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"]:
+			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")