From b1250515e7d6d3545bcfd850c6286c69239cb420 Mon Sep 17 00:00:00 2001
From: Numerlor <25886452+Numerlor@users.noreply.github.com>
Date: Thu, 14 Jan 2021 05:17:07 +0100
Subject: Prevent an inventory refresh while waiting for item cache

If an inventory refresh was started while the symbol embed coroutine
was suspended, it could cause the parser to try to fetch a non existent
future if the markdown was requested after it was cleared but before
new inventories were loaded in.
---
 bot/exts/info/doc/_cog.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/bot/exts/info/doc/_cog.py b/bot/exts/info/doc/_cog.py
index 942d685af..7b9dad135 100644
--- a/bot/exts/info/doc/_cog.py
+++ b/bot/exts/info/doc/_cog.py
@@ -70,6 +70,9 @@ class DocCog(commands.Cog):
 
         self.refresh_event = asyncio.Event()
         self.refresh_event.set()
+        self.symbol_get_event = asyncio.Event()
+        self.symbol_get_event.set()
+
         self.init_refresh_task = self.bot.loop.create_task(self.init_refresh_inventory())
 
     @lock("doc", COMMAND_LOCK_SINGLETON, raise_error=True)
@@ -206,6 +209,7 @@ class DocCog(commands.Cog):
     async def refresh_inventory(self) -> None:
         """Refresh internal documentation inventory."""
         self.refresh_event.clear()
+        await self.symbol_get_event.wait()
         log.debug("Refreshing documentation inventory...")
         self.inventory_scheduler.cancel_all()
         self.inventory_reschedule_attempts.clear()
@@ -248,7 +252,10 @@ class DocCog(commands.Cog):
             return None
         self.bot.stats.incr(f"doc_fetches.{symbol_info.package}")
 
+        self.symbol_get_event.clear()
         markdown = await doc_cache.get(symbol_info)
+        self.symbol_get_event.set()
+
         if markdown is None:
             log.debug(f"Redis cache miss for symbol `{symbol}`.")
             markdown = await self.item_fetcher.get_markdown(symbol_info)
-- 
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