From 5c138561bb08dffd3353c97c8720b4123e524f8a Mon Sep 17 00:00:00 2001
From: reuk <reuk@users.noreply.github.com>
Date: Mon, 2 Dec 2024 19:14:15 +0000
Subject: [PATCH] MidiDeviceListConnectionBroadcaster: Avoid constructing
 MessageManager on incorrect thread

Previously, if the very first call to
MidiDeviceListConnectionBroadcaster::get() happened on a background
thread (which could happen on macOS in response to a MIDI setup
configuration change), then MessageManager::getInstance and
getAvailableDevices could be called on that same thread.

With this change in place, midi change notifications will be ignored if
there's no message manager available, and getAvailableDevices will only
be called on the message thread.
---
 ...ce_MidiDeviceListConnectionBroadcaster.cpp | 22 ++++++++++---------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/modules/juce_audio_devices/midi_io/juce_MidiDeviceListConnectionBroadcaster.cpp b/modules/juce_audio_devices/midi_io/juce_MidiDeviceListConnectionBroadcaster.cpp
index 89e843d765..c80d2168de 100644
--- a/modules/juce_audio_devices/midi_io/juce_MidiDeviceListConnectionBroadcaster.cpp
+++ b/modules/juce_audio_devices/midi_io/juce_MidiDeviceListConnectionBroadcaster.cpp
@@ -57,20 +57,22 @@ public:
 
     void notify()
     {
-        if (MessageManager::getInstance()->isThisTheMessageThread())
-        {
-            cancelPendingUpdate();
+        auto* mm = MessageManager::getInstanceWithoutCreating();
 
-            const State newState;
+        if (mm == nullptr)
+            return;
 
-            if (std::exchange (lastNotifiedState, newState) != newState)
-                for (auto it = callbacks.begin(); it != callbacks.end();)
-                    NullCheckedInvocation::invoke ((it++)->second);
-        }
-        else
+        if (! mm->isThisTheMessageThread())
         {
             triggerAsyncUpdate();
+            return;
         }
+
+        cancelPendingUpdate();
+
+        if (auto prev = std::exchange (lastNotifiedState, State{}); prev != lastNotifiedState)
+            for (auto it = callbacks.begin(); it != callbacks.end();)
+                NullCheckedInvocation::invoke ((it++)->second);
     }
 
     static auto& get()
@@ -108,7 +110,7 @@ private:
     }
 
     std::map<MidiDeviceListConnection::Key, std::function<void()>> callbacks;
-    State lastNotifiedState;
+    std::optional<State> lastNotifiedState;
     MidiDeviceListConnection::Key key = 0;
 };