tqchen commented on code in PR #593:
URL: https://github.com/apache/tvm-ffi/pull/593#discussion_r3295117594
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include/tvm/ffi/c_api.h:
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@@ -580,6 +580,83 @@ TVM_FFI_DLL int TVMFFIObjectDecRef(TVMFFIObjectHandle obj);
TVM_FFI_DLL int TVMFFIObjectCreateOpaque(void* handle, int32_t type_index,
void (*deleter)(void* handle),
TVMFFIObjectHandle* out);
+//-----------------------------------------------------------------------
+// Section: Custom allocator hook for Object allocations
+//
+// Frontends (Python, Rust, etc.) can register a custom allocator that the
+// core ObjAllocator consults inside make_object<T> /
make_inplace_array_object.
+// When a custom allocator is registered, every allocation of a ref-counted
+// Object is given the allocator's chance to prepend bookkeeping bytes ahead
+// of the object. The allocator returns the address of the embedded T
+// (= Object = TVMFFIObject); immediately before that address it must place a
+// TVMFFICustomAllocHeader whose ``delete_space`` field is invoked from the
+// C++ Weak deleter to release the entire block.
+//
+// The core libtvm_ffi.so does not depend on Python (or any other frontend).
+// libtvm_ffi installs a builtin default allocator at registry init time, so
+// every Object allocation always carries at least the base
+// TVMFFICustomAllocHeader; frontends that need richer per-allocation
+// bookkeeping (e.g. Python's ``py_object`` back-pointer) override the global
+// default with their own allocator.
+//-----------------------------------------------------------------------
+/*!
+ * \brief Header that sits immediately before the embedded TVMFFIObject. The
+ * C++ deleter recovers this header by walking back a fixed offset
+ * (``sizeof(TVMFFICustomAllocHeader)``) from the TVMFFIObject pointer
+ * and invokes ``delete_space``.
+ *
+ * Frontends are free to define a derived layout that places extra fields
+ * before this base; the derived ``delete_space`` callback is responsible for
+ * recovering its enclosing struct from the ``tptr`` argument. Frontends can
+ * detect their own allocations by comparing this header's ``delete_space``
+ * pointer against their own callback (no flag bit needed).
+ */
+typedef struct {
+ /*!
+ * \brief Free the allocation that contains ``tptr``.
+ * \param tptr The pointer originally returned by
+ * ``TVMFFICustomAllocator::allocate`` (i.e. the address of T,
+ * not the start of the underlying malloc block).
+ */
+ void (*delete_space)(void* tptr);
+} TVMFFICustomAllocHeader;
+
+/*!
+ * \brief Custom allocator entry registered with TVMFFISetCustomAllocator.
+ */
+typedef struct {
+ /*!
+ * \brief Allocate ``size`` bytes for an Object of ``type_index`` with the
+ * requested ``alignment``. Implementations must place a
+ * TVMFFICustomAllocHeader immediately before the returned pointer
+ * (at the fixed base offset documented on TVMFFICustomAllocHeader)
+ * with a non-NULL ``delete_space``.
+ * \return Pointer to T's location (treated as TVMFFIObject* by the caller).
+ */
+ void* (*allocate)(size_t size, size_t alignment, int32_t type_index);
Review Comment:
it is helpful to include
```c++
void* (*allocate)(size_t size, size_t alignment, int32_t type_index, void*
context);
void* context;
```
This helps to future proof case that needs a caller
Need to document the error behavior, when error, return NULL, and error is
set through TVMFFIErrorSetRaised
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