpCaption->SetText( rText );
+    if( maNoteData.mxCaption )
+        maNoteData.mxCaption->SetText( rText );
 }
 
 SdrCaptionObj* ScPostIt::GetOrCreateCaption( const ScAddress& rPos ) const
 {
     CreateCaptionFromInitData( rPos );
-    return maNoteData.mpCaption;
+    return maNoteData.mxCaption.get();
 }
 
 void ScPostIt::ForgetCaption( bool bPreserveData )
@@ -601,13 +818,13 @@ void ScPostIt::ForgetCaption( bool bPreserveData )
         pInitData->maSimpleText = GetText();
 
         maNoteData.mxInitData.reset(pInitData);
-        maNoteData.mpCaption = nullptr;
+        maNoteData.mxCaption.forget();
     }
     else
     {
         /*  This function is used in undo actions to give up the responsibility for
             the caption object which is handled by separate drawing undo actions. */
-        maNoteData.mpCaption = nullptr;
+        maNoteData.mxCaption.forget();
         maNoteData.mxInitData.reset();
     }
 }
@@ -617,23 +834,23 @@ void ScPostIt::ShowCaption( const ScAddress& rPos, bool bShow )
     CreateCaptionFromInitData( rPos );
     // no separate drawing undo needed, handled completely inside ScUndoShowHideNote
     maNoteData.mbShown = bShow;
-    if( maNoteData.mpCaption )
-        ScCaptionUtil::SetCaptionLayer( *maNoteData.mpCaption, bShow );
+    if( maNoteData.mxCaption )
+        ScCaptionUtil::SetCaptionLayer( *maNoteData.mxCaption, bShow );
 }
 
 void ScPostIt::ShowCaptionTemp( const ScAddress& rPos, bool bShow )
 {
     CreateCaptionFromInitData( rPos );
-    if( maNoteData.mpCaption )
-        ScCaptionUtil::SetCaptionLayer( *maNoteData.mpCaption, maNoteData.mbShown || bShow );
+    if( maNoteData.mxCaption )
+        ScCaptionUtil::SetCaptionLayer( *maNoteData.mxCaption, maNoteData.mbShown || bShow );
 }
 
 void ScPostIt::UpdateCaptionPos( const ScAddress& rPos )
 {
     CreateCaptionFromInitData( rPos );
-    if( maNoteData.mpCaption )
+    if( maNoteData.mxCaption )
     {
-        ScCaptionCreator aCreator( mrDoc, rPos, *maNoteData.mpCaption );
+        ScCaptionCreator aCreator( mrDoc, rPos, maNoteData.mxCaption );
         aCreator.UpdateCaptionPos();
     }
 }
@@ -642,7 +859,7 @@ void ScPostIt::UpdateCaptionPos( const ScAddress& rPos )
 
 void ScPostIt::CreateCaptionFromInitData( const ScAddress& rPos ) const
 {
-    OSL_ENSURE( maNoteData.mpCaption || maNoteData.mxInitData.get(), "ScPostIt::CreateCaptionFromInitData - need caption object or initial caption data" );
+    OSL_ENSURE( maNoteData.mxCaption || maNoteData.mxInitData.get(), "ScPostIt::CreateCaptionFromInitData - need caption object or initial caption data" );
     if( maNoteData.mxInitData.get() )
     {
         /*  This function is called from ScPostIt::Clone() when copying cells
@@ -652,22 +869,22 @@ void ScPostIt::CreateCaptionFromInitData( const ScAddress& rPos ) const
             been created already. Hovever, for clipboard in case the
             originating document was destructed a new caption has to be
             created. */
-        OSL_ENSURE( !mrDoc.IsUndo() && (!mrDoc.IsClipboard() || !maNoteData.mpCaption),
+        OSL_ENSURE( !mrDoc.IsUndo() && (!mrDoc.IsClipboard() || !maNoteData.mxCaption),
                 "ScPostIt::CreateCaptionFromInitData - note caption should not be created in undo/clip documents" );
 
         /*  #i104915# Never try to create notes in Undo document, leads to
             crash due to missing document members (e.g. row height array). */
-        if( !maNoteData.mpCaption && !mrDoc.IsUndo() )
+        if( !maNoteData.mxCaption && !mrDoc.IsUndo() )
         {
             if (mrDoc.IsClipboard())
                 mrDoc.InitDrawLayer();  // ensure there is a drawing layer
 
