gistfile1.txt

Using keepalive based channel connectivity checks and TCP_USER_TIMEOUT to avoid blocking:
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import grpc
import time
import helloworld_pb2
import helloworld_pb2_grpc

def run():
    channel_opts = [
        (
            # Interval at which grpc will send keepalive pings
            'grpc.keepalive_time_ms',
            1000
        ),
        (
            # Amount of time grpc waits for a keepalive ping to be 
            # acknowledged before deeming the connection unhealthy and closing
            # this also sets TCP_USER_TIMEOUT for the underlying socket to this value
            'grpc.keepalive_timeout_ms',
            500
        )
    ]
    channel = grpc.insecure_channel("localhost:1234", options=channel_opts)
    stub = helloworld_pb2_grpc.GreeterStub(channel)
    
    while True:
        # Some large message
        msg = 'Hello' * 100000
        
        # Check that the connectivity state of the channel is connected (2)
        # Passing True here tells the channel attempt to connect if disconnected
        # https://github.com/grpc/grpc/blob/2cec9c5344014db548448bd7fbbe04e7c33635be/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi#L469
        if channel._channel.check_connectivity_state(True) == 2:
            try:
                # Make RPC call supplying a sane timeout value
                response = stub.SayHello(helloworld_pb2.HelloRequest(name=msg), timeout=0.3)
            except RpcError as e:
                # Handle timeouts here
                pass
            else:
                # Do something with response
        time.sleep(0.01)