curds: Create a ThreadQueue class

We'll use this for scanning tracks, searching musicbrainz, and fetching
album art. The web services are ratelimited, so it doesn't make sense to
use more than one thread in this case. Additionally, scanning tracks
works best as a single thread since we end up holding a lock the entire
function anyway to prevent duplicates.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

curds/test_threadqueue.py

@@ -0,0 +1,49 @@
+# Copyright 2019 (c) Anna Schumaker.
+import queue
+import unittest
+import threading
+import threadqueue
+
+test_a = 0
+test_b = 0
+test_c = 0
+test_l = threading.Lock()
+
+def set_abc(a, b, c):
+    global test_a, test_b, test_c
+    with test_l:
+        test_a = a
+        test_b = b
+        test_c = c
+
+class TestThreadQueue(unittest.TestCase):
+    def setUp(self):
+        set_abc(0, 0, 0)
+
+    def test_threadqueue_init(self):
+        tq = threadqueue.ThreadQueue()
+        self.assertIsInstance(tq, queue.Queue)
+        self.assertIsInstance(tq, threading.Thread)
+        self.assertIsInstance(tq.stop_event, threading.Event)
+        self.assertTrue(tq.is_alive())
+        tq.stop()
+        self.assertFalse(tq.is_alive())
+
+    def test_threadqueue_push(self):
+        tq = threadqueue.ThreadQueue()
+        with test_l:
+            tq.push(set_abc, 1, 2, 3)
+
+        tq.join()
+        self.assertEqual(test_a, 1)
+        self.assertEqual(test_b, 2)
+        self.assertEqual(test_c, 3)
+
+        for i in range(1000):
+            tq.push(set_abc, i, i+1, i+2)
+
+        tq.join()
+        self.assertEqual(test_a, 999)
+        self.assertEqual(test_b, 1000)
+        self.assertEqual(test_c, 1001)
+        tq.stop()

curds/threadqueue.py

@@ -0,0 +1,26 @@
+# Copyright 2019 (c) Anna Schumaker.
+import queue
+import threading
+
+class ThreadQueue(queue.Queue, threading.Thread):
+    def __init__(self):
+        queue.Queue.__init__(self)
+        threading.Thread.__init__(self)
+        self.stop_event = threading.Event()
+        self.start()
+
+    def push(self, func, *args):
+        self.put((func, args))
+
+    def run(self):
+        while not self.stop_event.is_set():
+            try:
+                (func, args) = self.get(block=True, timeout=0.1)
+                func(*args)
+                self.task_done()
+            except queue.Empty:
+                pass
+
+    def stop(self):
+        self.stop_event.set()
+        threading.Thread.join(self)