             // ScNoteCaptionCreator c'tor creates the caption and inserts it into the document and maNoteData
             ScNoteCaptionCreator aCreator( mrDoc, rPos, maNoteData );
-            if( maNoteData.mpCaption )
+            if( maNoteData.mxCaption )
             {
                 // Prevent triple change broadcasts of the same object.
-                SdrDelayBroadcastObjectChange aDelayChange( *maNoteData.mpCaption);
+                SdrDelayBroadcastObjectChange aDelayChange( *maNoteData.mxCaption);
 
                 ScCaptionInitData& rInitData = *maNoteData.mxInitData;
 
@@ -675,22 +892,22 @@ void ScPostIt::CreateCaptionFromInitData( const ScAddress& rPos ) const
                 OSL_ENSURE( rInitData.mxOutlinerObj.get() || !rInitData.maSimpleText.isEmpty(),
                     "ScPostIt::CreateCaptionFromInitData - need either outliner para object or simple text" );
                 if( rInitData.mxOutlinerObj.get() )
-                    maNoteData.mpCaption->SetOutlinerParaObject( rInitData.mxOutlinerObj.release() );
+                    maNoteData.mxCaption->SetOutlinerParaObject( rInitData.mxOutlinerObj.release() );
                 else
-                    maNoteData.mpCaption->SetText( rInitData.maSimpleText );
+                    maNoteData.mxCaption->SetText( rInitData.maSimpleText );
 
                 // copy all items or set default items; reset shadow items
-                ScCaptionUtil::SetDefaultItems( *maNoteData.mpCaption, mrDoc );
+                ScCaptionUtil::SetDefaultItems( *maNoteData.mxCaption, mrDoc );
                 if( rInitData.mxItemSet.get() )
-                    ScCaptionUtil::SetCaptionItems( *maNoteData.mpCaption, *rInitData.mxItemSet );
+                    ScCaptionUtil::SetCaptionItems( *maNoteData.mxCaption, *rInitData.mxItemSet );
 
                 // set position and size of the caption object
                 if( rInitData.mbDefaultPosSize )
                 {
                     // set other items and fit caption size to text
-                    maNoteData.mpCaption->SetMergedItem( makeSdrTextMinFrameWidthItem( SC_NOTECAPTION_WIDTH ) );
-                    maNoteData.mpCaption->SetMergedItem( makeSdrTextMaxFrameWidthItem( SC_NOTECAPTION_MAXWIDTH_TEMP ) );
-                    maNoteData.mpCaption->AdjustTextFrameWidthAndHeight();
+                    maNoteData.mxCaption->SetMergedItem( makeSdrTextMinFrameWidthItem( SC_NOTECAPTION_WIDTH ) );
+                    maNoteData.mxCaption->SetMergedItem( makeSdrTextMaxFrameWidthItem( SC_NOTECAPTION_MAXWIDTH_TEMP ) );
+                    maNoteData.mxCaption->AdjustTextFrameWidthAndHeight();
                     aCreator.AutoPlaceCaption();
                 }
                 else
@@ -700,7 +917,7 @@ void ScPostIt::CreateCaptionFromInitData( const ScAddress& rPos ) const
                     long nPosX = bNegPage ? (aCellRect.Left() - rInitData.maCaptionOffset.X()) : (aCellRect.Right() + rInitData.maCaptionOffset.X());
                     long nPosY = aCellRect.Top() + rInitData.maCaptionOffset.Y();
                     Rectangle aCaptRect( Point( nPosX, nPosY ), rInitData.maCaptionSize );
-                    maNoteData.mpCaption->SetLogicRect( aCaptRect );
+                    maNoteData.mxCaption->SetLogicRect( aCaptRect );
                     aCreator.FitCaptionToRect();
                 }
             }
@@ -712,8 +929,8 @@ void ScPostIt::CreateCaptionFromInitData( const ScAddress& rPos ) const
 
 void ScPostIt::CreateCaption( const ScAddress& rPos, const SdrCaptionObj* pCaption )
 {
-    OSL_ENSURE( !maNoteData.mpCaption, "ScPostIt::CreateCaption - unexpected caption object found" );
-    maNoteData.mpCaption = nullptr;
+    OSL_ENSURE( !maNoteData.mxCaption, "ScPostIt::CreateCaption - unexpected caption object found" );
+    maNoteData.mxCaption.reset(nullptr);
 
