perf(spanner): optimize built-in metrics hot path and harden concurrency

packages/google-cloud-spanner/google/cloud/spanner_v1/metrics/constants.py

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Any
+
 BUILT_IN_METRICS_METER_NAME = "gax-python"
 NATIVE_METRICS_PREFIX = "spanner.googleapis.com/internal/client"
 SPANNER_RESOURCE_TYPE = "spanner_instance_client"
@@ -21,6 +23,18 @@
 GOOGLE_CLOUD_REGION_GLOBAL = "global"
 SPANNER_METHOD_PREFIX = "/google.spanner.v1."
 
+
+def _safe_decode_utf8(value: Any) -> str:
+    """Safely decode bytes to str or return str representation without raising."""
+    if value is None:
+        return ""
+    if isinstance(value, str):
+        return value
+    if isinstance(value, bytes):
+        return value.decode("utf-8", errors="replace")
+    return str(value)
+
+
 # Monitored resource labels
 MONITORED_RES_LABEL_KEY_PROJECT = "project_id"
 MONITORED_RES_LABEL_KEY_INSTANCE = "instance_id"

packages/google-cloud-spanner/google/cloud/spanner_v1/metrics/metrics_capture.py

@@ -108,6 +108,7 @@ def __exit__(self, exc_type, exc_value, traceback):
                 except Exception:
                     pass
         finally:
+            # Reset the context var using the token
             try:
                 SpannerMetricsTracerFactory.reset_current_tracer(token)
             except ValueError: