Fix msg pub global lock sharing

Using `None` as the default key for a `@msg.pub` can cause conflicts if
there is more then one "taskless" (no tasks={,} passed) pub offered on
an actor... So instead use the first trio "task name" (usually just the
function name) instead thus avoiding this very hard to debug and
understand problem.

Probably should throw in a test but I'm super lazy today.

tractor/msg.py

@@ -11,7 +11,6 @@ import trio
 import wrapt
 
 from .log import get_logger
-from . import current_actor
 from ._streaming import Context
 
 __all__ = ['pub']
@@ -91,6 +90,7 @@ def modify_subs(topics2ctxs, topics, ctx):
 
 
 _pub_state: Dict[str, dict] = {}
+_pubtask2lock: Dict[str, dict] = {}
 
 
 def pub(
@@ -178,22 +178,22 @@ def pub(
     subscribers. If you are ok to have a new task running for every call
     to ``pub_service()`` then probably don't need this.
     """
-    global _pub_state
+    global _pubtask2lock
 
     # handle the decorator not called with () case
     if wrapped is None:
         return partial(pub, tasks=tasks)
 
-    task2lock: Dict[Union[str, None], trio.StrictFIFOLock] = {
-        None: trio.StrictFIFOLock()}
+    task2lock: Dict[Union[str, None], trio.StrictFIFOLock] = {}
 
     for name in tasks:
         task2lock[name] = trio.StrictFIFOLock()
 
     @wrapt.decorator
     async def wrapper(agen, instance, args, kwargs):
-        # this is used to extract arguments properly as per
-        # the `wrapt` docs
+
+        # XXX: this is used to extract arguments properly as per the
+        # `wrapt` docs
         async def _execute(
             ctx: Context,
             topics: Set[str],
@@ -203,14 +203,22 @@ def pub(
             packetizer: Callable = None,
             **kwargs,
         ):
-            if tasks and task_name is None:
+            if task_name is None:
+                task_name = trio.lowlevel.current_task().name
+
+            if tasks and task_name not in tasks:
                 raise TypeError(
                     f"{agen} must be called with a `task_name` named "
-                    f"argument with a falue from {tasks}")
+                    f"argument with a value from {tasks}")
+
+            elif not tasks and not task2lock:
+                # add a default root-task lock if none defined
+                task2lock[task_name] = trio.StrictFIFOLock()
+
+            _pubtask2lock.update(task2lock)
 
             topics = set(topics)
-            lockmap = _pub_state.setdefault('_pubtask2lock', task2lock)
-            lock = lockmap[task_name]
+            lock = _pubtask2lock[task_name]
 
             all_subs = _pub_state.setdefault('_subs', {})
             topics2ctxs = all_subs.setdefault(task_name, {})