Library: implement optional invocation of destructors

This is the first draft, implementing the invocation explicitly
through a trampoline function. While it seems to work,
the formulation can probably be simplified....

src/lib/allocation-cluster.cpp

@@ -70,8 +70,32 @@ namespace lib {
     {
       Alloc::destroy (heap, static_cast<std::byte *> (storage));
     }
+
+    /**
+     * Special allocator-policy for lib::LinkedElements
+     * - does not allow to allocate new elements
+     * - can hook up elements allocated elsewhere
+     * - ensure the destructor of all elements is invoked
+     */
+    struct PolicyInvokeDtor
+      : lib::linked_elements::NoOwnership
+      {
+        /**
+         * while this policy doesn't take ownership,
+         * it ensures the destructor is invoked
+         */
+        template<class X>
+        void
+        destroy (X* elm)
+          {
+            REQUIRE (elm);
+            elm->~X();
+          }
+      };
+
   }
   
+  
   /**
    * An _overlay view_ for the AllocationCluster to add functionality
    * for adding / clearing extents and registering optional deleter functions.
@@ -91,9 +115,15 @@ namespace lib {
       struct Destructor
         {
           Destructor* next;
-          ///////////////////////////////////////////////OOO store deleter function here
+          DtorInvoker dtor;
+          
+         ~Destructor()
+            {
+              if (dtor)
+                (*dtor) (this);
+            }
         };
-      using Destructors = lib::LinkedElements<Destructor>;
+      using Destructors = lib::LinkedElements<Destructor, PolicyInvokeDtor>;
       
       struct Extent
         : util::NonCopyable
@@ -112,7 +142,7 @@ namespace lib {
       
       ManagementView view_;
       
-      StorageManager()  = delete;    ///< @warning used as _overlay view_ only, never created 
+      StorageManager()  = delete;    ///< @warning used as _overlay view_ only, never created
       
     public:
       static StorageManager&
@@ -135,6 +165,20 @@ namespace lib {
           view_.extents.clear();
         }
       
+      void
+      addDestructor (void* dtor)
+        {
+          auto& destructor = * static_cast<Destructor*> (dtor);
+          getCurrentBlockStart()->dtors.push (destructor);
+        }
+      
+      void
+      discardLastDestructor()
+        {
+          getCurrentBlockStart()->dtors.pop();
+        }
+      
+      
       size_t
       determineExtentCnt() ///< @warning finalises current block
         {
@@ -152,12 +196,13 @@ namespace lib {
       static auto determineStorageSize (AllocationCluster const&);
       
     private:
-      byte*
+      Extent*
       getCurrentBlockStart()  const
         {
-          return static_cast<byte*>(view_.storage.pos)
+          void* pos = static_cast<byte*>(view_.storage.pos)
-                                  + view_.storage.rest
+                                       + view_.storage.rest
-                                  - EXTENT_SIZ;
+                                       - EXTENT_SIZ;
+          return static_cast<Extent*> (pos);
         }
       
       void
@@ -221,7 +266,22 @@ namespace lib {
     ENSURE (allocRequest + OVERHEAD <= EXTENT_SIZ);
     StorageManager::access(*this).addBlock();
   }
-
+  
+  
+  void
+  AllocationCluster::registerDestructor (void* dtor)
+  {
+    StorageManager::access(*this).addDestructor (dtor);
+  }
+  
+  
+  void
+  AllocationCluster::discardLastDestructor()
+  {
+    StorageManager::access(*this).discardLastDestructor();
+  }
+  
+  
   
   
   /* === diagnostics helpers === */

src/lib/allocation-cluster.hpp

@@ -45,6 +45,8 @@
 #include "lib/error.hpp"
 #include "lib/nocopy.hpp"
 
+#include <type_traits>
+#include <utility>
 #include <memory>
 
 
@@ -125,11 +127,10 @@ namespace lib {
       
       
       template<class TY, typename...ARGS>
-      TY&
+      TY& create (ARGS&& ...);
-      create (ARGS&& ...args)
+      
-        {
+      template<class TY, typename...ARGS>
-          return * new(allot<TY>()) TY (std::forward<ARGS> (args)...);
+      TY& createDisposable (ARGS&& ...);
-        }
       
       template<typename X>
       Allocator<X>
@@ -167,7 +168,14 @@ namespace lib {
           return static_cast<X*> (allotMemory (cnt * sizeof(X), alignof(X)));
         }
       
