From 7a702edcef2297bd19aef14ef5537a4fd6837607 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Sat, 9 Mar 2019 21:33:16 +0100
Subject: [PATCH] Fix a MIDI-related deadlock in the GUI code.

---
 shared/midi_device.cpp | 6 +++---
 shared/midi_device.h   | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/shared/midi_device.cpp b/shared/midi_device.cpp
index e4b1a11..9d77e21 100644
--- a/shared/midi_device.cpp
+++ b/shared/midi_device.cpp
@@ -73,7 +73,7 @@ void MIDIDevice::thread_func()
 
 	// The sequencer object is now ready to be used from other threads.
 	{
-		lock_guard<mutex> lock(mu);
+		lock_guard<recursive_mutex> lock(mu);
 		alsa_seq = seq;
 		alsa_queue_id = queue_id;
 	}
@@ -97,7 +97,7 @@ void MIDIDevice::thread_func()
 		while (snd_seq_query_next_port(seq, pinfo) >= 0) {
 			constexpr int mask = SND_SEQ_PORT_CAP_READ | SND_SEQ_PORT_CAP_SUBS_READ;
 			if ((snd_seq_port_info_get_capability(pinfo) & mask) == mask) {
-				lock_guard<mutex> lock(mu);
+				lock_guard<recursive_mutex> lock(mu);
 				subscribe_to_port_lock_held(seq, *snd_seq_port_info_get_addr(pinfo));
 			}
 		}
@@ -154,7 +154,7 @@ void MIDIDevice::handle_event(snd_seq_t *seq, snd_seq_event_t *event)
 		return;
 	}
 
-	lock_guard<mutex> lock(mu);
+	lock_guard<recursive_mutex> lock(mu);
 	switch (event->type) {
 	case SND_SEQ_EVENT_CONTROLLER: {
 		receiver->controller_received(event->data.control.param, event->data.control.value);
diff --git a/shared/midi_device.h b/shared/midi_device.h
index a9f33d6..ec6bf9b 100644
--- a/shared/midi_device.h
+++ b/shared/midi_device.h
@@ -47,7 +47,7 @@ public:
 
 	void update_lights(const std::map<LightKey, uint8_t> &active_lights)
 	{
-		std::lock_guard<std::mutex> lock(mu);
+		std::lock_guard<std::recursive_mutex> lock(mu);
 		update_lights_lock_held(active_lights);
 	}
 
@@ -60,7 +60,7 @@ private:
 	std::atomic<bool> should_quit{false};
 	int should_quit_fd;
 
-	mutable std::mutex mu;
+	mutable std::recursive_mutex mu;  // Recursive because the MIDI receiver may update_lights() back while we are sending it stuff.
 	MIDIReceiver *receiver;  // Under <mu>.
 
 	std::thread midi_thread;
-- 
2.39.2