     /*  #i104915# Never try to create notes in Undo document, leads to
         crash due to missing document members (e.g. row height array). */
@@ -727,34 +944,34 @@ void ScPostIt::CreateCaption( const ScAddress& rPos, const SdrCaptionObj* pCapti
 
     // ScNoteCaptionCreator c'tor creates the caption and inserts it into the document and maNoteData
     ScNoteCaptionCreator aCreator( mrDoc, rPos, maNoteData );
-    if( maNoteData.mpCaption )
+    if( maNoteData.mxCaption )
     {
         // clone settings of passed caption
         if( pCaption )
         {
             // copy edit text object (object must be inserted into page already)
             if( OutlinerParaObject* pOPO = pCaption->GetOutlinerParaObject() )
-                maNoteData.mpCaption->SetOutlinerParaObject( new OutlinerParaObject( *pOPO ) );
+                maNoteData.mxCaption->SetOutlinerParaObject( new OutlinerParaObject( *pOPO ) );
             // copy formatting items (after text has been copied to apply font formatting)
-            maNoteData.mpCaption->SetMergedItemSetAndBroadcast( pCaption->GetMergedItemSet() );
+            maNoteData.mxCaption->SetMergedItemSetAndBroadcast( pCaption->GetMergedItemSet() );
             // move textbox position relative to new cell, copy textbox size
             Rectangle aCaptRect = pCaption->GetLogicRect();
-            Point aDist = maNoteData.mpCaption->GetTailPos() - pCaption->GetTailPos();
+            Point aDist = maNoteData.mxCaption->GetTailPos() - pCaption->GetTailPos();
             aCaptRect.Move( aDist.X(), aDist.Y() );
-            maNoteData.mpCaption->SetLogicRect( aCaptRect );
+            maNoteData.mxCaption->SetLogicRect( aCaptRect );
             aCreator.FitCaptionToRect();
         }
         else
         {
             // set default formatting and default position
-            ScCaptionUtil::SetDefaultItems( *maNoteData.mpCaption, mrDoc );
+            ScCaptionUtil::SetDefaultItems( *maNoteData.mxCaption, mrDoc );
             aCreator.AutoPlaceCaption();
         }
 
         // create undo action
         if( ScDrawLayer* pDrawLayer = mrDoc.GetDrawLayer() )
             if( pDrawLayer->IsRecording() )
-                pDrawLayer->AddCalcUndo( new SdrUndoNewObj( *maNoteData.mpCaption ) );
+                pDrawLayer->AddCalcUndo( new SdrUndoNewObj( *maNoteData.mxCaption ) );
     }
 }
 
@@ -765,10 +982,10 @@ void ScPostIt::RemoveCaption()
         undo documents refer to captions in original document, do not remove
         them from drawing layer here). */
     ScDrawLayer* pDrawLayer = mrDoc.GetDrawLayer();
-    if( maNoteData.mpCaption && (pDrawLayer == maNoteData.mpCaption->GetModel()) )
+    if( maNoteData.mxCaption && (pDrawLayer == maNoteData.mxCaption->GetModel()) )
     {
         OSL_ENSURE( pDrawLayer, "ScPostIt::RemoveCaption - object without drawing layer" );
-        SdrPage* pDrawPage = maNoteData.mpCaption->GetPage();
+        SdrPage* pDrawPage = maNoteData.mxCaption->GetPage();
         OSL_ENSURE( pDrawPage, "ScPostIt::RemoveCaption - object without drawing page" );
         if( pDrawPage )
         {
@@ -776,14 +993,20 @@ void ScPostIt::RemoveCaption()
             // create drawing undo action (before removing the object to have valid draw page in undo action)
             const bool bRecording = (pDrawLayer && pDrawLayer->IsRecording());
             if( bRecording )
-                pDrawLayer->AddCalcUndo( new SdrUndoDelObj( *maNoteData.mpCaption ) );
+                pDrawLayer->AddCalcUndo( new SdrUndoDelObj( *maNoteData.mxCaption.get() ) );
             // remove the object from the drawing page, delete if undo is disabled
-            SdrObject* pObj = pDrawPage->RemoveObject( maNoteData.mpCaption->GetOrdNum() );
+            SdrObject* pObj = pDrawPage->RemoveObject( maNoteData.mxCaption->GetOrdNum() );
             if( !bRecording )
+            {
+                maNoteData.mxCaption.release();
                 SdrObject::Free( pObj );
+            }
         }
     }
-    maNoteData.mpCaption = nullptr;
+    // Either the caption object is gone or, because of Undo or clipboard is
+    // held in at least two instances.
+    assert(!maNoteData.mxCaption || maNoteData.mxCaption.getRefs() >= 2);
+    maNoteData.mxCaption.reset(nullptr);
 }
 
