Avoid during-iteration scheduler plugin changes (#5259)

distributed/scheduler.py

@@ -2245,7 +2245,7 @@ def _transition(self, key, finish: str, *args, **kwargs):
                     ts._dependents = dependents
                     ts._dependencies = dependencies
                     parent._tasks[ts._key] = ts
-                for plugin in self.plugins.values():
+                for plugin in list(self.plugins.values()):
                     try:
                         plugin.transition(key, start, finish2, *args, **kwargs)
                     except Exception:
@@ -3949,7 +3949,9 @@ def del_scheduler_file():
         for preload in self.preloads:
             await preload.start()
 
-        await asyncio.gather(*[plugin.start(self) for plugin in self.plugins.values()])
+        await asyncio.gather(
+            *[plugin.start(self) for plugin in list(self.plugins.values())]
+        )
 
         self.start_periodic_callbacks()
 
@@ -3988,7 +3990,9 @@ async def close(self, comm=None, fast=False, close_workers=False):
                 else:
                     break
 
-        await asyncio.gather(*[plugin.close() for plugin in self.plugins.values()])
+        await asyncio.gather(
+            *[plugin.close() for plugin in list(self.plugins.values())]
+        )
 
         for pc in self.periodic_callbacks.values():
             pc.stop()
@@ -4239,7 +4243,7 @@ async def add_worker(
             if ws._nthreads > len(ws._processing):
                 parent._idle[ws._address] = ws
 
-            for plugin in self.plugins.values():
+            for plugin in list(self.plugins.values()):
                 try:
                     result = plugin.add_worker(scheduler=self, worker=address)
                     if inspect.isawaitable(result):
@@ -4653,7 +4657,7 @@ def update_graph(
                     recommendations[ts._key] = "erred"
                     break
 
-        for plugin in self.plugins.values():
+        for plugin in list(self.plugins.values()):
             try:
                 plugin.update_graph(
                     self,
@@ -4916,7 +4920,7 @@ async def remove_worker(self, comm=None, address=None, safe=False, close=True):
 
             self.transitions(recommendations)
 
-            for plugin in self.plugins.values():
+            for plugin in list(self.plugins.values()):
                 try:
                     result = plugin.remove_worker(scheduler=self, worker=address)
                     if inspect.isawaitable(result):
@@ -5219,7 +5223,7 @@ async def add_client(self, comm, client=None, versions=None):
         self.log_event(["all", client], {"action": "add-client", "client": client})
         parent._clients[client] = ClientState(client, versions=versions)
 
-        for plugin in self.plugins.values():
+        for plugin in list(self.plugins.values()):
             try:
                 plugin.add_client(scheduler=self, client=client)
             except Exception as e:
@@ -5274,7 +5278,7 @@ def remove_client(self, client=None):
             )
             del parent._clients[client]
 
-            for plugin in self.plugins.values():
+            for plugin in list(self.plugins.values()):
                 try:
                     plugin.remove_client(scheduler=self, client=client)
                 except Exception as e:
@@ -5511,8 +5515,8 @@ def remove_plugin(self, plugin=None, name=None):
             self.plugins.pop(plugin.name)
         else:
             # TODO: Remove this block of code once removing plugins by value is disabled
-            if plugin in self.plugins.values():
-                if sum(plugin is p for p in self.plugins.values()) > 1:
+            if plugin in list(self.plugins.values()):
+                if sum(plugin is p for p in list(self.plugins.values())) > 1:
                     raise ValueError(
                         f"Multiple instances of {plugin} were found in the current scheduler "
                         "plugins, we cannot remove this plugin."
@@ -5755,7 +5759,7 @@ async def restart(self, client=None, timeout=30):
 
             self.clear_task_state()
 
-            for plugin in self.plugins.values():
+            for plugin in list(self.plugins.values()):
                 try:
                     plugin.restart(self)
                 except Exception as e:
@@ -7023,7 +7027,7 @@ def start_task_metadata(self, comm=None, name=None):
     def stop_task_metadata(self, comm=None, name=None):
         plugins = [
             p
-            for p in self.plugins.values()
+            for p in list(self.plugins.values())
             if isinstance(p, CollectTaskMetaDataPlugin) and p.name == name
         ]
         if len(plugins) != 1: