We tried this before with a dict and for all interned strings. That ran into problems due to interpreter isolation. However, exclusively using a per-interpreter cache caused some inconsistency that can eliminate the benefit of interning. Here we circle back to using a global cache, but only for statically allocated strings. We also use a more-basic _Py_hashtable_t for that global cache instead of a dict.
Ideally we would only have the global cache, but the optional isolation of each interpreter's allocator means that a non-static string object must not outlive its interpreter. Thus we would have to store a copy of each such interned string in the global cache, tied to the main interpreter.
* No longer export most private _PyHash symbols, only export the ones
which are needed by shared extensions.
* Modules/_xxtestfuzz/fuzzer.c now uses the internal C API.
_Py_hashtable_get_entry_ptr() avoids comparing the entry hash:
compare directly keys.
Move _Py_hashtable_get_entry_ptr() just after
_Py_hashtable_get_entry_generic().
_Py_hashtable_t values become regular "void *" pointers.
* Add _Py_hashtable_entry_t.data member
* Remove _Py_hashtable_t.data_size member
* Remove _Py_hashtable_t.get_func member. It is no longer needed
to specialize _Py_hashtable_get() for a specific value size, since
all entries now have the same size (void*).
* Remove the following macros:
* _Py_HASHTABLE_GET()
* _Py_HASHTABLE_SET()
* _Py_HASHTABLE_SET_NODATA()
* _Py_HASHTABLE_POP()
* Rename _Py_hashtable_pop() to _Py_hashtable_steal()
* _Py_hashtable_foreach() callback now gets key and value rather than
entry.
* Remove _Py_hashtable_value_destroy_func type. value_destroy_func
callback now only has a single parameter: data (void*).
Rewrite _tracemalloc to store "trace_t*" rather than directly
"trace_t" in traces hash tables. Traces are now allocated on the heap
memory, outside the hash table.
Add tracemalloc_copy_traces() and tracemalloc_copy_domains() helper
functions.
Remove _Py_hashtable_copy() function since there is no API to copy a
key or a value.
Remove also _Py_hashtable_delete() function which was commented.
Rewrite _Py_hashtable_t type to always store the key as
a "const void *" pointer. Add an explicit "key" member to
_Py_hashtable_entry_t.
Remove _Py_hashtable_t.key_size member.
hash and compare functions drop their hash table parameter, and their
'key' parameter type becomes "const void *".
Add a new _Py_HashPointerRaw() function which avoids replacing -1
with -2 to micro-optimize hash table using pointer keys: using
_Py_hashtable_hash_ptr() hash function.
Optimize _Py_hashtable_get() and _Py_hashtable_get_entry() for
pointer keys:
* key_size == sizeof(void*)
* hash_func == _Py_hashtable_hash_ptr
* compare_func == _Py_hashtable_compare_direct
Changes:
* Add get_func and get_entry_func members to _Py_hashtable_t
* Convert _Py_hashtable_get() and _Py_hashtable_get_entry() functions
to static nline functions.
* Add specialized get and get entry for pointer keys.
_Py_hashtable_new() now uses PyMem_Malloc/PyMem_Free allocator by
default, rather than PyMem_RawMalloc/PyMem_RawFree.
PyMem_Malloc is faster than PyMem_RawMalloc for memory blocks smaller
than or equal to 512 bytes.
* Move Modules/hashtable.h to Include/internal/pycore_hashtable.h
* Move Modules/hashtable.c to Python/hashtable.c
* Python is now linked to hashtable.c. _tracemalloc is no longer
linked to hashtable.c. Previously, marshal.c got hashtable.c via
_tracemalloc.c which is built as a builtin module.
