Fix BoundedAttributes to log drop warning only once per record

.changelog/5727.fixed

@@ -0,0 +1 @@
+`opentelemetry-api`: log the ``BoundedAttributes`` drop warning only once per record

opentelemetry-api/src/opentelemetry/attributes/__init__.py

@@ -153,6 +153,9 @@ def __init__(
         self.dropped = 0
         self.max_value_len = max_value_len
         self._lock = threading.Lock()
+        # The spec allows the limit log to be emitted at most once per record, so track
+        # it separately from ``dropped``, which also counts other kinds of drops.
+        self._dropped_logged = False
         # setting False before adding items
         self._immutable = False
         if attributes:
@@ -203,9 +206,11 @@ def _setitem_locked(self, key: str, value: types.AnyValue) -> None:
         if key in self._dict:
             del self._dict[key]
         if self.maxlen is not None and len(self._dict) >= self.maxlen:
-            _logger.warning(
-                "Attributes dict is full. Dropping the oldest key-value pair from attributes to make space for the new key-value pair.",
-            )
+            if not self._dropped_logged:
+                self._dropped_logged = True
+                _logger.warning(
+                    "Attributes dict is full. Dropping the oldest key-value pair from attributes to make space for the new key-value pair.",
+                )
             # Dictionaries are insertion ordered in Python, this is the recommended way to get the oldest value.
             del self._dict[next(iter(self._dict.keys()))]
             self.dropped += 1

opentelemetry-api/tests/attributes/test_attributes.py

@@ -112,6 +112,29 @@ def test_maxlen_reached(self):
         self.assertEqual(bdict["second"], "another")
         self.assertEqual(bdict.dropped, 1)
 
+    def test_maxlen_reached_logs_warning_once(self):
+        bdict = BoundedAttributes(2, immutable=False)
+        with self.assertLogs("opentelemetry", level="WARNING") as cm:
+            for idx in range(5):
+                bdict[f"key-{idx}"] = idx
+
+        full_warnings = [warning for warning in cm.output if "Attributes dict is full" in warning]
+        self.assertEqual(len(full_warnings), 1)
+        self.assertEqual(len(bdict), 2)
+        self.assertEqual(bdict.dropped, 3)
+
+    def test_maxlen_reached_logs_warning_after_invalid_key_drop(self):
+        bdict = BoundedAttributes(2, immutable=False)
+        with self.assertLogs("opentelemetry", level="WARNING") as cm:
+            bdict[1] = 2
+            bdict["first"] = 1
+            bdict["second"] = 2
+            bdict["third"] = 3
+
+        full_warnings = [warning for warning in cm.output if "Attributes dict is full" in warning]
+        self.assertEqual(len(full_warnings), 1)
+        self.assertEqual(bdict.dropped, 2)
+
     def test_negative_maxlen_not_allowed(self):
         with self.assertRaises(ValueError):
             BoundedAttributes(-1)