diff -r 87dfa7c89294 -r ee976a1d1f0a AlsaBridge.cpp
--- a/AlsaBridge.cpp	Sun Dec 20 01:56:47 2020 +0100
+++ b/AlsaBridge.cpp	Mon Dec 21 16:44:39 2020 +0100
@@ -17,6 +17,7 @@
 #include <iostream>
 #include <stdexcept>
 #include <thread>
+#include <mutex>
 #include <atomic>
 
 #include <alsa/asoundlib.h>
@@ -32,18 +33,21 @@
 	snd_rawmidi_t* input;
 	snd_rawmidi_t* output;
 	std::thread receivingThread;
+	std::recursive_mutex midiMutex;
 	std::atomic<bool> stopped{false};
 
 	void run() {
 		while (!stopped) {
-			// TODO: poll
-			uint8_t buffer[256];
-			ssize_t length = snd_rawmidi_read(input, buffer, sizeof (buffer));
-			if (length > 0 && length <= sizeof (buffer)) {
-				// TODO: multiple messages combined together?
-				djmFix->receive(MidiMessage(buffer, buffer + length));
+			{
+				std::lock_guard<std::recursive_mutex> lock(midiMutex);
+				// TODO: poll
+				uint8_t buffer[256];
+				ssize_t length = snd_rawmidi_read(input, buffer, sizeof (buffer));
+				if (length > 0 && length <= sizeof (buffer)) {
+					// TODO: multiple messages combined together?
+					djmFix->receive(MidiMessage(buffer, buffer + length));
+				}
 			}
-
 			std::this_thread::sleep_for(std::chrono::milliseconds(100));
 		}
 	}
@@ -78,6 +82,7 @@
 	}
 
 	virtual void send(MidiMessage midiMessage) override {
+		std::lock_guard<std::recursive_mutex> lock(midiMutex);
 		ssize_t length = snd_rawmidi_write(output, midiMessage.data(), midiMessage.size());
 		std::cerr << "AlsaBridgeImpl::send(): length = " << length << std::endl; // TODO: do not mess STDIO
 	}