[EventHub] Fix race condition when buffered mode is enabled (Azure#34712)

* Protects buffer append from race condition

* Improves current batch flushing consistency

* Update azure-eventhub CHANGELOG.md

Author: falcaopetri

sdk/eventhub/azure-eventhub/CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Bugs Fixed
 
+- Fixed a bug where using `EventHubProducerClient` in buffered mode could potentially drop a buffered message without actually sending it. ([#34712](https://github.com/Azure/azure-sdk-for-python/pull/34712))
+
 ### Other Changes
 
 - Updated network trace logging to replace `None` values in AMQP connection info with empty strings as per the OpenTelemetry specification.

sdk/eventhub/azure-eventhub/azure/eventhub/_buffered_producer/_buffered_producer.py

@@ -105,24 +105,22 @@ def put_events(self, events, timeout_time=None):
             raise OperationTimeoutError(
                 "Failed to enqueue events into buffer due to timeout."
             )
-        try:
-            # add single event into current batch
-            self._cur_batch.add(events)
-        except AttributeError:  # if the input events is a EventDataBatch, put the whole into the buffer
-            # if there are events in cur_batch, enqueue cur_batch to the buffer
-            with self._lock:
+        with self._lock:
+            try:
+                # add single event into current batch
+                self._cur_batch.add(events)
+            except AttributeError:  # if the input events is a EventDataBatch, put the whole into the buffer
+                # if there are events in cur_batch, enqueue cur_batch to the buffer
                 if self._cur_batch:
                     self._buffered_queue.put(self._cur_batch)
                 self._buffered_queue.put(events)
-            # create a new batch for incoming events
-            self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
-        except ValueError:
-            # add single event exceeds the cur batch size, create new batch
-            with self._lock:
+                # create a new batch for incoming events
+                self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
+            except ValueError:
+                # add single event exceeds the cur batch size, create new batch
                 self._buffered_queue.put(self._cur_batch)
-            self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
-            self._cur_batch.add(events)
-        with self._lock:
+                self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
+                self._cur_batch.add(events)
             self._cur_buffered_len += new_events_len
 
     def failsafe_callback(self, callback):
@@ -146,6 +144,7 @@ def flush(self, timeout_time=None, raise_error=True):
             _LOGGER.info("Partition: %r started flushing.", self.partition_id)
             if self._cur_batch:  # if there is batch, enqueue it to the buffer first
                 self._buffered_queue.put(self._cur_batch)
+                self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
             while self._buffered_queue.qsize() > 0:
                 remaining_time = timeout_time - time.time() if timeout_time else None
                 if (remaining_time and remaining_time > 0) or remaining_time is None:
@@ -197,9 +196,6 @@ def flush(self, timeout_time=None, raise_error=True):
                     break
             # after finishing flushing, reset cur batch and put it into the buffer
             self._last_send_time = time.time()
-            #reset buffered count
-            self._cur_buffered_len = 0
-            self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
             _LOGGER.info("Partition %r finished flushing.", self.partition_id)
 
     def check_max_wait_time_worker(self):

sdk/eventhub/azure-eventhub/azure/eventhub/aio/_buffered_producer/_buffered_producer_async.py

@@ -105,24 +105,22 @@ async def put_events(self, events, timeout_time=None):
             raise OperationTimeoutError(
                 "Failed to enqueue events into buffer due to timeout."
             )
-        try:
-            # add single event into current batch
-            self._cur_batch.add(events)
-        except AttributeError:  # if the input events is a EventDataBatch, put the whole into the buffer
-            # if there are events in cur_batch, enqueue cur_batch to the buffer
-            async with self._lock:
+        async with self._lock:
+            try:
+                # add single event into current batch
+                self._cur_batch.add(events)
+            except AttributeError:  # if the input events is a EventDataBatch, put the whole into the buffer
+                # if there are events in cur_batch, enqueue cur_batch to the buffer
                 if self._cur_batch:
                     self._buffered_queue.put(self._cur_batch)
                 self._buffered_queue.put(events)
-            # create a new batch for incoming events
-            self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
-        except ValueError:
-            # add single event exceeds the cur batch size, create new batch
-            async with self._lock:
+                # create a new batch for incoming events
+                self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
+            except ValueError:
+                # add single event exceeds the cur batch size, create new batch
                 self._buffered_queue.put(self._cur_batch)
-            self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
-            self._cur_batch.add(events)
-        async with self._lock:
+                self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
+                self._cur_batch.add(events)
             self._cur_buffered_len += new_events_len
 
     def failsafe_callback(self, callback):
@@ -200,9 +198,6 @@ async def _flush(self, timeout_time=None, raise_error=True):
                 break
         # after finishing flushing, reset cur batch and put it into the buffer
         self._last_send_time = time.time()
-        #reset curr_buffered
-        self._cur_buffered_len = 0
-        self._cur_batch = EventDataBatch(self._max_message_size_on_link, amqp_transport=self._amqp_transport)
         _LOGGER.info("Partition %r finished flushing.", self.partition_id)
 
     async def check_max_wait_time_worker(self):