Factor out SQL retries
Test if sqlite is multithreading-safe and bail out if not. sqlite versions since at least 2008 are. But, as it still causes errors when 2 threads try to write to the same connection simultanously (We get a "cannot start transaction within a transaction" error), we protect writes with a per class, ie per-connection lock. Factor out the retrying to write when the database is locked. Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de> Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>
This commit is contained in:
Sebastian Spaeth
Nicolas Sebrecht
parent
af25c2779f
commit
0af9ef70a7
@ -16,15 +16,29 @@
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# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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import os.path
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import re
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from threading import Lock
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from LocalStatus import LocalStatusFolder, magicline
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try:
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from pysqlite2 import dbapi2 as sqlite
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import sqlite3 as sqlite
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except:
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pass #fail only if needed later on, not on import
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class LocalStatusSQLiteFolder(LocalStatusFolder):
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"""LocalStatus backend implemented with an SQLite database"""
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#current version of the db format
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"""LocalStatus backend implemented with an SQLite database
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As python-sqlite currently does not allow to access the same sqlite
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objects from various threads, we need to open get and close a db
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connection and cursor for all operations. This is a big disadvantage
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and we might want to investigate if we cannot hold an object open
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for a thread somehow."""
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#though. According to sqlite docs, you need to commit() before
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#the connection is closed or your changes will be lost!"""
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#get db connection which autocommits
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#connection = sqlite.connect(self.filename, isolation_level=None)
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#cursor = connection.cursor()
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#return connection, cursor
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#current version of our db format
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cur_version = 1
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def __init__(self, root, name, repository, accountname, config):
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@ -32,33 +46,68 @@ class LocalStatusSQLiteFolder(LocalStatusFolder):
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repository,
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accountname,
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config)
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#Try to establish connection
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# dblock protects against concurrent writes in same connection
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self._dblock = Lock()
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#Try to establish connection, no need for threadsafety in __init__
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try:
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self.connection = sqlite.connect(self.filename)
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self.connection = sqlite.connect(self.filename, check_same_thread = False)
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except NameError:
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# sqlite import had failed
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raise UserWarning('SQLite backend chosen, but no sqlite python '
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'bindings available. Please install.')
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#Test if the db version is current enough and if the db is
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#readable.
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#Make sure sqlite is in multithreading SERIALIZE mode
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assert sqlite.threadsafety == 1, 'Your sqlite is not multithreading safe.'
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#Test if db version is current enough and if db is readable.
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try:
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self.cursor = self.connection.cursor()
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self.cursor.execute("SELECT value from metadata WHERE key='db_version'")
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cursor = self.connection.execute("SELECT value from metadata WHERE key='db_version'")
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except sqlite.DatabaseError:
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#db file missing or corrupt, recreate it.
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self.connection.close()
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self.upgrade_db(0)
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else:
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# fetch db version and upgrade if needed
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version = int(self.cursor.fetchone()[0])
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self.cursor.close()
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version = int(cursor.fetchone()[0])
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if version < LocalStatusSQLiteFolder.cur_version:
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self.upgrade_db(version)
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self.connection.close()
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def sql_write(self, sql, vars=None):
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"""execute some SQL retrying if the db was locked.
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:param sql: the SQL string passed to execute() :param args: the
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variable values to `sql`. E.g. (1,2) or {uid:1, flags:'T'}. See
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sqlite docs for possibilities.
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:returns: the Cursor() or raises an Exception"""
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success = False
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while not success:
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self._dblock.acquire()
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try:
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if vars is None:
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cursor = self.connection.execute(sql)
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else:
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cursor = self.connection.execute(sql, vars)
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success = True
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self.connection.commit()
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except sqlite.OperationalError, e:
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if e.args[0] == 'cannot commit - no transaction is active':
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pass
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elif e.args[0] == 'database is locked':
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self.ui.debug('', "Locked sqlite database, retrying.")
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success = False
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else:
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raise
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finally:
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self._dblock.release()
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return cursor
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def upgrade_db(self, from_ver):
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"""Upgrade the sqlite format from version 'from_ver' to current"""
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if hasattr(self, 'connection'):
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self.connection.close() #close old connections first
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self.connection = sqlite.connect(self.filename, check_same_thread = False)
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if from_ver == 0:
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# from_ver==0: no db existent: plain text migration?
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self.create_db()
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@ -74,22 +123,18 @@ class LocalStatusSQLiteFolder(LocalStatusFolder):
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(self.repository, self))
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file = open(plaintextfilename, "rt")
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line = file.readline().strip()
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assert(line == magicline)
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connection = sqlite.connect(self.filename)
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cursor = connection.cursor()
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data = []
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for line in file.xreadlines():
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line = line.strip()
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uid, flags = line.split(':')
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uid, flags = line.strip().split(':')
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uid = long(uid)
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flags = [x for x in flags]
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flags.sort()
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flags = ''.join(flags)
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self.cursor.execute('INSERT INTO status (id,flags) VALUES (?,?)',
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(uid,flags))
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file.close()
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flags = list(flags)
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flags = ''.join(sorted(flags))
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data.append((uid,flags))
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self.connection.executemany('INSERT INTO status (id,flags) VALUES (?,?)',
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data)
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self.connection.commit()
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file.close()
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os.rename(plaintextfilename, plaintextfilename + ".old")
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self.connection.close()
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# Future version upgrades come here...
