Support multiple receivers on a topic with the same message queue name (iox::runtime::PoshRuntime::getInstance("/xxx"))?

[callalilychen]

I get the following error message, when I try to start an example subscriber multiple times:

$ ./build/iceoryx_examples/icedelivery/ice-subscriber-bare-metal 
Receiving: 1249
Receiving: 1250
Receiving: 1251

$ ./build/iceoryx_examples/icedelivery/ice-subscriber-bare-metal
2020-01-22 00:45:03.179 [Warning]: MQ still there, doing an unlink of /subscriber-bare-metal
2020-01-22 00:45:33.183 [ Error ]: ICEORYX error! MQ_INTERFACE__REG_ACK_NO_RESPONSE
ice-subscriber-bare-metal: /home/wenwen/tools/iceoryx-rs/iceoryx/iceoryx_utils/source/error_handling/error_handling.cpp:53: static void iox::ErrorHandler::ReactOnErrorLevel(iox::ErrorLevel, const char*): Assertion `false' failed.
fish: “./build/iceoryx_examples/icedel…” terminated by signal SIGABRT (Abort)

Is it possible to support multiple receivers on a topic with the same message queue name? Or it is not allowed because of some good reasons? Better error message for such "misuse" would be very nice.

[elBoberido]

After some thinking, this is probably something the application should take care of.
The MQ_APP_NAME from iox::runtime::PoshRuntime::getInstance("/xxx") is the name of the message queue which will be opened by the application before it registers at RouDi.
The application could just append the PID to MQ_APP_NAME.
Be carefully though, if the application has a publisher, there might be strange behaviour until #25 is fixed.

[budrus]

Good point @callalilychen .

You can have multiple receivers/subscribers on a topic but each application must register with a unique name. The RouDi daemon prints a warning but the error message on the application side should be clearer.

You could append an instance ID that you provide as command line parameter. The proposal of @elBoberido would also be an option. But then you maybe would not recognize it if you accidentally start an application twice. If #25 is implemented you would then have two writers on the same topic. If this is not what you had in mind it may took a while until you have deciphered the puzzle ;-)

[mossmaurice]

As #25 is nearly done and iceoryx 1.0 on the horizon, I'll close this issue.