Move global user storage from WeakValueDictionary to dict

Profiling showed that WeakValueDictionary caused rather significant
and noticeable slowdowns during startup. Since the only thing it was
used for was to automatically remove the key from the mapping when
the reference count reaches zero, the same could theoretically be
accomplished by using the __del__ special method. There is a chance
that this could lead to a memory leak since the __del__ method is not
always called, but the only instances of this happening are during
interpreter shutdown to my knowledge and at that point the mapping
is the least of my concern.

discord/state.py

@@ -28,7 +28,7 @@ import copy
 import datetime
 import itertools
 import logging
-from typing import Optional
+from typing import Dict, Optional
 import weakref
 import warnings
 import inspect
@@ -58,7 +58,6 @@ from .interactions import Interaction
 from .ui.view import ViewStore
 from .stage_instance import StageInstance
 from .threads import Thread, ThreadMember
-from discord import guild
 
 class ChunkRequest:
     def __init__(self, guild_id, loop, resolver, *, cache=True):
@@ -181,6 +180,7 @@ class ConnectionState:
 
         if not intents.members or cache_flags._empty:
             self.store_user = self.store_user_no_intents
+            self.deref_user = self.deref_user_no_intents
 
         self.parsers = parsers = {}
         for attr, func in inspect.getmembers(self):
@@ -191,7 +191,19 @@ class ConnectionState:
 
     def clear(self):
         self.user = None
-        self._users = weakref.WeakValueDictionary()
+        # Originally, this code used WeakValueDictionary to maintain references to the
+        # global user mapping.
+
+        # However, profiling showed that this came with two cons:
+
+        # 1. The __weakref__ slot caused a non-trivial increase in memory
+        # 2. The performance of the mapping caused store_user to be a bottleneck.
+
+        # Since this is undesirable, a mapping is now used instead with stored
+        # references now using a regular dictionary with eviction being done
+        # using __del__. Testing this for memory leaks led to no discernable leaks,
+        # though more testing will have to be done.
+        self._users: Dict[int, User] = {}
         self._emojis = {}
         self._guilds = {}
         self._view_store = ViewStore(self)
@@ -265,7 +277,6 @@ class ConnectionState:
             vc.main_ws = ws
 
     def store_user(self, data):
-        # this way is 300% faster than `dict.setdefault`.
         user_id = int(data['id'])
         try:
             return self._users[user_id]
@@ -273,11 +284,18 @@ class ConnectionState:
             user = User(state=self, data=data)
             if user.discriminator != '0000':
                 self._users[user_id] = user
+                user._stored = True
             return user
 
+    def deref_user(self, user_id):
+        self._users.pop(user_id, None)
+
     def store_user_no_intents(self, data):
         return User(state=self, data=data)
 
+    def deref_user_no_intents(self, user_id):
+        return
+
     def get_user(self, id):
         return self._users.get(id)
 
@@ -461,7 +479,7 @@ class ConnectionState:
         self._ready_state = asyncio.Queue()
         self.clear()
         self.user = user = ClientUser(state=self, data=data['user'])
-        self._users[user.id] = user
+        self.store_user(data['user'])
 
         if self.application_id is None:
             try:
@@ -632,6 +650,9 @@ class ConnectionState:
 
     def parse_user_update(self, data):
         self.user._update(data)
+        ref = self._users.get(self.user.id)
+        if ref:
+            ref._update(data)
 
     def parse_invite_create(self, data):
         invite = Invite.from_gateway(state=self, data=data)

discord/user.py

@@ -322,11 +322,28 @@ class User(BaseUser, discord.abc.Messageable):
         Specifies if the user is a system user (i.e. represents Discord officially).
     """
 
-    __slots__ = ('__weakref__',)
+    __slots__ = ('_stored',)
+
+    def __init__(self, *, state, data):
+        super().__init__(state=state, data=data)
+        self._stored = False
 
     def __repr__(self):
         return f'<User id={self.id} name={self.name!r} discriminator={self.discriminator!r} bot={self.bot}>'
 
+    def __del__(self) -> None:
+        try:
+            if self._stored:
+                self._state.deref_user(self.id)
+        except Exception:
+            pass
+
+    @classmethod
+    def _copy(cls, user):
+        self = super()._copy(user)
+        self._stored = getattr(user, '_stored', False)
+        return self
+
     async def _get_channel(self):
         ch = await self.create_dm()
         return ch