Don't get stuck when closing application just because some Demodulators refuse to die

src/CubicSDR.cpp

@@ -405,7 +405,7 @@ int CubicSDR::OnExit() {
     std::cout << "Terminating All Demodulators.." << std::endl;
     demodMgr.terminateAll();
     //wait for effective death of all demodulators before continuing.
-    demodMgr.garbageCollect(true);
+    demodMgr.garbageCollect(true, 3000);
    
     std::cout << "Terminating Visual Processor threads.." << std::endl;
     spectrumVisualThread->terminate();

src/demod/DemodulatorMgr.cpp

@@ -278,7 +278,22 @@ DemodulatorInstance *DemodulatorMgr::getLastDemodulatorWith(const std::string& t
 	return nullptr;
 }
 
-void DemodulatorMgr::garbageCollect(bool forcedGC) {
+void DemodulatorMgr::garbageCollect(bool forcedGC, int maxWaitForTerminationMs) {
+    
+#define SPIN_WAIT_SLEEP_MS 5
+
+    //this is a stupid busy plus sleep loop
+    int nbCyclesToWait = 0;
+
+    if (maxWaitForTerminationMs <= 0) {
+        nbCyclesToWait = std::numeric_limits<int>::max();
+    }
+    else {
+
+        nbCyclesToWait = (maxWaitForTerminationMs / SPIN_WAIT_SLEEP_MS) + 1;
+    }
+
+    int currentWaitCycle = 0;
 
     std::lock_guard < std::mutex > lock(deleted_demods_busy);
 
@@ -306,7 +321,14 @@ void DemodulatorMgr::garbageCollect(bool forcedGC) {
             }
         } //end while
         //stupid busy-wait loop
-        std::this_thread::sleep_for(std::chrono::milliseconds(5));
+        std::this_thread::sleep_for(std::chrono::milliseconds(SPIN_WAIT_SLEEP_MS));
+
+        currentWaitCycle++;
+
+        if (currentWaitCycle >= nbCyclesToWait) {
+            std::cout << "ERROR: DemodulatorMgr::garbageCollect() has not terminated in time ! (> " << (currentWaitCycle * SPIN_WAIT_SLEEP_MS) << " ms)" << std::endl << std::flush;
+            return;
+        }
     } //end while not empty
 }
 

src/demod/DemodulatorMgr.h

@@ -73,7 +73,9 @@ public:
     //all deleted demodulators are effectively GCed.
     //else: (default) the method test for effective termination
     //and GC one demod per call. 
-    void garbageCollect(bool forcedGC = false);
+    // if forcedGC = true and maxWaitForTerminationMs > 0, do not
+    //block the method more than maxWaitForTerminationMs millisecs before returning.
+    void garbageCollect(bool forcedGC = false, int maxWaitForTerminationMs = 0);
     
 private: