Revert "disk cache: thread-local db conn (#17694)"

This reverts commit 11edcc144c.

tinygrad/helpers.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 import time
 START_TIME = time.perf_counter()
-import os, functools, re, contextlib, operator, hashlib, pickle, sqlite3, tempfile, pathlib, string, ctypes, sys, gzip, getpass, gc, threading
+import os, functools, re, contextlib, operator, hashlib, pickle, sqlite3, tempfile, pathlib, string, ctypes, sys, gzip, getpass, gc
 from collections import defaultdict
 import shutil, math, types, copyreg, inspect, importlib, decimal, itertools, difflib
 from dataclasses import dataclass, field, replace
@@ -398,17 +398,18 @@ cache_dir: str = os.path.join(getenv("XDG_CACHE_HOME", os.path.expanduser("~/Lib
 CACHEDB: str = getenv("CACHEDB", os.path.abspath(os.path.join(cache_dir, "cache.db")))
 
 VERSION = 22
-_db_connection = threading.local()
+_db_connection = None
 def db_connection():
-  if (conn:=getattr(_db_connection, "conn", None)) is None:
+  global _db_connection
+  if _db_connection is None:
     os.makedirs(CACHEDB.rsplit(os.sep, 1)[0], exist_ok=True)
-    conn = _db_connection.conn = sqlite3.connect(CACHEDB, timeout=60, isolation_level="IMMEDIATE")
+    _db_connection = sqlite3.connect(CACHEDB, timeout=60, isolation_level="IMMEDIATE")
     # another connection has set it already or is in the process of setting it
     # that connection will lock the database
-    with contextlib.suppress(sqlite3.OperationalError): conn.execute("PRAGMA journal_mode=WAL").fetchone()
-    conn.execute("PRAGMA synchronous=NORMAL")
-    if DEBUG >= 8: conn.set_trace_callback(print)
-  return conn
+    with contextlib.suppress(sqlite3.OperationalError): _db_connection.execute("PRAGMA journal_mode=WAL").fetchone()
+    _db_connection.execute("PRAGMA synchronous=NORMAL")
+    if DEBUG >= 8: _db_connection.set_trace_callback(print)
+  return _db_connection
 
 def diskcache_clear():
   cur = db_connection().cursor()