lib: Add locking around TagStore add() and remove()

But make sure we don't call the publishers while holding the lock to
avoid deadlocks.

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

lib/tagstore.py

@@ -1,19 +1,26 @@
 # Copyright 2021 (c) Anna Schumaker.
 from . import publisher
 from . import tag
+import threading
 
 class TagStore:
     def __init__(self):
         self.store = dict()
+        self.lock = threading.Lock()
         self.Added = publisher.Publisher()
         self.Removed = publisher.Publisher()
 
-    def add(self, name, track=None):
-        name = name.strip()
-        if (t := self.store.get(name)) == None:
+    def __get_tag__(self, name):
+        with self.lock:
+            if (t := self.store.get(name)) != None:
+                return t
             t = tag.Tag(name)
             self.store[name] = t
-            self.Added.publish(t)
+        self.Added.publish(t)
+        return t
+
+    def add(self, name, track=None):
+        t = self.__get_tag__(name.strip())
         if track:
             t.add_track(track)
         return t
@@ -21,6 +28,7 @@ class TagStore:
     def remove(self, t, track=None):
         if track:
             t.remove_track(track)
-        if (track==None or len(t) == 0) and t in self.store.values():
-            self.store.pop(t.name)
+        if (track == None or len(t) == 0) and t in self.store.values():
+            with self.lock:
+                self.store.pop(t.name)
             self.Removed.publish(t)

lib/test_tagstore.py

@@ -1,6 +1,7 @@
 # Copyright 2021 (c) Anna Schumaker.
 from . import publisher
 from . import tagstore
+import threading
 import unittest
 
 class TestTagStore(unittest.TestCase):
@@ -17,6 +18,7 @@ class TestTagStore(unittest.TestCase):
     def test_tag_store(self):
         store = tagstore.TagStore()
         self.assertEqual(store.store, { })
+        self.assertIsInstance(store.lock, type(threading.Lock()))
         self.assertIsInstance(store.Added, publisher.Publisher)
         self.assertIsInstance(store.Removed, publisher.Publisher)