[sqlite3] drop statement in_use field in favour of sqlite3_stmt_busy()

[erlend-aasland]

BPO	44073
Nosy	@berkerpeksag, @serhiy-storchaka, @erlend-aasland
PRs	gh-88239: Use sqlite3_stmt_busy() to determine if statements are in use #25984

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/erlend-aasland'
closed_at = None
created_at = <Date 2021-05-08.07:47:59.789>
labels = ['extension-modules', 'easy', 'type-feature', '3.11']
title = '[sqlite3] drop statement in_use field in favour of sqlite3_stmt_busy()'
updated_at = <Date 2021-08-19.20:10:44.154>
user = 'https://github.com/erlend-aasland'

bugs.python.org fields:

activity = <Date 2021-08-19.20:10:44.154>
actor = 'erlendaasland'
assignee = 'erlendaasland'
closed = False
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2021-05-08.07:47:59.789>
creator = 'erlendaasland'
dependencies = []
files = []
hgrepos = []
issue_num = 44073
keywords = ['patch', 'easy (C)']
message_count = 3.0
messages = ['393241', '393243', '399932']
nosy_count = 3.0
nosy_names = ['berker.peksag', 'serhiy.storchaka', 'erlendaasland']
pr_nums = ['25984']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44073'
versions = ['Python 3.11']

[erlend-aasland]

sqlite3_stmt_busy() has been around since SQLite 3.7.10. I suggest to drop the in_use field of pysqlite_Statement in favour of sqlite3_stmt_busy(); we do not need to duplicate functionality already present in SQLite.

There was a bugfix for sqlite3_stmt_busy() in SQLite 3.8.6 regarding rollback statements, but we normally reset all our statements after use, so it should not be a problem. There are some corner cases in _pysqlite_query_execute() where a sqlite3_stmt may not be reset upon return, but that's easily fixable (and it would be a nice side-effect).

Pro's:

• statement objects have one less member
• no duplication of SQLite functionality
• cleaner exit paths from _pysqlite_query_execute()
• less lines of code, easier to maintain

Con's:

• the current code works / "code churn"

[erlend-aasland]

$ git diff --stat
 Modules/_sqlite/connection.c |  1 -
 Modules/_sqlite/cursor.c     |  5 +

---

Modules/_sqlite/statement.c | 14 +-------------
Modules/_sqlite/statement.h | 2 --
4 files changed, 2 insertions(+), 20 deletions(-)

[erlend-aasland]

See also gh-89121 (bpo-44958)