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

报告指出，长期存在的连接上的 sqlite3 Blob 对象注册了 weakrefs，并链接到 PR gh-144435。首先检查 Blob 的 weakref 注册以及报告中提到的相关 weakref-cleanup 模式，然后运行提供的复现程序，以确认已失效的引用是否会停止累积；请与链接的 PR 协作，而不要重复工作。