deprecate thread unsafe isClosed() in DataInputQueue, DataOutputQueue

- partial fix luxonis#520

include/depthai/device/DataQueue.hpp

@@ -43,8 +43,10 @@ class DataOutputQueue {
 
     /**
      * Check whether queue is closed
+     *
+     * @warning This function is thread-unsafe and may return incorrect values.
      */
-    bool isClosed() const;
+    [[deprecated("thread-unsafe and may return incorrect values")]] bool isClosed() const;
 
     /**
      * Closes the queue and the underlying thread
@@ -355,8 +357,10 @@ class DataInputQueue {
 
     /**
      * Check whether queue is closed
+     *
+     * @warning This function is thread-unsafe and may return incorrect values.
      */
-    bool isClosed() const;
+    [[deprecated("thread-unsafe and may return incorrect values")]] bool isClosed() const;
 
     /**
      * Closes the queue and the underlying thread

src/device/DataQueue.cpp

@@ -83,6 +83,10 @@ DataOutputQueue::DataOutputQueue(const std::shared_ptr<XLinkConnection> conn, co
     });
 }
 
+// BUGBUG this function is thread-unsafe. The idea of "isClosed" is ephemerial and
+// since there is no mutex lock, its state is outdated and invalid even before
+// the logical NOT in this function. This calculated boolean then continues to degrade
+// in validity as it is returned by value to the caller
 bool DataOutputQueue::isClosed() const {
     return !running;
 }
@@ -220,6 +224,10 @@ DataInputQueue::DataInputQueue(
     });
 }
 
+// BUGBUG this function is thread-unsafe. The idea of "isClosed" is ephemerial and
+// since there is no mutex lock, its state is outdated and invalid even before
+// the logical NOT in this function. This calculated boolean then continues to degrade
+// in validity as it is returned by value to the caller
 bool DataInputQueue::isClosed() const {
     return !running;
 }