SDL: coreaudio: Don't crash on shutdown in a race condition. (d6e93)

SDL Commits
1 
From d6e939ddb50dbe0c5c36ca57f52e2e678678a6d3 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Wed, 28 Sep 2022 09:22:17 -0400
Subject: [PATCH] coreaudio: Don't crash on shutdown in a race condition.

Fixed #6159.
(cherry picked from commit 411582c710097dbc31b7b3e47ab0eb8cc5568b8c)
---
 src/audio/coreaudio/SDL_coreaudio.m | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/audio/coreaudio/SDL_coreaudio.m b/src/audio/coreaudio/SDL_coreaudio.m
index 4d35756579d4..7caa3f479af5 100644
--- a/src/audio/coreaudio/SDL_coreaudio.m
+++ b/src/audio/coreaudio/SDL_coreaudio.m
@@ -523,8 +523,16 @@ static BOOL update_audio_session(_THIS, SDL_bool open, SDL_bool allow_playandrec
 {
     SDL_AudioDevice *this = (SDL_AudioDevice *) inUserData;
 
+    /* This flag is set before this->mixer_lock is destroyed during
+       shutdown, so check it before grabbing the mutex, and then check it
+       again _after_ in case we blocked waiting on the lock. */
+    if (SDL_AtomicGet(&this->shutdown)) {
+        return;  /* don't do anything, since we don't even want to enqueue this buffer again. */
+    }
+
     SDL_LockMutex(this->mixer_lock);
 
+    /* !!! FIXME: why do we have this->hidden->shutdown when this->shutdown exists? */
     if (SDL_AtomicGet(&this->hidden->shutdown)) {
         SDL_UnlockMutex(this->mixer_lock);
         return;  /* don't do anything, since we don't even want to enqueue this buffer again. */