fix concurrency issue by serializing role transfers

src/esoserver.py

@@ -2,22 +2,28 @@ import util
 import random
 import logging
 import discord
+import asyncio
 
 import metrics
 
+role_transfer_lock = asyncio.Lock()
+
 def setup(bot):
 	@bot.listen()
 	async def on_message(message):
 		if message.guild.id == util.config["esoserver"]["id"]:
-			for role in message.role_mentions:
-				if role.id == util.config["esoserver"]["transfer_role"]: # transfer the role from sender to other pinged person
-					if len(message.mentions) == 1:
-						await message.author.remove_roles(role, reason="untransfer unrole")
-						await message.mentions[0].add_roles(role, reason="transfer role")
-					return
-			for user in message.mentions:
-				for role in user.roles:
-					if role.id == util.config["esoserver"]["transfer_role"]: # transfer from pingee to pinger
-						await user.remove_roles(role, reason="untransfer unrole")
-						await message.author.add_roles(role, reason="transfer role")
-						return
+			async with role_transfer_lock: # prevent concurrency horrors - serialize accesses, probably
+				for role in message.role_mentions:
+					if role.id == util.config["esoserver"]["transfer_role"]: # transfer the role from sender to other pinged person
+						if len(message.mentions) == 1:
+							await message.author.remove_roles(role, reason="untransfer unrole")
+							await message.mentions[0].add_roles(role, reason="transfer role")
+							metrics.role_transfers.inc()
+						return
+				for user in message.mentions:
+					for role in user.roles:
+						if role.id == util.config["esoserver"]["transfer_role"]: # transfer from pingee to pinger
+							await user.remove_roles(role, reason="untransfer unrole")
+							await message.author.add_roles(role, reason="transfer role")
+							metrics.role_transfers.inc()
+							return

src/metrics.py

@@ -2,3 +2,4 @@ import prometheus_client
 
 achievements_achieved = prometheus_client.Counter("abr_achievements", "Achievements achieved by users")
 reminders_fired = prometheus_client.Counter("abr_reminders", "Reminders successfully delivered to users")
+role_transfers = prometheus_client.Counter("abr_role_transfers", "Times the esoserver transferable role has been transferred")