diff --git a/src/AppFrame.cpp b/src/AppFrame.cpp
index ca5a8c1..6abd434 100644
--- a/src/AppFrame.cpp
+++ b/src/AppFrame.cpp
@@ -1612,6 +1612,9 @@ void AppFrame::OnIdle(wxIdleEvent& event) {
         updateDeviceParams();
     }
     
+    //try to garbage collect the retired demodulators.
+    wxGetApp().getDemodMgr().garbageCollect();
+
     DemodulatorInstance *demod = wxGetApp().getDemodMgr().getLastActiveDemodulator();
 
     if (demod && demod->isModemInitialized()) {
diff --git a/src/demod/DemodulatorInstance.cpp b/src/demod/DemodulatorInstance.cpp
index 355daa6..9605707 100644
--- a/src/demod/DemodulatorInstance.cpp
+++ b/src/demod/DemodulatorInstance.cpp
@@ -78,6 +78,7 @@ DemodulatorInstance::DemodulatorInstance() {
 }
 
 DemodulatorInstance::~DemodulatorInstance() {
+    std::lock_guard < std::mutex > lockData(m_thread_control_mutex);
 #if ENABLE_DIGITAL_LAB
     delete activeOutput;
 #endif
@@ -89,7 +90,7 @@ DemodulatorInstance::~DemodulatorInstance() {
     delete threadQueueControl;
     delete pipeAudioData;
     
-    wxGetApp().getBookmarkMgr().updateActiveList();
+   // wxGetApp().getBookmarkMgr().updateActiveList();
 }
 
 void DemodulatorInstance::setVisualOutputQueue(DemodulatorThreadOutputQueue *tQueue) {
@@ -97,6 +98,9 @@ void DemodulatorInstance::setVisualOutputQueue(DemodulatorThreadOutputQueue *tQu
 }
 
 void DemodulatorInstance::run() {
+
+    std::lock_guard < std::mutex > lockData(m_thread_control_mutex);
+
     if (active) {
         return;
     }
@@ -128,7 +132,7 @@ void DemodulatorInstance::run() {
 
     active = true;
 
-    wxGetApp().getBookmarkMgr().updateActiveList();
+ //   wxGetApp().getBookmarkMgr().updateActiveList();
 }
 
 void DemodulatorInstance::updateLabel(long long freq) {
@@ -166,7 +170,8 @@ void DemodulatorInstance::setLabel(std::string labelStr) {
 
 bool DemodulatorInstance::isTerminated() {
 
-    //
+    std::lock_guard < std::mutex > lockData(m_thread_control_mutex);
+
     bool audioTerminated = audioThread->isTerminated();
     bool demodTerminated = demodulatorThread->isTerminated();
     bool preDemodTerminated = demodulatorPreThread->isTerminated();
diff --git a/src/demod/DemodulatorInstance.h b/src/demod/DemodulatorInstance.h
index 749c6ec..a5be9d1 100644
--- a/src/demod/DemodulatorInstance.h
+++ b/src/demod/DemodulatorInstance.h
@@ -130,7 +130,7 @@ public:
     void closeOutput();
 #endif
         
-protected:
+private:
     DemodulatorThreadInputQueue* pipeIQInputData;
     DemodulatorThreadPostInputQueue* pipeIQDemodData;
     AudioThreadInputQueue *pipeAudioData;
@@ -138,7 +138,8 @@ protected:
     DemodulatorThread *demodulatorThread;
     DemodulatorThreadControlCommandQueue *threadQueueControl;
 
-private:
+    //protects child thread creation and termination 
+    mutable std::mutex m_thread_control_mutex;
 
     std::atomic<std::string *> label; //
     // User editable buffer, 16 bit string.
diff --git a/src/demod/DemodulatorMgr.cpp b/src/demod/DemodulatorMgr.cpp
index c0a582d..761a6b6 100644
--- a/src/demod/DemodulatorMgr.cpp
+++ b/src/demod/DemodulatorMgr.cpp
@@ -163,6 +163,7 @@ void DemodulatorMgr::deleteThread(DemodulatorInstance *demod) {
     demod->terminate();
 
     //Do not cleanup immediatly
+    std::lock_guard < std::mutex > lock_deleted(deleted_demods_busy);
     demods_deleted.push_back(demod);
 }
 
@@ -225,10 +226,7 @@ void DemodulatorMgr::setActiveDemodulator(DemodulatorInstance *demod, bool tempo
         }
 #endif
         wxGetApp().getBookmarkMgr().updateActiveList();
-    } else {
-        std::lock_guard < std::recursive_mutex > lock(demods_busy);
-        garbageCollect();
-    }
+    } 
 
     if (activeVisualDemodulator.load()) {
         activeVisualDemodulator.load()->setVisualOutputQueue(nullptr);
@@ -280,8 +278,9 @@ DemodulatorInstance *DemodulatorMgr::getLastDemodulatorWith(const std::string& t
 	return nullptr;
 }
 
