Created
November 11, 2017 09:14
-
-
Save cessor/f8bf530212fbe75263c79564f5fc15ad to your computer and use it in GitHub Desktop.
Multiprocessing & Sqlite Example
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| import sqlite3 | |
| import multiprocessing | |
| ''' | |
| This program starts a daemon process that listens on a queue. | |
| It then starts 10 processes that place integers in the queue. | |
| The listening daemon pulls the integers out of the queue and | |
| stores them in the database. | |
| ''' | |
| DB_FILENAME = 'db.sqlite' | |
| class DbCommands(object): | |
| CLEAR = 'delete from test' | |
| DROP = 'drop table if exists test' | |
| COUNT = 'select count(*) from test' | |
| INIT = 'create table if not exists test (value integer not null)' | |
| INSERT = 'insert into test (value) values (?)' | |
| class Database(object): | |
| def __init__(self, path): | |
| self._path = path | |
| self._connection = None | |
| def __enter__(self): | |
| self._connection = sqlite3.connect(self._path) | |
| # Reset Database | |
| self.execute(DbCommands.DROP) | |
| self.execute(DbCommands.INIT) | |
| self.execute(DbCommands.CLEAR) | |
| return self | |
| def __exit__(self, *args, **kwargs): | |
| self._connection.commit() | |
| def commit(self): | |
| self._connection.commit() | |
| def execute(self, sql, *args): | |
| cursor = self._connection.cursor() | |
| if not args: | |
| return cursor.execute(sql) | |
| return cursor.execute(sql, args) | |
| class Command(object): | |
| def __init__(self, *args): | |
| self._args = args | |
| class Count(Command): | |
| def execute(self, database): | |
| count = database.execute(DbCommands.COUNT).fetchall() | |
| count = count[0][0] | |
| print('Count: ', count) | |
| class Commit(Command): | |
| def execute(self, database): | |
| database.commit() | |
| raise Break() | |
| class Insert(Command): | |
| def execute(self, database): | |
| database.execute(DbCommands.INSERT, *self._args) | |
| class Break(Exception): | |
| pass | |
| def handle(queue): | |
| with Database(DB_FILENAME) as database: | |
| while True: | |
| try: | |
| command = queue.get() | |
| command.execute(database) | |
| queue.task_done() | |
| except Break: | |
| queue.task_done() | |
| break | |
| except Exception as e: | |
| print(e) | |
| def add_to_queue(queue): | |
| for i in range(100): | |
| queue.put(Insert(i)) | |
| def main(): | |
| queue = multiprocessing.JoinableQueue() | |
| # Start a Daemon Process | |
| multiprocessing.Process(target=handle, args=(queue,), daemon=True).start() | |
| # Start Processes | |
| processes = [ | |
| multiprocessing.Process(target=add_to_queue, args=(queue,)) | |
| for _ in range(10) | |
| ] | |
| # Start Daemons | |
| for process in processes: | |
| process.start() | |
| # Wait until Daemons are done | |
| for process in processes: | |
| process.join() | |
| # Query a command to the database | |
| queue.put(Count()) | |
| # Send a command to the handler | |
| # To commit, clean, and close the database | |
| queue.put(Commit()) | |
| # Do Not Join Daemon Threads, | |
| # Join their Queues instead | |
| queue.join() | |
| if __name__ == '__main__': | |
| main() |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment