when to shutdown channel?

[sj602]

When is the proper time to close the channel?
I want to keep a persistent connection to a gRPC server so I don't want to close it actually.
However, I got an exception like this intermittently as a gRPC client. And what is weird is that the whole business logic worked properly.

*~*~*~ Channel ManagedChannelImpl{logId=8, target=SOME_TARGET_ADDRESS_AND_PORT} was not shutdown properly!!! ~*~*~*
    Make sure to call shutdown()/shutdownNow() and wait until awaitTermination() returns true.

After a few researches, I found the reason for the exception which is that the reference to the channel is going to be removed by GC but is not properly shutdown. And even though it's an exception, it is for the warning purpose to close the channel explicitly.

• What really triggers grpc-java to throw the exception? Is it like the previous channel is closed because of some random causes and the new channel is created internally, so that the previous channel becomes the target for GC?
• What if I don't want to close the channel and want to use it forever as long as the process is alive?

[ejona86]

Use channels as long as you can. That message means that something in your jwm leaked a channel and it was GCed. The stack trace shows where the channel was allocated, to make it easier for you to track down where it leaked.

[Jasper-M]

The advice in the log message is kind of confusing. By looking at the code it seems that if shutdown() was called at all, this message won't be logged. So properly awaiting termination won't change anything, but the message makes it sound like it will. It may be better if the message clearly states that a channel was leaked without shutting it down, and perhaps leave awaitTermination() for the shutdown() javadoc.