-//Private internal method, no need to protect it with demods_busy
 void DemodulatorMgr::garbageCollect() {
+    
+    std::lock_guard < std::mutex > lock(deleted_demods_busy);
 
     std::vector<DemodulatorInstance *>::iterator it = demods_deleted.begin();
 
@@ -290,11 +289,13 @@ void DemodulatorMgr::garbageCollect() {
         if ((*it)->isTerminated()) {
            
             DemodulatorInstance *deleted = (*it);
+      
+            std::cout << "Garbage collected demodulator instance '" << deleted->getLabel() << "'... " << std::endl << std::flush;
+            demods_deleted.erase(it);
             delete deleted;
 
-            it = demods_deleted.erase(it);
-
-            std::cout << "Garbage collected demodulator instance '" << deleted->getLabel() << "'... " << std::endl << std::flush;
+            //only garbage collect 1 demod at a time.
+            return;
         }
         else {
             it++;
@@ -431,7 +432,6 @@ void DemodulatorMgr::saveInstance(DataNode *node, DemodulatorInstance *inst) {
             *settingsNode->newChild(msi->first.c_str()) = msi->second;
         }
     }
-
 }
 
 DemodulatorInstance *DemodulatorMgr::loadInstance(DataNode *node) {
diff --git a/src/demod/DemodulatorMgr.h b/src/demod/DemodulatorMgr.h
index ca65c22..e6887f1 100644
--- a/src/demod/DemodulatorMgr.h
+++ b/src/demod/DemodulatorMgr.h
@@ -67,10 +67,11 @@ public:
     void saveInstance(DataNode *node, DemodulatorInstance *inst);
 	
     DemodulatorInstance *loadInstance(DataNode *node);
+
+    //to be called periodically to cleanup removed demodulators.
+    void garbageCollect();
     
 private:
-    
-    void garbageCollect();
 
     std::vector<DemodulatorInstance *> demods;
     std::vector<DemodulatorInstance *> demods_deleted;
@@ -91,6 +92,8 @@ private:
     //protects access to demods lists and such, need to be recursive
     //because of the usage of public re-entrant methods 
     std::recursive_mutex demods_busy;
+
+    mutable std::mutex deleted_demods_busy;
     
     std::map<std::string, ModemSettings> lastModemSettings;
     std::map<int,RtAudio::DeviceInfo> outputDevices;
diff --git a/src/process/VisualProcessor.h b/src/process/VisualProcessor.h
index 7d8110c..c7f77be 100644
--- a/src/process/VisualProcessor.h
+++ b/src/process/VisualProcessor.h
@@ -170,7 +170,7 @@ protected:
             if (inp) {
                 OutputDataTypePtr outp = buffers.getBuffer();
 
-                //'deep copy of the contents 
+                //'deep copy' of the contents 
                 (*outp) = (*inp);
   
                 VisualProcessor<OutputDataType, OutputDataType>::distribute(outp);
diff --git a/src/sdr/SDRPostThread.cpp b/src/sdr/SDRPostThread.cpp
index db82fd7..01298e2 100644
--- a/src/sdr/SDRPostThread.cpp
+++ b/src/sdr/SDRPostThread.cpp
@@ -221,8 +221,8 @@ void SDRPostThread::run() {
         iqVisualQueue->flush();   
     }
 
-   buffers.purge();
-   visualDataBuffers.purge();
+    //    buffers.purge();
+    //    visualDataBuffers.purge();
 
 //    std::cout << "SDR post-processing thread done." << std::endl;
 }
diff --git a/src/util/ThreadBlockingQueue.h b/src/util/ThreadBlockingQueue.h
index 47819d0..d4b7c1e 100644
--- a/src/util/ThreadBlockingQueue.h
+++ b/src/util/ThreadBlockingQueue.h
@@ -36,7 +36,7 @@ public:
 
     /*! Create safe blocking queue. */
     ThreadBlockingQueue() {
-        //at least 1 (== Exchanger)
+        //at least 1 (== Java SynchronizedQueue)
         m_max_num_items = MIN_ITEM_NB;
     };
     
@@ -258,7 +258,7 @@ public:
     }
 
 private:
-    //TODO: use a circular buffer structure ? (fixed array + modulo)
+
     std::deque<T> m_queue;
 
     mutable std::mutex m_mutex;