Library: implement accounting of storage size

These diagnostics helpers must rely on low-level trickery,
since the implementation strives at avoiding unnecessary storage overhead.
Since `AllocationCluster` is move-only (for good reasons) and `StorageManager`
can not be constructed independently, a »backdoor« is created by
forced cast, relying on the known memory layout

src/lib/allocation-cluster.cpp

@@ -26,6 +26,15 @@
  ** for the render engine model. Here, in the actual translation unit, the generic part
  ** of these functions is emitted, while the corresponding header provides a strictly
  ** typed front-end, based on templates, which forward to the implementation eventually.
+ ** \par low-level trickery
+ **      The StorageManager implementation exploits object layout knowledge in order to
+ **      operate with the bare minimum of administrative overhead; notably the next allocation
+ **      is always located _within_ the current extent and by assuming that the remaining size
+ **      is tracked correctly, the start of the current extent can always be re-discovered;
+ **      the sequence of extents is managed as a linked list, where the `next*` resides in the
+ **      first »slot« within each Extent; this pointer is _dressed up_ (reinterpreted) as a
+ **      lib::LinkedElements with a heap allocator, which ends up performing the actual
+ **      allocation in blocks of EXTENT_SIZ.
  */
 
 
@@ -34,7 +43,9 @@
 #include "lib/util.hpp"
 
 
+using util::unConst;
 using util::isnil;
+using std::byte;
 
 
 namespace lib {
@@ -49,7 +60,7 @@ namespace lib {
     HeapAlloc heap;
     
     void*
-    allocate (size_t bytes)
+    allocate (size_t bytes) ////////////////////////OOO obsolete ... find a way to relocate this as custom allocator within LinkedElements!!!
     {
       return Alloc::allocate (heap, bytes);
     }
@@ -95,12 +106,14 @@ namespace lib {
       
       union ManagementView
         {
-          Storage storage{};
+          Storage storage;
           Extents extents;
         };
       
       ManagementView view_;
       
+      StorageManager()  = delete;    ///< @warning used as _overlay view_ only, never created 
+      
     public:
       static StorageManager&
       access (AllocationCluster& clu)
@@ -122,14 +135,37 @@ namespace lib {
           view_.extents.clear();
         }
       
+      size_t
+      determineExtentCnt() ///< @warning finalises current block
+        {
+          closeCurrentBlock();
+          return view_.extents.size();
+        }
+      
+      size_t
+      calcAllocInCurrentBlock()  const
+        {
+          ENSURE (STORAGE_SIZ >= view_.storage.rest);
+          return STORAGE_SIZ - view_.storage.rest;
+        }
+      
+      static auto determineStorageSize (AllocationCluster const&);
+      
     private:
+      byte*
+      getCurrentBlockStart()  const
+        {
+          return static_cast<byte*>(view_.storage.pos)
+                                  + view_.storage.rest
+                                  - EXTENT_SIZ;
+        }
+      
       void
       closeCurrentBlock()
         {
-          ASSERT (view_.storage.pos);
+          if (not view_.storage.pos) return;
           // relocate the pos-pointer to the start of the block
-          view_.storage.pos = static_cast<std::byte*>(view_.storage.pos)
+          view_.storage.pos = getCurrentBlockStart();
-                            + view_.storage.rest - EXTENT_SIZ;
           view_.storage.rest = 0;
         }
       
@@ -144,19 +180,25 @@ namespace lib {
   
   
   
-  /** creating a new AllocationCluster prepares a table capable
+  
-   *  of holding the individual object families to come. Each of those
+  
-   *  is managed by a separate instance of the low-level memory manager.
+  /**
+   * Prepare a new clustered allocation to be expanded by extents of size
+   * EXTENT_SIZ, yet discarded all at once when the dtor is called.
+   * The constructor does not allocate anything immediately.
    */
   AllocationCluster::AllocationCluster()
+    : storage_{}
     {
       TRACE (memory, "new AllocationCluster");
     }
   
   
-  /** On shutdown of the AllocationCluster we need to assure a certain
+  /**
-   *  destruction order is maintained by explicitly invoking a cleanup
+   * On shutdown of the AllocationCluster walks all extents and invokes all
-   *  operation on each of the low-level memory manager objects.
+   * registered deleter functions and then discards the complete storage.
+   * @note it is possible to allocate objects as _disposable_ — meaning
+   *       that no destructors will be enrolled and called for such objects.
    */
   AllocationCluster::~AllocationCluster()  noexcept
   try
@@ -177,7 +219,6 @@ namespace lib {
   AllocationCluster::expandStorage (size_t allocRequest)
   {
     ENSURE (allocRequest + OVERHEAD <= EXTENT_SIZ);
-    void* newBlock = allocate (EXTENT_SIZ); ////////////////////////OOO obsolete ... use ManagementView instead!!!
     StorageManager::access(*this).addBlock();
   }
 
@@ -188,19 +229,52 @@ namespace lib {
   bool
   AllocationCluster::_is_within_limits (size_t size, size_t align)
   {
-    UNIMPLEMENTED ("size limits"); ///////////////////////////OOO enforce maximum size limits
+    auto isPower2 = [](size_t n){ return !(n & (n-1)); };
+    return 0 < size
+       and 0 < align
+       and size <= STORAGE_SIZ
+       and align <= STORAGE_SIZ
+       and isPower2 (align);
   }
   
