我正在运行pubsub使用者，该使用者以大约每秒一的速率处理传入的消息。事情通常运行良好，但是，每隔几天或每隔几小时，我们偶尔会看到pubsub模块内部线程引发的异常，但我不清楚如何捕获它们。这是一个典型示例（也会出现其他类似的跟踪，但消息稍有不同）：
Exception in thread Thread-LeaseMaintainer:
Traceback (most recent call last):
File "/usr/local/lib/python3.6/site-packages/google/api_core/grpc_helpers.py", line 57, in error_remapped_callable
return callable_(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/grpc/_channel.py", line 549, in __call__
return _end_unary_response_blocking(state, call, False, None)
File "/usr/local/lib/python3.6/site-packages/grpc/_channel.py", line 466, in _end_unary_response_blocking
raise _Rendezvous(state, None, None, deadline)
grpc._channel._Rendezvous: <_Rendezvous of RPC that terminated with:
status = StatusCode.UNAVAILABLE
details = "channel is in state TRANSIENT_FAILURE"
debug_error_string = "{"created":"@1554568036.075280756","description":"channel is in state TRANSIENT_FAILURE","file":"src/core/ext/filters/client_channel/client_channel.cc","file_line":2294,"grpc_status":14}"
>
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/usr/local/lib/python3.6/site-packages/google/api_core/retry.py", line 179, in retry_target
return target()
File "/usr/local/lib/python3.6/site-packages/google/api_core/timeout.py", line 214, in func_with_timeout
return func(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/google/api_core/grpc_helpers.py", line 59, in error_remapped_callable
six.raise_from(exceptions.from_grpc_error(exc), exc)
File "<string>", line 3, in raise_from
google.api_core.exceptions.ServiceUnavailable: 503 channel is in state TRANSIENT_FAILURE
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/usr/local/lib/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/usr/local/lib/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/usr/local/lib/python3.6/site-packages/google/cloud/pubsub_v1/subscriber/_protocol/leaser.py", line 146, in maintain_leases
[requests.ModAckRequest(ack_id, p99) for ack_id in ack_ids]
File "/usr/local/lib/python3.6/site-packages/google/cloud/pubsub_v1/subscriber/_protocol/dispatcher.py", line 152, in modify_ack_deadline
self._manager.send(request)
File "/usr/local/lib/python3.6/site-packages/google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py", line 268, in send
self._send_unary_request(request)
File "/usr/local/lib/python3.6/site-packages/google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py", line 259, in _send_unary_request
ack_deadline_seconds=deadline,
File "/usr/local/lib/python3.6/site-packages/google/cloud/pubsub_v1/_gapic.py", line 45, in <lambda>
fx = lambda self, *a, **kw: wrapped_fx(self.api, *a, **kw) # noqa
File "/usr/local/lib/python3.6/site-packages/google/cloud/pubsub_v1/gapic/subscriber_client.py", line 723, in modify_ack_deadline
request, retry=retry, timeout=timeout, metadata=metadata
File "/usr/local/lib/python3.6/site-packages/google/api_core/gapic_v1/method.py", line 143, in __call__
return wrapped_func(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/google/api_core/retry.py", line 270, in retry_wrapped_func
on_error=on_error,
File "/usr/local/lib/python3.6/site-packages/google/api_core/retry.py", line 199, in retry_target
last_exc,
File "<string>", line 3, in raise_from
google.api_core.exceptions.RetryError: Deadline of 600.0s exceeded while calling functools.partial(<function _wrap_unary_errors.<locals>.error_remapped_callable at 0x7f86228cd400>, subscription: "projects/xxxxx-dev/subscriptions/telemetry-sub"
ack_deadline_seconds: 10
ack_ids: "QBJMJwFESVMrQwsqWBFOBCEhPjA-RVNEUAYWLF1GSFE3GQhoUQ5PXiM_NSAoRRoHIGoKOUJdEmJoXFx1B1ALEHQoYnxvWRYFCEdReF1YHQdodGxXOFUEHnN1Y3xtWhQDAEFXf3f8gIrJ38BtZho9WxJLLD5-LDRFQV4"
, metadata=[('x-goog-api-client', 'gl-python/3.6.8 grpc/1.19.0 gax/1.8.2 gapic/0.40.0')]), last exception: 503 channel is in state TRANSIENT_FAILURE
Thread-ConsumeBidirectionalStream caught unexpected exception Deadline of 600.0s exceeded while calling functools.partial(<function _wrap_unary_errors.<locals>.error_remapped_callable at 0x7f86228cda60>, subscription: "projects/xxxxx-dev/subscriptions/telemetry-sub"
ack_deadline_seconds: 10
ack_ids: "QBJMJwFESVMrQwsqWBFOBCEhPjA-RVNEUAYWLF1GSFE3GQhoUQ5PXiM_NSAoRRoHIGoKOUJdEmJoXFx1B1ALEHQoYnxvWRYFCEdReF1YHAdodGxXOFUEHnN1aXVoWxAIBEdXeXf8gIrJ38BtZho9WxJLLD5-LDRFQV4"
, metadata=[('x-goog-api-client', 'gl-python/3.6.8 grpc/1.19.0 gax/1.8.2 gapic/0.40.0')]), last exception: 503 channel is in state TRANSIENT_FAILURE and will exit.
（在这种特殊情况下，订户收到了几个类似的错误，并且完全停止使用消息（没有主线程退出）；但是，在其他此类库错误的情况下，还观察到其他行为。）
我们的代码大致如下（略有简化）：
client = pubsub_v1.SubscriberClient()
flow_control = pubsub_v1.types.FlowControl(max_messages=500)
future = client.subscribe(subscription_path, callback=callback,
flow_control=flow_control)
...
try:
future.result(timeout=1)
except pubsub_v1.exceptions.TimeoutError:
pass
except _Rendezvous as exc:
logger.error('Got Rendezvous error in subscriber. Retrying in 1s. '
f'Detail: {exc}')
# NEVER GET HERE
time.sleep(1)
continue
except RetryError as exc:
logger.error('Got RetryError in subscriber. Retrying in 1s. '
f'Detail: {exc}')
# NEVER GET HERE
time.sleep(1)
continue
except Exception as exc: # pylint: disable=broad-except
logger.exception('Got uncaught exception in subscriber or callback ...')
# NEVER GET HERE
没有任何异常分支。这使我认为，尽管文档（GCP PubSub Docs）相反，该异常是在某个后台线程中发生的，并且未由future.result（）调用报告。我已经阅读了许多github问题，仔细阅读了文档，并搜索了与此相关的SO问题，但是我一直找不到能够真正捕获此类错误的解决方案。任何帮助或建议，将不胜感激。
版本：
答案 0 :(得分：1)
没有必要捕获这些内部错误并进行处理。它们是库与Google Cloud Pub / Sub服务的连接中的暂时性错误，库本身应处理这些错误。如果没有，特别是如果它阻止了进一步的消息而又没有重新启动，则表明它是一个错误，应该在GitHub repo for the Python client library中输入一个问题。