 SdrCaptionObj* ScNoteUtil::CreateTempCaption(
@@ -814,7 +1037,9 @@ SdrCaptionObj* ScNoteUtil::CreateTempCaption(
 
     // create the caption object
     ScCaptionCreator aCreator( rDoc, rPos, bTailFront );
-    SdrCaptionObj* pCaption = aCreator.GetCaption();
+    // The caption object returned is completely unmanaged and stored
+    // elsewhere.
+    SdrCaptionObj* pCaption = aCreator.GetCaption().release();
 
     // insert caption into page (needed to set caption text)
     rDrawPage.InsertObject( pCaption );
@@ -849,17 +1074,17 @@ SdrCaptionObj* ScNoteUtil::CreateTempCaption(
 }
 
 ScPostIt* ScNoteUtil::CreateNoteFromCaption(
-        ScDocument& rDoc, const ScAddress& rPos, SdrCaptionObj& rCaption, bool bShown )
+        ScDocument& rDoc, const ScAddress& rPos, SdrCaptionObj* pCaption, bool bShown )
 {
     ScNoteData aNoteData( bShown );
-    aNoteData.mpCaption = &rCaption;
+    aNoteData.mxCaption.reset( pCaption );
     ScPostIt* pNote = new ScPostIt( rDoc, rPos, aNoteData, false );
     pNote->AutoStamp();
 
     rDoc.SetNote(rPos, pNote);
 
     // ScNoteCaptionCreator c'tor updates the caption object to be part of a note
-    ScNoteCaptionCreator aCreator( rDoc, rPos, rCaption, bShown );
+    ScNoteCaptionCreator aCreator( rDoc, rPos, aNoteData.mxCaption, bShown );
 
     return pNote;
 }
diff --git a/sc/source/filter/xml/xmlcelli.cxx b/sc/source/filter/xml/xmlcelli.cxx
index 8fd7edae9d15..3f894d112a3b 100644
--- a/sc/source/filter/xml/xmlcelli.cxx
+++ b/sc/source/filter/xml/xmlcelli.cxx
@@ -865,7 +865,7 @@ void ScXMLTableRowCellContext::SetAnnotation(const ScAddress& rPos)
             {
                 OSL_ENSURE( !pCaption->GetLogicRect().IsEmpty(), "ScXMLTableRowCellContext::SetAnnotation - invalid caption rectangle" );
                 // create the cell note with the caption object
-                pNote = ScNoteUtil::CreateNoteFromCaption( *pDoc, rPos, *pCaption, true );
+                pNote = ScNoteUtil::CreateNoteFromCaption( *pDoc, rPos, pCaption, true );
                 // forget pointer to object (do not create note again below)
                 pObject = nullptr;
             }
diff --git a/sc/source/ui/docshell/docfunc.cxx b/sc/source/ui/docshell/docfunc.cxx
index f6ce56e90219..d4d7e0ccbbdd 100644
--- a/sc/source/ui/docshell/docfunc.cxx
+++ b/sc/source/ui/docshell/docfunc.cxx
@@ -1298,7 +1298,7 @@ void ScDocFunc::ReplaceNote( const ScAddress& rPos, const OUString& rNoteText, c
         }
 
         // create the undo action
-        if( pUndoMgr && (aOldData.mpCaption || aNewData.mpCaption) )
+        if( pUndoMgr && (aOldData.mxCaption || aNewData.mxCaption) )
             pUndoMgr->AddUndoAction( new ScUndoReplaceNote( rDocShell, rPos, aOldData, aNewData, pDrawLayer->GetCalcUndo() ) );
 
