代码之家 › 专栏 › 技术社区 › aaronasterling

使用sqlite3包在python中的不同线程之间共享:内存:数据库

python-multithreading sqlite3 sqlite python

aaronasterling · 技术社区 · 16 年前

我想用python创建一个:memory:数据库,并从不同的线程访问它。基本上类似于:

class T(threading.Thread):
    def run(self):
        self.conn = sqlite3.connect(':memory:')
        # do stuff with the database

for i in xrange(N):
    T().start()

我知道过去了 check_same_thread=True 线程之间的连接,但希望尽可能避免这样做。谢谢你的帮助。

2 回复 | 直到 16 年前

toriningen 15 年前

如果不破解sqlite3库本身,就不能重用它 :memory: 数据库,因为它保证对每个连接都是独占和私有的。要破解它的访问权限,请仔细查看 src/pager.c :memory:00 , :memory:something , :memory:okay_hai pPager->memDb 指针通过一些简单的C端映射。

toriningen 10 年前

import sqlite3

foobar_uri = 'file:foobar_database?mode=memory&cache=shared'
not_really_foobar_uri = 'file:not_really_foobar?mode=memory&cache=shared'

# connect to databases in no particular order
db2 = sqlite3.connect(foobar_uri, uri=True)
db_lol = sqlite3.connect(not_really_foobar_uri, uri=True)
db1 = sqlite3.connect(foobar_uri, uri=True)

# create cursor as db2
cur2 = db2.cursor()

# create table as db2
db2.execute('CREATE TABLE foo (NUMBER bar)')

# insert values as db1
db1.execute('INSERT INTO foo VALUES (42)')
db1.commit()

# and fetch them from db2 through cur2
cur2.execute('SELECT * FROM foo')
print(cur2.fetchone()[0])  # 42

# test that db_lol is not shared with db1 and db2
try:
    db_lol.cursor().execute('SELECT * FROM foo')
except sqlite3.OperationalError as exc:
    print(exc)  # just as expected

数据库访问故意纠缠在一起,以表明从SQLite的角度来看,到内存中数据库的两个同名连接是相同的。

参考文献:

sqlite3 模块仍然能够导入APSW连接,这可以用来实现相同的效果。这是投递 sqlite3公司

from sqlite3 import *
from sqlite3 import connect as _connect
from apsw import Connection as _ApswConnection
from apsw import SQLITE_OPEN_READWRITE as _SQLITE_OPEN_READWRITE
from apsw import SQLITE_OPEN_CREATE as _SQLITE_OPEN_CREATE
from apsw import SQLITE_OPEN_URI as _SQLITE_OPEN_URI

# APSW and pysqlite use different instances of sqlite3 library, so initializing
# APSW won't help pysqlite. Because pysqlite does not expose any way to
# explicitly call sqlite3_initialize(), here goes an ugly hack. This only has
# to be done once per process.
_connect(':memory:').close()

def connect(database, timeout=5.0, detect_types=0, isolation_level=None,
            check_same_thread=True, factory=Connection, cached_statements=100,
            uri=False):
    flags = _SQLITE_OPEN_READWRITE | _SQLITE_OPEN_CREATE

    if uri:
        flags |= _SQLITE_OPEN_URI

    db = _ApswConnection(database, flags, None, cached_statements)
    conn = _connect(db, timeout, detect_types, isolation_level, 
                    check_same_thread, factory, cached_statements)

    return conn