added a function pointer field to CpuStorageObj for custom destructio…

…n logic

src/arraymancer/laser/tensor/datatypes.nim

@@ -40,9 +40,10 @@ type
   CpuStorageObj[T] {.shallow.} = object
     # Workaround supportsCopyMem in type section - https://github.com/nim-lang/Nim/issues/13193
     when T is KnownSupportsCopyMem:
-      raw_buffer*: ptr UncheckedArray[T] # 8 bytes
-      memalloc*: pointer                 # 8 bytes
-      isMemOwner*: bool                  # 1 byte
+      raw_buffer*: ptr UncheckedArray[T]                               # 8 bytes
+      memalloc*: pointer                                               # 8 bytes
+      isMemOwner*: bool                                                # 1 byte
+      deleter*: proc(memalloc: pointer) {.noconv, gcsafe, raises: [].} # 8 bytes
     else: # Tensors of strings, other ref types or non-trivial destructors
       raw_buffer*: seq[T]                # 8 bytes (16 for seq v2 backed by destructors?)
 
@@ -74,14 +75,21 @@ when not defined(gcDestructors):
   proc finalizer[T](storage: CpuStorage[T]) =
     static: assert T is KnownSupportsCopyMem, "Tensors of seq, strings, ref types and types with non-trivial destructors cannot be finalized by this proc"
     if storage.isMemOwner and not storage.memalloc.isNil:
-      storage.memalloc.deallocShared()
+      if storage.deleter.isNil:
+        storage.memalloc.deallocShared()
+      else:
+        storage.deleter(storage.memalloc)
+        storage.deleter = nil
       storage.memalloc = nil
 else:
   when (NimMajor, NimMinor, NimPatch) >= (2, 0, 0):
     proc `=destroy`[T](storage: CpuStorageObj[T]) =
       when T is KnownSupportsCopyMem:
         if storage.isMemOwner and not storage.memalloc.isNil:
-          storage.memalloc.deallocShared()
+          if storage.deleter.isNil:
+            storage.memalloc.deallocShared()
+          else:
+            storage.deleter(storage.memalloc)
       else:
         # The following cast removes the following warning:
         # =destroy(storage.raw_buffer) can raise an unlisted exception: Exception
@@ -91,7 +99,11 @@ else:
     proc `=destroy`[T](storage: var CpuStorageObj[T]) =
       when T is KnownSupportsCopyMem:
         if storage.isMemOwner and not storage.memalloc.isNil:
-          storage.memalloc.deallocShared()
+          if storage.deleter.isNil:
+            storage.memalloc.deallocShared()
+          else:
+            storage.deleter(storage.memalloc)
+            storage.deleter = nil
           storage.memalloc = nil
       else:
         `=destroy`(storage.raw_buffer)
@@ -113,6 +125,7 @@ proc allocCpuStorage*[T](storage: var CpuStorage[T], size: int) =
     storage.memalloc = allocShared(sizeof(T) * size + LASER_MEM_ALIGN - 1)
     storage.isMemOwner = true
     storage.raw_buffer = align_raw_data(T, storage.memalloc)
+    storage.deleter = nil
   else: # Always 0-initialize Tensors of seq, strings, ref types and types with non-trivial destructors
     new(storage)
     storage.raw_buffer.newSeq(size)
@@ -133,6 +146,25 @@ proc cpuStorageFromBuffer*[T: KnownSupportsCopyMem](
   storage.memalloc = rawBuffer
   storage.isMemOwner = false
   storage.raw_buffer = cast[ptr UncheckedArray[T]](storage.memalloc)
+  storage.deleter = nil
+
+proc cpuStorageFromBuffer*[T: KnownSupportsCopyMem](
+    storage: var CpuStorage[T],
+    rawBuffer: pointer,
+    memalloc: pointer,
+    deleter: proc(memalloc: pointer) {.noconv, gcsafe, raises: [].}) =
+  ## Create a `CpuStorage`, which stores data from a given raw pointer, which
+  ## it will own. The destructor/finalizer will do a `deleter(memalloc)` call.
+  ##
+  ## The input buffer must be a raw `pointer`.
+  when not defined(gcDestructors):
+    new(storage, finalizer[T])
+  else:
+    new(storage)
+  storage.memalloc = memalloc
+  storage.isMemOwner = true
+  storage.raw_buffer = cast[ptr UncheckedArray[T]](rawBuffer)
+  storage.deleter = deleter
 
 func is_C_contiguous*(t: Tensor): bool =
   ## Check if the tensor follows C convention / is row major