I'm having an issue with client disconnection using a Python gRPC server
with a unary-stream procedure. I may have missed something in the
documentation, but multiple attempts of checking whether or not the client
is still active have all failed.
My hope is to find a way for the Servicer to detect when to stop generating
values when a client disconnects. A client subscribes to a stream of
updates once and receives all changes to the server state for an unbounded
amount of time. The actual server implementation should also send values
regularly on a heartbeat with low activity. A minimal example is given
below that demonstrates my problem.
class TaskService(proto_grpc.TaskServiceServicer):
def Subscribe(self, request, context):
print 'subscribed'
while True:
time.sleep(1)
print 'sending'
yield proto.TaskState(state='IDLE')
print 'finished'
def main():
server =
grpc.server(concurrent.futures.ThreadPoolExecutor(max_workers=3))
proto_grpc.add_TaskServiceServicer_to_server(
TaskService(),
server,
)
server.add_insecure_port('0.0.0.0:3253')
server.start()
try:
while True:
time.sleep(1)
print 'bump'
finally:
print 'stopping'
server.stop(grace=0)
print 'stopped'
There are two issues at play here. First, if a client subscribes and then
is disconnected forcefully, the server will continue to send updates to
that channel. This means if three clients have *ever* subscribed to this
server, then a fourth may never connect in the future (due to the low
number in the thread pool). This seems wrong, but I may be missing a
setting somewhere.
Second, if a client subscribes and then disconnects, the server will never
shut down completely. The process will hang in an un-killable state. This
does not occur when a client never connects, or if a client connects but
stays connected as the process shuts down.
The following output occurs when the server is killed after a client
connects:
subscribed
bump
sending
bump
sending
^C
stopping
stopped
Traceback (most recent call last):
...
time.sleep(1)
KeyboardInterrupt
sending
<process terminated gracefully>
The following output occurs when the server is killed after a client
disconnects:
subscribed
bump
sending
bump
<client is killed>
sending
bump
^C
stopping
stopped
Traceback (most recent call last):
...
time.sleep(1)
KeyboardInterrupt
sending
<process hangs indefinitely>
I hope there is an easy solution as I simply misunderstood the correct use
to implement a streaming response and apologize in advance if there is.
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