Allow calling mark() functions when not tracing

src/etwtrace/__init__.py

@@ -169,24 +169,41 @@ def enable_if(enable_var, type_var):
     tracer.enable()
 
 
+def is_active():
+    """Returns True if tracing is active."""
+    return bool(_tracer)
+
+
 def mark(name):
     """Emits a mark event with the provided text."""
-    if not _tracer:
-        raise RuntimeError("unable to mark when global tracer is not enabled")
-    _tracer.mark(name)
+    if _tracer:
+        _tracer.mark(name)
+    else:
+        import warnings
+        warnings.warn("Unable to mark when global tracer is not enabled", RuntimeWarning)
+
+
+class _NullRange:
+    def __enter__(self): return self
+    def __exit__(self, *exc_info): pass
 
 
 def mark_range(name):
     """Context manager to emit start/stop mark events with the provided text."""
-    if not _tracer:
-        raise RuntimeError("unable to mark when global tracer is not enabled")
-    return _tracer.mark_range(name)
+    if _tracer:
+        return _tracer.mark_range(name)
+    else:
+        import warnings
+        warnings.warn("Unable to mark when global tracer is not enabled", RuntimeWarning)
+        return _NullRange()
 
 
 def _mark_stack(mark):
-    if not _tracer:
-        raise RuntimeError("unable to mark when global tracer is not enabled")
-    return _tracer._mark_stack(mark)
+    if _tracer:
+        return _tracer._mark_stack(mark)
+    else:
+        import warnings
+        warnings.warn("Unable to mark when global tracer is not enabled", RuntimeWarning)
 
 
 _TEMP_PROFILE = None

tests/test_etw.py

@@ -234,6 +234,22 @@ def test_but_do_we_instrument():
     )
 
 
+def test_but_are_we_inactive():
+    assert etwtrace.is_active() is False
+
+
+def test_but_do_we_warn_on_mark():
+    with pytest.warns(RuntimeWarning):
+        etwtrace.mark("Test mark without tracing")
+
+    with pytest.warns(RuntimeWarning):
+        with etwtrace.mark_range("Test mark without tracing"):
+            pass
+
+    with pytest.warns(RuntimeWarning):
+        etwtrace._mark_stack("Test mark without tracing")
+
+
 def test_basic(trace_events):
     funcs = set()
     with trace_events("basic.py", providers=['Python']) as etl: