wait with a condition variable instead of a this_thread::sleep_for so that waiting can be cancelled when we stop/shutdown the data thread (see #151)

ixwebsocket/IXWebSocket.cpp

@@ -169,6 +169,7 @@ namespace ix
             // wait until working thread will exit
             // it will exit after close operation is finished
             _stop = true;
+            _sleepCondition.notify_one();
             _thread.join();
             _stop = false;
         }
@@ -282,8 +283,8 @@ namespace ix
             // Only sleep if we are retrying
             if (duration.count() > 0)
             {
-                // to do: make sleeping conditional
-                std::this_thread::sleep_for(duration);
+                std::unique_lock<std::mutex> lock(_sleepMutex);
+                _sleepCondition.wait_for(lock, duration);
             }
 
             // Try to connect synchronously

ixwebsocket/IXWebSocket.h

@@ -22,6 +22,7 @@
 #include <mutex>
 #include <string>
 #include <thread>
+#include <condition_variable>
 
 namespace ix
 {
@@ -140,6 +141,10 @@ namespace ix
         static const uint32_t kDefaultMaxWaitBetweenReconnectionRetries;
         uint32_t _maxWaitBetweenReconnectionRetries;
 
+        // Make the sleeping in the automatic reconnection cancellable
+        std::mutex _sleepMutex;
+        std::condition_variable _sleepCondition;
+
         std::atomic<int> _handshakeTimeoutSecs;
         static const int kDefaultHandShakeTimeoutSecs;