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>

1 files changed, 73 insertions, 6 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.