add mi_new_realloc(n) to support C++ style reallocation that raises std::bad_alloc on out-of-memory

include/mimalloc.h

@@ -341,11 +341,15 @@ mi_decl_export void mi_free_size(void* p, size_t size) mi_attr_noexcept;
 mi_decl_export void mi_free_size_aligned(void* p, size_t size, size_t alignment) mi_attr_noexcept;
 mi_decl_export void mi_free_aligned(void* p, size_t alignment) mi_attr_noexcept;
 
+// The `mi_new` wrappers implement C++ semantics on out-of-memory instead of directly returning `NULL`.
+// (and call `std::get_new_handler` and potentially raise a `std::bad_alloc` exception).
 mi_decl_export void* mi_new(size_t size) mi_attr_malloc mi_attr_alloc_size(1);
-mi_decl_export void* mi_new_n(size_t count, size_t size) mi_attr_malloc mi_attr_alloc_size2(1,2);
 mi_decl_export void* mi_new_aligned(size_t size, size_t alignment) mi_attr_malloc mi_attr_alloc_size(1) mi_attr_alloc_align(2);
 mi_decl_export void* mi_new_nothrow(size_t size) mi_attr_malloc mi_attr_alloc_size(1);
 mi_decl_export void* mi_new_aligned_nothrow(size_t size, size_t alignment) mi_attr_malloc mi_attr_alloc_size(1) mi_attr_alloc_align(2);
+mi_decl_export void* mi_new_n(size_t count, size_t size) mi_attr_malloc mi_attr_alloc_size2(1, 2);
+mi_decl_export void* mi_new_realloc(void* p, size_t newsize) mi_attr_malloc mi_attr_alloc_size(2);
+mi_decl_export void* mi_new_reallocn(void* p, size_t newcount, size_t size) mi_attr_malloc mi_attr_alloc_size2(2, 3);
 
 #ifdef __cplusplus
 }

src/alloc.c

@@ -721,3 +721,22 @@ void* mi_new_n(size_t count, size_t size) {
     return mi_new(total);
   }
 }
+
+void* mi_new_realloc(void* p, size_t newsize) {
+  void* q;
+  do {
+    q = mi_realloc(p, newsize);
+  } while (q == NULL && mi_try_new_handler(false));
+  return q;
+}
+
+void* mi_new_reallocn(void* p, size_t newcount, size_t size) {
+  size_t total;
+  if (mi_unlikely(mi_count_size_overflow(newcount, size, &total))) {
+    mi_try_new_handler(false);  // on overflow we invoke the try_new_handler once to potentially throw std::bad_alloc
+    return NULL;
+  }
+  else {
+    return mi_new_realloc(p, total);
+  }
+}