added mutex to pdMultiExample for instance func thread safety

pdMultiExample/src/ofApp.cpp

@@ -33,12 +33,16 @@ void ofApp::setup() {
 	ofSoundStreamSetup(numOutputs, numInputs, this, 44100, ofxPd::blockSize()*ticksPerBuffer, 4);
 
 	// allocate pd instance handles
+	instanceMutex.lock();
 	pdinstance1 = pdinstance_new();
 	pdinstance2 = pdinstance_new();
+	instanceMutex.unlock();
 
 	// set a "current" instance before pd.init() or else Pd will make
     // an unnecessary third "default" instance
+	instanceMutex.lock();
 	pd_setinstance(pdinstance1);
+	instanceMutex.unlock();
 
 	// setup Pd
 	//
@@ -65,15 +69,19 @@ void ofApp::setup() {
 	memset(outputBuffer1, 0, bufferSize);
 	memset(outputBuffer2, 0, bufferSize);
 
+	instanceMutex.lock();
 	pd_setinstance(pdinstance1);  // talk to first pd instance
+	instanceMutex.unlock();
 
 	// audio processing on
 	pd.start();
 
 	// open patch
 	pd.openPatch("test.pd");
 
+	instanceMutex.lock();
 	pd_setinstance(pdinstance2); // talk to the second pd instance
+	instanceMutex.unlock();
 
 	// audio processing on
 	pd.start();
@@ -123,7 +131,9 @@ void ofApp::draw() {}
 void ofApp::audioReceived(float * input, int bufferSize, int nChannels) {
 
 	// process audio input for instance 1
+	instanceMutex.lock();
 	pd_setinstance(pdinstance1);
+	instanceMutex.unlock();
 	pd.audioIn(input, bufferSize, nChannels);
 
 	// process audio input for instance 2
@@ -135,11 +145,15 @@ void ofApp::audioReceived(float * input, int bufferSize, int nChannels) {
 void ofApp::audioRequested(float * output, int bufferSize, int nChannels) {
 
 	// process audio output for instance 1
+	instanceMutex.lock();
 	pd_setinstance(pdinstance1);
+	instanceMutex.unlock();
 	pd.audioOut(outputBuffer1, bufferSize, nChannels);
 
 	// process audio output for instance 2
+	instanceMutex.lock();
 	pd_setinstance(pdinstance2);
+	instanceMutex.unlock();
 	pd.audioOut(outputBuffer2, bufferSize, nChannels);
 
 	// mix the two instance output buffers together

pdMultiExample/src/ofApp.h

@@ -58,6 +58,10 @@ class ofApp : public ofBaseApp, public PdReceiver{
 		// pd types which tell libpd to address a separate internal "instance"
 		t_pdinstance *pdinstance1, *pdinstance2;
 
+		// used to avoid concurrency segfaults between main and audio thread
+		// when accessing currently non thread safe pd instance functions
+		ofMutex instanceMutex;
+
 		float* outputBuffer1; //< interleaved audio output buffer for instance 1
 		float* outputBuffer2; //< interleaved audio output buffer for instance 2
 };