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# if from_ver <= 1: ... #upgrade from 1 to 2
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# if from_ver <= 2: ... #upgrade from 2 to 3
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@ -98,12 +143,15 @@ class LocalStatusSQLiteFolder(LocalStatusFolder):
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"""Create a new db file"""
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self.ui._msg('Creating new Local Status db for %s:%s' \
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% (self.repository, self))
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connection = sqlite.connect(self.filename)
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cursor = connection.cursor()
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cursor.execute('CREATE TABLE metadata (key VARCHAR(50) PRIMARY KEY, value VARCHAR(128))')
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cursor.execute("INSERT INTO metadata VALUES('db_version', '1')")
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cursor.execute('CREATE TABLE status (id INTEGER PRIMARY KEY, flags VARCHAR(50))')
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self.save() #commit if needed
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if hasattr(self, 'connection'):
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self.connection.close() #close old connections first
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self.connection = sqlite.connect(self.filename, check_same_thread = False)
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self.connection.executescript("""
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CREATE TABLE metadata (key VARCHAR(50) PRIMARY KEY, value VARCHAR(128));
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INSERT INTO metadata VALUES('db_version', '1');
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CREATE TABLE status (id INTEGER PRIMARY KEY, flags VARCHAR(50));
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""")
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self.connection.commit()
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def isnewfolder(self):
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# testing the existence of the db file won't work. It is created
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@ -113,12 +161,12 @@ class LocalStatusSQLiteFolder(LocalStatusFolder):
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def deletemessagelist(self):
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"""delete all messages in the db"""
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self.cursor.execute('DELETE FROM status')
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self.sql_write('DELETE FROM status')
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def cachemessagelist(self):
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self.messagelist = {}
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self.cursor.execute('SELECT id,flags from status')
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for row in self.cursor:
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cursor = self.connection.execute('SELECT id,flags from status')
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for row in cursor:
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flags = [x for x in row[1]]
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self.messagelist[row[0]] = {'uid': row[0], 'flags': flags}
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@ -126,24 +174,41 @@ class LocalStatusSQLiteFolder(LocalStatusFolder):
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#Noop in this backend
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pass
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def uidexists(self,uid):
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self.cursor.execute('SELECT id FROM status WHERE id=:id',{'id': uid})
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for row in self.cursor:
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if(row[0]==uid):
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return 1
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return 0
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def getmessageuidlist(self):
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self.cursor.execute('SELECT id from status')
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r = []
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for row in self.cursor:
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r.append(row[0])
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return r
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def getmessagecount(self):
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self.cursor.execute('SELECT count(id) from status');
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row = self.cursor.fetchone()
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return row[0]
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# Following some pure SQLite functions, where we chose to use
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# BaseFolder() methods instead. Doing those on the in-memory list is
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# quicker anyway. If our db becomes so big that we don't want to
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# maintain the in-memory list anymore, these might come in handy
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# in the future though.
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#
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#def uidexists(self,uid):
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# conn, cursor = self.get_cursor()
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# with conn:
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# cursor.execute('SELECT id FROM status WHERE id=:id',{'id': uid})
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# return cursor.fetchone()
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# This would be the pure SQLite solution, use BaseFolder() method,
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# to avoid threading with sqlite...
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#def getmessageuidlist(self):
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# conn, cursor = self.get_cursor()
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# with conn:
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# cursor.execute('SELECT id from status')
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# r = []
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# for row in cursor:
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# r.append(row[0])
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# return r
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#def getmessagecount(self):
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# conn, cursor = self.get_cursor()
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# with conn:
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# cursor.execute('SELECT count(id) from status');
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# return cursor.fetchone()[0]
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#def getmessageflags(self, uid):
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# conn, cursor = self.get_cursor()
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# with conn:
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# cursor.execute('SELECT flags FROM status WHERE id=:id',
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# {'id': uid})
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# for row in cursor:
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# flags = [x for x in row[0]]
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# return flags
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# assert False,"getmessageflags() called on non-existing message"
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def savemessage(self, uid, content, flags, rtime):
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if uid < 0:
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@ -155,38 +220,23 @@ class LocalStatusSQLiteFolder(LocalStatusFolder):
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return uid
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self.messagelist[uid] = {'uid': uid, 'flags': flags, 'time': rtime}
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flags.sort()
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flags = ''.join(flags)
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self.cursor.execute('INSERT INTO status (id,flags) VALUES (?,?)',
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flags = ''.join(sorted(flags))
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self.sql_write('INSERT INTO status (id,flags) VALUES (?,?)',
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(uid,flags))
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self.save()
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return uid
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def getmessageflags(self, uid):
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self.cursor.execute('SELECT flags FROM status WHERE id=:id',
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{'id': uid})
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for row in self.cursor:
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flags = [x for x in row[0]]
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return flags
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assert False,"getmessageflags() called on non-existing message"
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def getmessagetime(self, uid):
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return self.messagelist[uid]['time']
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def savemessageflags(self, uid, flags):
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self.messagelist[uid] = {'uid': uid, 'flags': flags}
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flags.sort()
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flags = ''.join(flags)
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self.cursor.execute('UPDATE status SET flags=? WHERE id=?',(flags,uid))
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self.save()
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self.sql_write('UPDATE status SET flags=? WHERE id=?',(flags,uid))
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def deletemessages(self, uidlist):
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# Weed out ones not in self.messagelist
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uidlist = [uid for uid in uidlist if uid in self.messagelist]
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if not len(uidlist):
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return
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for uid in uidlist:
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del(self.messagelist[uid])
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#if self.uidexists(uid):
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self.cursor.execute('DELETE FROM status WHERE id=:id', {'id': uid})
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self.sql_write('DELETE FROM status WHERE id=?',
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uidlist)
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