         // repaint cell (to make note marker visible)
diff --git a/sc/source/ui/undo/undocell.cxx b/sc/source/ui/undo/undocell.cxx
index 0656483b60bd..ee8ec67237c2 100644
--- a/sc/source/ui/undo/undocell.cxx
+++ b/sc/source/ui/undo/undocell.cxx
@@ -708,7 +708,7 @@ ScUndoReplaceNote::ScUndoReplaceNote( ScDocShell& rDocShell, const ScAddress& rP
     maPos( rPos ),
     mpDrawUndo( pDrawUndo )
 {
-    OSL_ENSURE( rNoteData.mpCaption, "ScUndoReplaceNote::ScUndoReplaceNote - missing note caption" );
+    OSL_ENSURE( rNoteData.mxCaption, "ScUndoReplaceNote::ScUndoReplaceNote - missing note caption" );
     (bInsert ? maNewData : maOldData) = rNoteData;
 }
 
@@ -720,7 +720,7 @@ ScUndoReplaceNote::ScUndoReplaceNote( ScDocShell& rDocShell, const ScAddress& rP
     maNewData( rNewData ),
     mpDrawUndo( pDrawUndo )
 {
-    OSL_ENSURE( maOldData.mpCaption || maNewData.mpCaption, "ScUndoReplaceNote::ScUndoReplaceNote - missing note captions" );
+    OSL_ENSURE( maOldData.mxCaption || maNewData.mxCaption, "ScUndoReplaceNote::ScUndoReplaceNote - missing note captions" );
     OSL_ENSURE( !maOldData.mxInitData.get() && !maNewData.mxInitData.get(), "ScUndoReplaceNote::ScUndoReplaceNote - unexpected unitialized note" );
 }
 
@@ -766,13 +766,13 @@ bool ScUndoReplaceNote::CanRepeat( SfxRepeatTarget& /*rTarget*/ ) const
 
 OUString ScUndoReplaceNote::GetComment() const
 {
-    return ScGlobal::GetRscString( maNewData.mpCaption ?
-        (maOldData.mpCaption ? STR_UNDO_EDITNOTE : STR_UNDO_INSERTNOTE) : STR_UNDO_DELETENOTE );
+    return ScGlobal::GetRscString( maNewData.mxCaption ?
+        (maOldData.mxCaption ? STR_UNDO_EDITNOTE : STR_UNDO_INSERTNOTE) : STR_UNDO_DELETENOTE );
 }
 
 void ScUndoReplaceNote::DoInsertNote( const ScNoteData& rNoteData )
 {
-    if( rNoteData.mpCaption )
+    if( rNoteData.mxCaption )
     {
         ScDocument& rDoc = pDocShell->GetDocument();
         OSL_ENSURE( !rDoc.GetNote(maPos), "ScUndoReplaceNote::DoInsertNote - unexpected cell note" );
@@ -784,7 +784,7 @@ void ScUndoReplaceNote::DoInsertNote( const ScNoteData& rNoteData )
 
 void ScUndoReplaceNote::DoRemoveNote( const ScNoteData& rNoteData )
 {
-    if( rNoteData.mpCaption )
+    if( rNoteData.mxCaption )
     {
         ScDocument& rDoc = pDocShell->GetDocument();
         OSL_ENSURE( rDoc.GetNote(maPos), "ScUndoReplaceNote::DoRemoveNote - missing cell note" );
diff --git a/sc/source/ui/view/drawview.cxx b/sc/source/ui/view/drawview.cxx
index 03e5746995d9..ab4315495101 100644
--- a/sc/source/ui/view/drawview.cxx
+++ b/sc/source/ui/view/drawview.cxx
@@ -869,7 +869,7 @@ void ScDrawView::DeleteMarked()
         {
             // rescue note data for undo (with pointer to caption object)
             ScNoteData aNoteData = pNote->GetNoteData();
-            OSL_ENSURE( aNoteData.mpCaption == pCaptObj, "ScDrawView::DeleteMarked - caption object does not match" );
+            OSL_ENSURE( aNoteData.mxCaption.get() == pCaptObj, "ScDrawView::DeleteMarked - caption object does not match" );
             // collect the drawing undo action created while deleting the note
             if( bUndo )
                 pDrawLayer->BeginCalcUndo(false);