+  
+  /** @internal diagnostics helper for unit testing.
+   * Creates a shallow copy of the management data and then locates
+   * the start of the current extent to determine the allocation size
+   * @return a pair (extent-count, bytes-in-last-extent)
+   */
+  inline auto
+  AllocationCluster::StorageManager::determineStorageSize (AllocationCluster const& o)
+  {
+    size_t extents{0}, bytes{0};
+    if (o.storage_.pos)
+      {      // must manipulate pos pointer to find out count
+        Storage shallowCopy{o.storage_};
+        StorageManager& access = reinterpret_cast<StorageManager&> (shallowCopy);
+        bytes = access.calcAllocInCurrentBlock();
+        extents = access.determineExtentCnt();
+      }
+    return std::make_pair (extents, bytes);
+  }
+  
+  
   size_t
   AllocationCluster::numExtents()  const
   {
-    UNIMPLEMENTED ("Allocation management");
+    return StorageManager::determineStorageSize(*this).first;
   }
 
+  /**
+   * @warning whenever there are more than one extent,
+   *   the returned byte count is guessed only (upper bound), since
+   *   actually allocated size is not tracked to save some overhead.
+   */
   size_t
   AllocationCluster::numBytes()  const
   {
-    UNIMPLEMENTED ("Allocation management");
+    auto [extents,bytes] = StorageManager::determineStorageSize(*this);
+    return extents? bytes + (extents - 1) * STORAGE_SIZ
+                  : 0;
   }
   
   

wiki/thinkPad.ichthyo.mm

@@ -81661,8 +81661,7 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
       alignof()-Operator und die Hilfsfunktion std::align()
     </p>
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+</html></richcontent>
-</richcontent>
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 </node>
 <node CREATED="1715818964036" ID="ID_1917864530" MODIFIED="1715818999461" TEXT="bedeutet: der Offset wird justiert bis er auf einer Alignment-Grenze liegt"/>
@@ -81696,8 +81695,11 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
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+<icon BUILTIN="button_ok"/>
+</node>
+<node COLOR="#338800" CREATED="1716563047722" ID="ID_848423419" MODIFIED="1716563055539" TEXT="Storage-Diagnose">
+<icon BUILTIN="button_ok"/>
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@@ -81714,8 +81716,7 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
       auch: eine gradzahlige Anzahl an Overhead-Slots
     </p>
   </body>
-</html>
+</html></richcontent>
-</richcontent>
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 <node CREATED="1715991799166" ID="ID_1984378311" MODIFIED="1715991936313" TEXT="Trick: aktuellen Block-Start rekonstruieren">
 <richcontent TYPE="NOTE"><html>
@@ -81725,8 +81726,7 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
       ...durch diesen Trick sparen wir uns einen zus&#228;tzlichen Pointer auf den aktuellen Block: da std::allign(pos,rest) den pos-Zeiger stets koh&#228;rent zusammen mit dem rest-cnt manipuliert, k&#246;nnen wir stets aus beiden zusammen wieder zum Anfang des Blocks zur&#252;ckfinden.
     </p>
   </body>
-</html>
+</html></richcontent>
-</richcontent>
 </node>
 <node CREATED="1715991938427" ID="ID_1338480715" MODIFIED="1715991957260" TEXT="Mit einer Union lassen sich zwei verschiedene Arbeits-Modi realisieren">
 <node CREATED="1715991959415" ID="ID_143253913" MODIFIED="1715991963118" TEXT="Allokations-Modus">
@@ -81790,8 +81790,7 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
       ...da man sich diesen Code ohnehin nur anschaut, wenn man mu&#223;, ist nichts mehr gewonnen, weitere Details nochmal durch eine Indirektion zu verbergen
     </p>
   </body>
-</html>
+</html></richcontent>
-</richcontent>
 </node>
 </node>
 <node CREATED="1716130557432" ID="ID_1302192320" MODIFIED="1716130574360" TEXT="Layout-Trick: der Destructor-Descriptor liegt direkt vor dem Objekt">
@@ -81837,7 +81836,7 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
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-<node CREATED="1715790397014" ID="ID_14966020" MODIFIED="1715790537195" TEXT="Ergebnis einer Konfliktl&#xf6;sung">
+<node CREATED="1715790397014" ID="ID_14966020" LINK="#ID_869337683" MODIFIED="1715790537195" TEXT="Ergebnis einer Konfliktl&#xf6;sung">
 <richcontent TYPE="NOTE"><html>
   <head/>
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@@ -81899,6 +81898,18 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
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 <icon BUILTIN="flag-yellow"/>
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+<node BACKGROUND_COLOR="#eef0c5" COLOR="#990000" CREATED="1716552160019" ID="ID_146077309" MODIFIED="1716552282949" TEXT="die Mechanik &#xfc;berhaupt erst mal zum Laufen bekommen">
+<icon BUILTIN="pencil"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716552180480" ID="ID_1382140920" MODIFIED="1716552189738" TEXT="eine Allokation im bestehenden Extent">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716552190584" ID="ID_1042988047" MODIFIED="1716552206544" TEXT="einen &#xdc;berlauf provozieren">
+<icon BUILTIN="flag-yellow"/>
+</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>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1715782674401" ID="ID_1481008630" MODIFIED="1715782690591" TEXT="neue Tests f&#xfc;r Verwendung mit STL-Container">
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