+      typedef void (*DtorInvoker) (void*);
+      
+      template<typename X>
+      void* allotWithDeleter();
+      
       void expandStorage (size_t);
+      void registerDestructor (void*);
+      void discardLastDestructor();
       bool _is_within_limits (size_t,size_t);
       
       friend class test::AllocationCluster_test;
@@ -179,6 +187,75 @@ namespace lib {
   
   //-----implementation-details------------------------
   
+  template<class TY, typename...ARGS>
+  TY&
+  AllocationCluster::createDisposable (ARGS&& ...args)
+  {
+    return * new(allot<TY>()) TY (std::forward<ARGS> (args)...);
+  }
+  
+  template<class TY, typename...ARGS>
+  TY&
+  AllocationCluster::create (ARGS&& ...args)
+  {
+    if constexpr (std::is_trivial_v<TY>)
+      return createDisposable<TY> (std::forward<ARGS> (args)...);
+    
+    void* storage = allotWithDeleter<TY>();
+    try {
+        return * new(storage) TY (std::forward<ARGS> (args)...);
+      }
+    catch(...)
+      {
+        discardLastDestructor();
+        throw;
+      }
+  }
+  
+  /**
+   * Establish a storage arrangement with a callback to invoke the destructor.
+   * @remark the purpose of AllocationCluster is to avoid deallocation of individual objects;
+   *         thus the position and type of allocated payload objects is discarded. However,
+   *         sometimes it is desirable to ensure invocation of object destructors; in this case,
+   *         a linked list of destructor callbacks is hooked up in the storage extent. These
+   *         callback records are always allocated directly before the actual payload object,
+   *         and use a special per-type trampoline function to invoke the destructor, passing
+   *         a properly adjusted self-pointer.
+   */
+  template<typename X>
+  void*
+  AllocationCluster::allotWithDeleter()
+  {
+    /**
+     * Memory layout frame to place a payload object
+     * and store a destructor callback as intrusive linked list.
+     * @note this object is never constructed, but it is used to
+     *       reinterpret the StorageManager::Destructor record,
+     *       causing invocation of the destructor of the payload object,
+     *       which is always placed immediately behind.
+     */
+    struct TypedDtorInvoker
+      {
+        void* next;
+        DtorInvoker dtor;
+        X payload;
+        
+        /** trampoline function: invoke the destructor of the payload type */
+        static void
+        invokePayloadDtor (void* self)
+          {
+            REQUIRE (self);
+            TypedDtorInvoker* instance = static_cast<TypedDtorInvoker*> (self);
+            instance->payload.~X();
+          }
+      };
+    
+    TypedDtorInvoker* allocation = allot<TypedDtorInvoker>();
+    allocation->dtor = &TypedDtorInvoker::invokePayloadDtor;
+    registerDestructor (allocation);
+    return & allocation->payload;
+  }
+  
   
 } // namespace lib
 #endif /*LIB_ALLOCATION_CLUSTER_H*/

src/lib/linked-elements.hpp

@@ -323,12 +323,20 @@ namespace lib {
         }
       
       
-//      template< class TY =N>
+      /** extract the top-most element, if any
-//      TY&                                                  //_________________________________________
+       * @warning gives up ownership; if this list manages ownership,
-//      emplace ()                                          ///< add object of type TY, using 0-arg ctor
+       *          then the caller is responsible for deallocating the removed entry
-//        {
+       * @return pointer to the removed element
-//          return push (ALO::template create<TY>());
+       */
-//        }
+      N*
+      pop()
+        {
+          N* elm = head_;
+          if (head_)
+            head_ = head_->next;
+          return elm;
+        }
+      
       
       /** prepend object of type TY, forwarding ctor args */
       template<class TY =N, typename...ARGS>

tests/library/allocation-cluster-test.cpp

@@ -201,6 +201,7 @@ namespace test {
       verifyInternals()
         {
           CHECK (0==checksum);
+          long markSum;
           {
             AllocationCluster clu;
             // no allocation happened yet
@@ -265,34 +266,17 @@ namespace test {
             CHECK (slot(0) == 0);
             
             // deliberately fill up the first extent completely
-SHOW_EXPR(size_t(currBlock()))
-SHOW_EXPR(size_t(clu.storage_.pos))
-SHOW_EXPR(clu.storage_.rest)
-SHOW_EXPR(posOffset())
             for (uint i=clu.storage_.rest; i>0; --i)
               clu.create<uchar> (i);
-SHOW_EXPR(size_t(currBlock()))
+            CHECK (clu.storage_.rest == 0);                            // no space left in current extent
-SHOW_EXPR(size_t(clu.storage_.pos))
-SHOW_EXPR(clu.storage_.rest)
-SHOW_EXPR(posOffset())
-SHOW_EXPR(slot(0))
-            CHECK (clu.storage_.rest == 0);
             CHECK (posOffset() == BLOCKSIZ);
-SHOW_EXPR(clu.numBytes())
+            CHECK (clu.numBytes() == BLOCKSIZ - 2*sizeof(void*));      // now using all the rest behind the admin »slots«
-            CHECK (clu.numBytes() == BLOCKSIZ - 2*sizeof(void*));
             CHECK (clu.numExtents() == 1);
             CHECK (slot(0) == 0);
             CHECK (blk == currBlock());                                // but still in the initial extent
             
             // trigger overflow and allocation of second extent
             char& c2 = clu.create<char> ('U');
-SHOW_EXPR(size_t(currBlock()))
-SHOW_EXPR(size_t(clu.storage_.pos))
-SHOW_EXPR(clu.storage_.rest)
-SHOW_EXPR(posOffset())
-SHOW_EXPR(slot(0))
-SHOW_EXPR(clu.numBytes())
-SHOW_EXPR(clu.numExtents())
             CHECK (blk != currBlock());                                // allocation moved to a new extent
             CHECK (getAddr(c2) == currBlock() + 2*sizeof(void*));      // c2 resides immediately after the two administrative »slots«
             CHECK (clu.storage_.rest == BLOCKSIZ - posOffset());
@@ -304,8 +288,33 @@ SHOW_EXPR(clu.numExtents())
             CHECK (c1 == 'X');
             CHECK (c2 == 'U');
             CHECK (i3 == 42);
+            
+            // allocate a "disposable" object (dtor will not be called)
+SHOW_EXPR(clu.numBytes())
+SHOW_EXPR(posOffset())
+            size_t pp = posOffset();
+            auto& o1 = clu.createDisposable<Dummy<2>> (4);
+            CHECK (o1.getID() == 4);
+SHOW_EXPR(clu.numBytes())
+SHOW_EXPR(posOffset())
+SHOW_EXPR(checksum)
+            markSum = checksum;
+            CHECK (checksum == 4+4);
+            CHECK (alignof(Dummy<2>) == alignof(char));
+            CHECK (posOffset() - pp == sizeof(Dummy<2>));
+            
+            // allocate a similar object,
+            // but this time also enrolling the destructor
+            pp = posOffset();
+            auto& o2 = clu.create<Dummy<2>> (8);
+            CHECK (o2.getID() == 8);
+            CHECK (checksum == markSum + 8+8);
+SHOW_EXPR(clu.numBytes())
+SHOW_EXPR(posOffset())
+SHOW_EXPR(checksum)
           }
-          CHECK (0==checksum);
+SHOW_EXPR(checksum)
+          CHECK (checksum == markSum);
         }
       
       

