Hold the symbol_get_event in the entire body of create_symbol_embed

While the previous code was safe, the synchronization was spread out
over different modules and was hard to wrap around. Additionally changes
could introduce context switches without the author being aware of them
causing potential race conditions with the refresh.
Moving the whole body into the with block solves both of these issues

1 files changed, 24 insertions, 24 deletions

diff --git a/bot/exts/info/doc/_cog.py b/bot/exts/info/doc/_cog.py
index fb45d0bbb..24b571ddb 100644
--- a/bot/exts/info/doc/_cog.py
+++ b/bot/exts/info/doc/_cog.py
@@ -251,8 +251,7 @@ class DocCog(commands.Cog):
         First a redis lookup is attempted, if that fails the `item_fetcher`
         is used to fetch the page and parse the HTML from it into Markdown.
         """
-        with self.symbol_get_event:
-            markdown = await doc_cache.get(doc_item)
+        markdown = await doc_cache.get(doc_item)
 
         if markdown is None:
             log.debug(f"Redis cache miss with {doc_item}.")
@@ -283,29 +282,30 @@ class DocCog(commands.Cog):
         if not self.refresh_event.is_set():
             log.debug("Waiting for inventories to be refreshed before processing item.")
             await self.refresh_event.wait()
+        # Ensure a refresh can't run in case of a context switch until the with block is exited
+        with self.symbol_get_event:
+            doc_item = self.get_symbol_item(symbol_name)
+            if doc_item is None:
+                log.debug("Symbol does not exist.")
+                return None
+
+            self.bot.stats.incr(f"doc_fetches.{doc_item.package}")
+
+            # Show all symbols with the same name that were renamed in the footer,
+            # with a max of 100 chars.
+            if symbol_name in self.renamed_symbols:
+                renamed_symbols = ', '.join(self.renamed_symbols[symbol_name])
+                footer_text = textwrap.shorten("Moved: " + renamed_symbols, 100, placeholder=' ...')
+            else:
+                footer_text = ""
 
-        doc_item = self.get_symbol_item(symbol_name)
-        if doc_item is None:
-            log.debug("Symbol does not exist.")
-            return None
-
-        self.bot.stats.incr(f"doc_fetches.{doc_item.package}")
-
-        # Show all symbols with the same name that were renamed in the footer,
-        # with a max of 100 chars.
-        if symbol_name in self.renamed_symbols:
-            renamed_symbols = ', '.join(self.renamed_symbols[symbol_name])
-            footer_text = textwrap.shorten("Moved: " + renamed_symbols, 100, placeholder=' ...')
-        else:
-            footer_text = ""
-
-        embed = discord.Embed(
-            title=discord.utils.escape_markdown(symbol_name),
-            url=f"{doc_item.url}#{doc_item.symbol_id}",
-            description=await self.get_symbol_markdown(doc_item)
-        )
-        embed.set_footer(text=footer_text)
-        return embed
+            embed = discord.Embed(
+                title=discord.utils.escape_markdown(symbol_name),
+                url=f"{doc_item.url}#{doc_item.symbol_id}",
+                description=await self.get_symbol_markdown(doc_item)
+            )
+            embed.set_footer(text=footer_text)
+            return embed
 
     @commands.group(name='docs', aliases=('doc', 'd'), invoke_without_command=True)
     async def docs_group(self, ctx: commands.Context, *, symbol_name: Optional[str]) -> None: