sqlalchemy: make sqlalchemy thread safe (#315)

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#378](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/378))
 - `opentelemetry-instrumentation-wsgi` Reimplement `keys` method to return actual keys from the carrier instead of an empty list.
   ([#379](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/379))
+- `opentelemetry-instrumentation-sqlalchemy` Fix multithreading issues in recording spans from SQLAlchemy
+  ([#315](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/315))
 
 ### Changed
 - Rename `IdsGenerator` to `IdGenerator`

instrumentation/opentelemetry-instrumentation-sqlalchemy/src/opentelemetry/instrumentation/sqlalchemy/engine.py

@@ -12,6 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from threading import local
+from weakref import WeakKeyDictionary
+
 from sqlalchemy.event import listen  # pylint: disable=no-name-in-module
 
 from opentelemetry import trace
@@ -66,12 +69,21 @@ def __init__(self, tracer, engine):
         self.tracer = tracer
         self.engine = engine
         self.vendor = _normalize_vendor(engine.name)
-        self.current_span = None
+        self.cursor_mapping = WeakKeyDictionary()
+        self.local = local()
 
         listen(engine, "before_cursor_execute", self._before_cur_exec)
         listen(engine, "after_cursor_execute", self._after_cur_exec)
         listen(engine, "handle_error", self._handle_error)
 
+    @property
+    def current_thread_span(self):
+        return getattr(self.local, "current_span", None)
+
+    @current_thread_span.setter
+    def current_thread_span(self, span):
+        setattr(self.local, "current_span", span)
+
     def _operation_name(self, db_name, statement):
         parts = []
         if isinstance(statement, str):
@@ -94,34 +106,38 @@ def _before_cur_exec(self, conn, cursor, statement, *args):
             attrs = _get_attributes_from_cursor(self.vendor, cursor, attrs)
 
         db_name = attrs.get(_DB, "")
-        self.current_span = self.tracer.start_span(
+        span = self.tracer.start_span(
             self._operation_name(db_name, statement),
             kind=trace.SpanKind.CLIENT,
         )
-        with trace.use_span(self.current_span, end_on_exit=False):
-            if self.current_span.is_recording():
-                self.current_span.set_attribute(_STMT, statement)
-                self.current_span.set_attribute("db.system", self.vendor)
+        self.current_thread_span = self.cursor_mapping[cursor] = span
+        with trace.use_span(span, end_on_exit=False):
+            if span.is_recording():
+                span.set_attribute(_STMT, statement)
+                span.set_attribute("db.system", self.vendor)
                 for key, value in attrs.items():
-                    self.current_span.set_attribute(key, value)
+                    span.set_attribute(key, value)
 
     # pylint: disable=unused-argument
     def _after_cur_exec(self, conn, cursor, statement, *args):
-        if self.current_span is None:
+        span = self.cursor_mapping.get(cursor, None)
+        if span is None:
             return
-        self.current_span.end()
+
+        span.end()
 
     def _handle_error(self, context):
-        if self.current_span is None:
+        span = self.current_thread_span
+        if span is None:
             return
 
         try:
-            if self.current_span.is_recording():
-                self.current_span.set_status(
+            if span.is_recording():
+                span.set_status(
                     Status(StatusCode.ERROR, str(context.original_exception),)
                 )
         finally:
-            self.current_span.end()
+            span.end()
 
 
 def _get_attributes_from_url(url):