[rabbitmq-discuss] Java waitForConfirmsOrDie(timeout) can block indefinitely

[Stuart Sierra]

Hello list,

It appears that flow control can cause the Java API to block indefinitely
on the call to Channel.waitForConfirmsOrDie(long timeout), regardless of
the timeout value.

Is this intentional?

I tested this with RabbitMQ 3.2.0 and the official Java client 3.2.0.

Steps to reproduce:

   1. Start a RabbitMQ broker
   2. Connect with the Java client
   3. Create a Channel and call `confirmSelect`
   4. Run `rabbitmqctl set_vm_memory_high_watermark 0.0`
   5. Call `basicPublish` to publish a message
   6. Call `Channel.waitForConfirmsOrDie(1000L)`
   7. Wait for more than 1 second: no exception
   8. Run `rabbitmqctl set_vm_memory_high_watermark 0.4`
   9. TimeoutException is thrown

I think this is because ChannelN.waitForConfirmsOrDie(long timeout) catches
TimeoutException and calls:

close(AMQP.PRECONDITION_FAILED, "TIMEOUT WAITING FOR ACK");


The call to `close` blocks indefinitely because the RabbitMQ connection is
blocked. The TimeoutException does not get thrown until after the
connection is unblocked.

As a workaround, I am calling `Channel.waitForConfirms(long timeout)` and
throwing an exception if returns false.

Regards,
Stuart Sierra
Cognitect, Inc.
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