Initial webapp design

webapp/job_queue.py

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+
+import json
+import sqlite3
+
+class JobQueue:
+    def __init__(self, dbfile):
+        self.dbfile = dbfile
+        self.db = sqlite3.connect(dbfile, check_same_thread=False)
+        self.db.row_factory = sqlite3.Row
+        with self.db as conn:
+            conn.execute('''CREATE TABLE IF NOT EXISTS jobs
+                    (id INTEGER PRIMARY KEY,
+                    type TEXT,
+                    params TEXT,
+                    client TEXT,
+                    result INTEGER DEFAULT NULL,
+                    created DATETIME DEFAULT CURRENT_TIMESTAMP,
+                    consumed DATETIME DEFAULT NULL,
+                    aborted DATETIME DEFAULT NULL,
+                    finished DATETIME DEFAULT NULL);''')
+    
+    def enqueue(self, task_type:str, client, **params):
+        """ Enqueue a job of the given type with the given params. Returns the new job ID. """
+        with self.db as conn:
+            return conn.execute('INSERT INTO jobs(type, client, params) VALUES (?, ?, ?)',
+                    (task_type, client, json.dumps(params))).lastrowid
+
+    def pop(self, task_type):
+        """ Fetch the next job of the given type. Returns a sqlite3.Row object of the job or None if no jobs of the given
+        type are queued. """
+        with self.db as conn:
+            job = conn.execute('SELECT * FROM jobs WHERE type=? AND consumed IS NULL AND aborted IS NULL ORDER BY created ASC LIMIT 1',
+                    (task_type,)).fetchone()
+            if job is None:
+                return None
+
+            # Atomically commit to this job
+            conn.execute('UPDATE jobs SET consumed=datetime("now") WHERE id=?', (job['id'],))
+
+            return Job(self.db, job)
+
+    def job_iter(self, task_type):
+        return iter(lambda: self.pop(task_type), None)
+
+    def __getitem__(self, key):
+        """ Return the job with the given ID, or raise a KeyError if the key cannot be found. """
+        with self.db as conn:
+            job = conn.execute('SELECT * FROM jobs WHERE id=?', (key,)).fetchone()
+            if job is None:
+                raise KeyError(f'Unknown job ID "{key}"')
+
+            return Job(self.db, job)
+
+class Job(dict):
+    def __init__(self, db, row):
+        super().__init__(json.loads(row['params']))
+        self._db = db
+        self._row = row
+        self.id = row['id']
+        self.type = row['type']
+        self.client = row['client']
+        self.created = row['created']
+        self.consumed = row['consumed']
+        self.finished = row['finished']
+        self.result = row['result']
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, _exc_type, _exc_val, _exc_tb):
+        with self._db as conn:
+            conn.execute('UPDATE jobs SET finished=datetime("now"), result=? WHERE id=?', (self.result, self.id,))
+
+    def abort(self, job_id):
+        with self.db as conn:
+            conn.execute('UPDATE jobs SET aborted=datetime("now") WHERE id=?', (self.id,))
+