macOS multithreading fix/note

CMakeLists.txt

@@ -205,11 +205,13 @@ if (RTMIDI_BUILD_TESTING)
   add_executable(qmidiin    tests/qmidiin.cpp)
   add_executable(sysextest  tests/sysextest.cpp)
   add_executable(apinames   tests/apinames.cpp)
+  add_executable(backgroundscanner   tests/backgroundscanner.cpp)
   list(GET LIB_TARGETS 0 LIBRTMIDI)
-  set_target_properties(cmidiin midiclock midiout midiprobe qmidiin sysextest apinames
+  set_target_properties(cmidiin midiclock midiout midiprobe qmidiin sysextest apinames backgroundscanner
     PROPERTIES RUNTIME_OUTPUT_DIRECTORY tests
                INCLUDE_DIRECTORIES ${CMAKE_CURRENT_SOURCE_DIR}
                LINK_LIBRARIES ${LIBRTMIDI})
+  target_compile_options(backgroundscanner PUBLIC "-std=c++11")
   add_test(NAME apinames COMMAND apinames)
 endif()
 

README.md

@@ -30,6 +30,10 @@ MIDI input and output functionality are separated into two classes, `RtMidiIn` a
 
 In some cases, for example to use RtMidi with GS Synth, it may be necessary for your program to call `CoInitializeEx` and `CoUninitialize` on entry to and exit from the thread that uses RtMidi.
 
+## OSX / macOS
+
+- In *multithreaded* setups port enumeration might not properly update which is due to the macOS system processing loops not being called. To resolve make sure to call `RtMidi_multithreadRunLoop()` (declared only when `__APPLE__` is defined which should be automatically) in relevant threads (other threads (the first thread) in which RtMidi objects have been instantiated). Also see example `tests/backgroundscanner.cpp`.
+
 ## Further reading
 
 For complete documentation on RtMidi, see the `doc` directory of the distribution or surf to http://www.music.mcgill.ca/~gary/rtmidi/.

RtMidi.cpp

@@ -732,6 +732,10 @@ struct CoreMidiData {
   MIDISysexSendRequest sysexreq;
 };
 
+void RtMidi_multithreadRunLoop(){
+  CFRunLoopRunInMode( kCFRunLoopDefaultMode, 0, false );
+}
+
 //*********************************************************************//
 //  API: OS-X
 //  Class Definitions: MidiInCore

RtMidi.h

@@ -626,4 +626,10 @@ inline void RtMidiOut :: sendMessage( const std::vector<unsigned char> *message
 inline void RtMidiOut :: sendMessage( const unsigned char *message, size_t size ) { static_cast<MidiOutApi *>(rtapi_)->sendMessage( message, size ); }
 inline void RtMidiOut :: setErrorCallback( RtMidiErrorCallback errorCallback, void *userData ) { rtapi_->setErrorCallback(errorCallback, userData); }
 
+#if defined(__APPLE__)
+
+void RtMidi_multithreadRunLoop();
+
+#endif /* __MACOSX_CORE__ */
+
 #endif

tests/backgroundscanner.cpp

@@ -0,0 +1,59 @@
+#include <iostream>
+#include <chrono>
+#include <thread>
+#include <ctime>
+
+#include "RtMidi.h"
+
+
+int main(int argc, char * argv[]){
+
+  const unsigned int interval = 1000;
+  unsigned int round = 0;
+
+  RtMidiIn * baseThreadPort = new RtMidiIn();
+
+  baseThreadPort->openVirtualPort("baseThreadPort");
+
+  std::thread thr = std::thread([interval, &round]() {
+
+    for(round = 1;; round++){
+
+      RtMidiIn * midi = NULL;
+
+      try {
+        midi = new RtMidiIn();
+
+        unsigned int nPorts = midi->getPortCount();
+
+        std::cout << "Scan-Round " << std::to_string(round) << ", found " << nPorts << " ports" << std::endl;
+
+        for ( unsigned int i=0; i<nPorts; i++ ) {
+
+          std::string name = midi->getPortName(i);
+
+          std::cout << "\t #" << i << " " << name << std::endl;
+        }
+
+      } catch ( RtMidiError &error ) {
+        error.printMessage();
+      }
+
+      delete midi;
+
+      std::this_thread::sleep_for(std::chrono::milliseconds(interval));
+    }
+  });
+
+  // loop until CTRL-C
+  std::cout << ">>>>>>>>> PRESS CTRL-C to QUIT <<<<<<<<<<" << std::endl;
+  while(1){
+
+    #ifdef __APPLE__
+    RtMidi_multithreadRunLoop();
+    #endif
+
+  }
+
+  return EXIT_SUCCESS;
+}