Config locks (#2654)

* Config locks

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Add locks for all_XXX

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Remove a word

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Add acquire_lock kwarg for value context manager

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Add towncrier entry

Signed-off-by: Toby <tobyharradine@gmail.com>

* Fix issues with `get_custom_lock` and `get_members_lock`

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

tests/core/test_config.py

@@ -1,3 +1,4 @@
+import asyncio
 from unittest.mock import patch
 import pytest
 
@@ -506,3 +507,50 @@ def test_config_custom_doubleinit(config):
     config.init_custom("TEST", 3)
     with pytest.raises(ValueError):
         config.init_custom("TEST", 2)
+
+
+@pytest.mark.asyncio
+async def test_config_locks_cache(config, empty_guild):
+    lock1 = config.foo.get_lock()
+    assert lock1 is config.foo.get_lock()
+    lock2 = config.guild(empty_guild).foo.get_lock()
+    assert lock2 is config.guild(empty_guild).foo.get_lock()
+    assert lock1 is not lock2
+
+
+@pytest.mark.asyncio
+async def test_config_value_atomicity(config):
+    config.register_global(foo=[])
+    tasks = []
+    for _ in range(15):
+
+        async def func():
+            async with config.foo.get_lock():
+                foo = await config.foo()
+                foo.append(0)
+                await asyncio.sleep(0.1)
+                await config.foo.set(foo)
+
+        tasks.append(func())
+
+    await asyncio.wait(tasks, return_when=asyncio.ALL_COMPLETED)
+
+    assert len(await config.foo()) == 15
+
+
+@pytest.mark.asyncio
+async def test_config_ctxmgr_atomicity(config):
+    config.register_global(foo=[])
+    tasks = []
+    for _ in range(15):
+
+        async def func():
+            async with config.foo() as foo:
+                foo.append(0)
+                await asyncio.sleep(0.1)
+
+        tasks.append(func())
+
+    await asyncio.wait(tasks, return_when=asyncio.ALL_COMPLETED)
+
+    assert len(await config.foo()) == 15