wiki/thinkPad.ichthyo.mm

@@ -81768,8 +81768,8 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
 <arrowlink COLOR="#faf8b2" DESTINATION="ID_1028046936" ENDARROW="Default" ENDINCLINATION="102;3;" ID="Arrow_ID_1495010693" STARTARROW="None" STARTINCLINATION="118;4;"/>
 </node>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716130029614" ID="ID_229036433" MODIFIED="1716130547847" TEXT="automatischer Destruktor-Aufruf">
+<node BACKGROUND_COLOR="#eef0c5" COLOR="#990000" CREATED="1716130029614" ID="ID_229036433" MODIFIED="1716604728822" TEXT="automatischer Destruktor-Aufruf">
-<icon BUILTIN="flag-yellow"/>
+<icon BUILTIN="pencil"/>
 <node CREATED="1716130041704" ID="ID_1028046936" MODIFIED="1716130101251" TEXT="kann getriggert werden von StorageManager::Destructor">
 <linktarget COLOR="#faf8b2" DESTINATION="ID_1028046936" ENDARROW="Default" ENDINCLINATION="102;3;" ID="Arrow_ID_1495010693" SOURCE="ID_350853857" STARTARROW="None" STARTINCLINATION="118;4;"/>
 </node>
@@ -81815,12 +81815,25 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
   </body>
 </html></richcontent>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716130607500" ID="ID_641247354" MODIFIED="1716130643729" TEXT="brauche somit nur noch einen Trampolin-Pointer">
+<node COLOR="#338800" CREATED="1716130607500" ID="ID_641247354" MODIFIED="1716604674352" TEXT="brauche somit nur noch einen Trampolin-Pointer">
+<icon BUILTIN="button_ok"/>
+</node>
+<node COLOR="#338800" CREATED="1716604651319" ID="ID_398123666" MODIFIED="1716604673317" TEXT="mu&#xdf; sicherstellen, da&#xdf; Destroctor-Record und Objekt beieinander liegen">
+<icon BUILTIN="button_ok"/>
+</node>
+<node BACKGROUND_COLOR="#f0d5c5" COLOR="#990033" CREATED="1716606608657" ID="ID_1834443608" MODIFIED="1716606616344" TEXT="geht das nicht einfacher und sauberer?">
+<icon BUILTIN="help"/>
+<node CREATED="1716606623571" ID="ID_1928898649" MODIFIED="1716606636617" TEXT="im Grunde ist das hier ganz gew&#xf6;hnlicher Polymorphismus"/>
+<node CREATED="1716606637660" ID="ID_1428982691" MODIFIED="1716606656903" TEXT="nur &#x201e;zu fu&#xdf;&#x201c; implementiert">
+<icon BUILTIN="stop-sign"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716606714899" ID="ID_631957038" MODIFIED="1716606741395" TEXT="der Deleter-Invoker k&#xf6;nnte durch eine VTable ersetzt werden">
 <icon BUILTIN="flag-yellow"/>
 </node>
 </node>
 </node>
 </node>
+</node>
 <node COLOR="#338800" CREATED="1716130724127" ID="ID_727448469" MODIFIED="1716133312180" TEXT="low-level-Test">
 <icon BUILTIN="button_ok"/>
 <node BACKGROUND_COLOR="#e0ceaa" COLOR="#690f14" CREATED="1716130730820" ID="ID_539013579" MODIFIED="1716130744964" TEXT="ich mache hier gef&#xe4;hrliche Sachen">
@@ -81902,8 +81915,8 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1715783068923" ID="ID_34296369" MODIFIED="1715783077530" TEXT="Tests f&#xfc;r Error-Handling zur&#xfc;ckbauen">
 <icon BUILTIN="flag-yellow"/>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716130852555" ID="ID_1309770620" MODIFIED="1716130866602" TEXT="Test f&#xfc;r interne low-level-Mechanismen">
+<node BACKGROUND_COLOR="#eef0c5" COLOR="#990000" CREATED="1716130852555" ID="ID_1309770620" MODIFIED="1716605447662" TEXT="Test f&#xfc;r interne low-level-Mechanismen">
-<icon BUILTIN="flag-yellow"/>
+<icon BUILTIN="pencil"/>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716130874040" ID="ID_253325898" MODIFIED="1716133346231" TEXT="verifyInternals">
 <arrowlink COLOR="#4173be" DESTINATION="ID_1783945506" ENDARROW="Default" ENDINCLINATION="204;17;" ID="Arrow_ID_1547348126" STARTARROW="None" STARTINCLINATION="292;-22;"/>
 <icon BUILTIN="flag-yellow"/>
@@ -81926,6 +81939,16 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
 <node COLOR="#338800" CREATED="1716552190584" ID="ID_1042988047" MODIFIED="1716593224739" TEXT="einen &#xdc;berlauf provozieren">
 <icon BUILTIN="button_ok"/>
 </node>
+<node COLOR="#338800" CREATED="1716605425287" ID="ID_1793345065" MODIFIED="1716605442774" TEXT="Objekt-Allokation mit registriertem Destruktor">
+<icon BUILTIN="button_ok"/>
+<node COLOR="#435e98" CREATED="1716605457035" ID="ID_442879470" MODIFIED="1716605483931" TEXT="sieht gut aus...">
+<node BACKGROUND_COLOR="#c8c0b6" CREATED="1716605469169" ID="ID_680488739" MODIFIED="1716605487862" TEXT="zus&#xe4;tzliche Storage belegt"/>
+<node BACKGROUND_COLOR="#c8c0b6" CREATED="1716605475561" ID="ID_43688892" MODIFIED="1716605487863" TEXT="Destruktor wird aufgerufen"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716605489686" ID="ID_838033504" MODIFIED="1716605500558" TEXT="Verzeigerung explizit verifizieren">
+<icon BUILTIN="flag-yellow"/>
+</node>
+</node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716552266490" ID="ID_34007851" MODIFIED="1716552275535" TEXT="weiteren &#xdc;berlauf mit Alignment">
 <icon BUILTIN="flag-yellow"/>
 </node>