sqlite3 Blob objects leave behind weakrefs which are never cleaned up

Bug report

Bug description:

The sqlite3 Blob class registers a weakref to itself on the Connection it came from. These are added to a list and never cleaned up, so if you have a long-lived connection and call .blobopen() repeatedly, you gradually accumulate ever more dead weakrefs.

It looks like the blob weakrefs were added to match a similar system for weakrefs (removed in #144378), but the code to periodically clear out dead weakrefs was missed.

import gc
import sqlite3

conn = sqlite3.connect(":memory:")
conn.execute("CREATE TABLE foo(a INTEGER PRIMARY KEY, b BLOB)")
conn.execute("INSERT INTO foo VALUES(NULL, ?)", (b'abcdefpokpokpko',))
conn.commit()

# Create & destroy many Blob objects
for _ in range(10_000):
    conn.blobopen("foo", "b", 1)

# Get a reference to the internal list of blob weakrefs - you may need to play with the index here
blob_list = gc.get_referents(conn)[-3]
print(len(blob_list))

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-144435

報告指出，長期存在的連線上的 sqlite3 Blob 物件註冊了 weakrefs，並連結到 PR gh-144435。首先檢查 Blob 的 weakref 註冊以及報告中提到的相關 weakref-cleanup 模式，然後執行提供的重現程式，以確認已失效的參照是否會停止累積；請與連結的 PR 協作，而不要重複工作。