Issue #18874: Implement the PEP 454 (tracemalloc)
diff --git a/Modules/hashtable.h b/Modules/hashtable.h
new file mode 100644
index 0000000..539e490
--- /dev/null
+++ b/Modules/hashtable.h
@@ -0,0 +1,128 @@
+#ifndef Py_HASHTABLE_H
+#define Py_HASHTABLE_H
+
+/* The whole API is private */
+#ifndef Py_LIMITED_API
+
+typedef struct _Py_slist_item_s {
+    struct _Py_slist_item_s *next;
+} _Py_slist_item_t;
+
+typedef struct {
+    _Py_slist_item_t *head;
+} _Py_slist_t;
+
+#define _Py_SLIST_ITEM_NEXT(ITEM) (((_Py_slist_item_t *)ITEM)->next)
+
+#define _Py_SLIST_HEAD(SLIST) (((_Py_slist_t *)SLIST)->head)
+
+typedef struct {
+    /* used by _Py_hashtable_t.buckets to link entries */
+    _Py_slist_item_t _Py_slist_item;
+
+    const void *key;
+    Py_uhash_t key_hash;
+
+    /* data follows */
+} _Py_hashtable_entry_t;
+
+#define _PY_HASHTABLE_ENTRY_DATA(ENTRY) \
+        ((char *)(ENTRY) + sizeof(_Py_hashtable_entry_t))
+
+#define _Py_HASHTABLE_ENTRY_DATA_AS_VOID_P(ENTRY) \
+        (*(void **)_PY_HASHTABLE_ENTRY_DATA(ENTRY))
+
+#define _Py_HASHTABLE_ENTRY_READ_DATA(TABLE, DATA, DATA_SIZE, ENTRY) \
+    do { \
+        assert((DATA_SIZE) == (TABLE)->data_size); \
+        memcpy(DATA, _PY_HASHTABLE_ENTRY_DATA(ENTRY), DATA_SIZE); \
+    } while (0)
+
+typedef Py_uhash_t (*_Py_hashtable_hash_func) (const void *key);
+typedef int (*_Py_hashtable_compare_func) (const void *key, const _Py_hashtable_entry_t *he);
+typedef void* (*_Py_hashtable_copy_data_func)(void *data);
+typedef void (*_Py_hashtable_free_data_func)(void *data);
+typedef size_t (*_Py_hashtable_get_data_size_func)(void *data);
+
+typedef struct {
+    /* allocate a memory block */
+    void* (*malloc) (size_t size);
+
+    /* release a memory block */
+    void (*free) (void *ptr);
+} _Py_hashtable_allocator_t;
+
+typedef struct {
+    size_t num_buckets;
+    size_t entries; /* Total number of entries in the table. */
+    _Py_slist_t *buckets;
+    size_t data_size;
+
+    _Py_hashtable_hash_func hash_func;
+    _Py_hashtable_compare_func compare_func;
+    _Py_hashtable_copy_data_func copy_data_func;
+    _Py_hashtable_free_data_func free_data_func;
+    _Py_hashtable_get_data_size_func get_data_size_func;
+    _Py_hashtable_allocator_t alloc;
+} _Py_hashtable_t;
+
+/* hash and compare functions for integers and pointers */
+PyAPI_FUNC(Py_uhash_t) _Py_hashtable_hash_ptr(const void *key);
+PyAPI_FUNC(Py_uhash_t) _Py_hashtable_hash_int(const void *key);
+PyAPI_FUNC(int) _Py_hashtable_compare_direct(const void *key, const _Py_hashtable_entry_t *entry);
+
+PyAPI_FUNC(_Py_hashtable_t *) _Py_hashtable_new(
+    size_t data_size,
+    _Py_hashtable_hash_func hash_func,
+    _Py_hashtable_compare_func compare_func);
+PyAPI_FUNC(_Py_hashtable_t *) _Py_hashtable_new_full(
+    size_t data_size,
+    size_t init_size,
+    _Py_hashtable_hash_func hash_func,
+    _Py_hashtable_compare_func compare_func,
+    _Py_hashtable_copy_data_func copy_data_func,
+    _Py_hashtable_free_data_func free_data_func,
+    _Py_hashtable_get_data_size_func get_data_size_func,
+    _Py_hashtable_allocator_t *allocator);
+PyAPI_FUNC(_Py_hashtable_t *) _Py_hashtable_copy(_Py_hashtable_t *src);
+PyAPI_FUNC(void) _Py_hashtable_clear(_Py_hashtable_t *ht);
+PyAPI_FUNC(void) _Py_hashtable_destroy(_Py_hashtable_t *ht);
+
+typedef int (*_Py_hashtable_foreach_func) (_Py_hashtable_entry_t *entry, void *arg);
+
+PyAPI_FUNC(int) _Py_hashtable_foreach(
+    _Py_hashtable_t *ht,
+    _Py_hashtable_foreach_func func, void *arg);
+PyAPI_FUNC(size_t) _Py_hashtable_size(_Py_hashtable_t *ht);
+
+PyAPI_FUNC(_Py_hashtable_entry_t*) _Py_hashtable_get_entry(
+    _Py_hashtable_t *ht,
+    const void *key);
+PyAPI_FUNC(int) _Py_hashtable_set(
+    _Py_hashtable_t *ht,
+    const void *key,
+    void *data,
+    size_t data_size);
+PyAPI_FUNC(int) _Py_hashtable_get(
+    _Py_hashtable_t *ht,
+    const void *key,
+    void *data,
+    size_t data_size);
+PyAPI_FUNC(int) _Py_hashtable_pop(
+    _Py_hashtable_t *ht,
+    const void *key,
+    void *data,
+    size_t data_size);
+PyAPI_FUNC(void) _Py_hashtable_delete(
+    _Py_hashtable_t *ht,
+    const void *key);
+
+#define _Py_HASHTABLE_SET(TABLE, KEY, DATA) \
+    _Py_hashtable_set(TABLE, KEY, &(DATA), sizeof(DATA))
+
+#define _Py_HASHTABLE_GET(TABLE, KEY, DATA) \
+    _Py_hashtable_get(TABLE, KEY, &(DATA), sizeof(DATA))
+
+#endif   /* Py_LIMITED_API */
+
+#endif