TH_CLEAN_3: Use of non-blocking try_pop() when possible,

AudioThread concurrent access hardening and simplified,
and misc.

src/sdr/SDRPostThread.cpp

@@ -215,11 +215,14 @@ void SDRPostThread::run() {
         if (doUpdate) {
             updateActiveDemodulators();
         }
-    }
+    } //end while
     
-    if (iqVisualQueue && !iqVisualQueue->empty()) {
-        DemodulatorThreadIQData *visualDataDummy;
-        iqVisualQueue->pop(visualDataDummy);
+    //TODO: Why only 1 element was removed before ?
+    DemodulatorThreadIQData *visualDataDummy;
+    while (iqVisualQueue && iqVisualQueue->try_pop(visualDataDummy)) {
+        //nothing
+        //TODO: What about the refcounts ?
+        
     }
 
     //    buffers.purge();

src/sdr/SoapySDRThread.cpp

@@ -162,6 +162,7 @@ void SDRThread::readStream(SDRThreadIQDataQueue* iqDataOutQueue) {
     int nElems = numElems.load();
     int mtElems = mtuElems.load();
 
+    //If overflow occured on the previous readStream(), transfer it in inpBuffer now
     if (numOverflow > 0) {
         int n_overflow = numOverflow;
         if (n_overflow > nElems) {
@@ -176,9 +177,18 @@ void SDRThread::readStream(SDRThreadIQDataQueue* iqDataOutQueue) {
         }
     }
     
+    //attempt readStream() at most nElems, by mtElems-sized chunks, append inpBuffer.
     while (n_read < nElems && !stopping) {
         int n_requested = nElems-n_read;
+        
         int n_stream_read = device->readStream(stream, buffs, mtElems, flags, timeNs);
+
+        //if the n_stream_read <= 0, bail out from reading. 
+        if (n_stream_read <= 0) {
+            break;
+        }
+
+        //sucess read beyond nElems, with overflow
         if ((n_read + n_stream_read) > nElems) {
             memcpy(&inpBuffer.data[n_read], buffs[0], n_requested * sizeof(float) * 2);
             numOverflow = n_stream_read-n_requested;