CODEWITHSUNDEEP
pythonsleepzeromq
mmtauqir
mmtauqir

Reputation: 9309

Sleep after ZMQ connect?

In a ROUTER-ROUTER setup, after I connect one ROUTER socket to another, if I don't sleep (for say 0.1s or so) after I connect() to the other ROUTER socket, the send() usually doesn't go through (although it sometimes does, by chance).

  1. Is there a way to make sure I am connected before I send?
  2. Why aren't the send()s queued and properly executed until the connection is made?

Also, this is not about whether the server on the other end is alive but rather that I send() too soon after I connect() and somehow it fails. I am not sure why.

Upvotes: 5

Views: 470

Answers (1)

Guido Simone
Guido Simone

Reputation: 7952

Is there a way to make sure I am connected before I send?

Not directly. The recommended approach is to use something like the Freelanch Protocol and keep pinging until you receive a response. If you stop receiving responses to your pings you should consider yourself disconnected.

Why aren't the send()s queued and properly executed until the connection is made?

A router cannot send a message to a peer until both sides have completed an internal ZeroMQ handshake. That's just the way it works, since the ROUTER requires the ID of its peer in order to "route". Apparently sleeping for .1sec is the right amount of time on your dev system. If you need the ability to connect and then send without sleeping or retrying, then you need to use a different pattern.

For example, with DEALER-ROUTER, a DEALER client can connect and immediately send and ZeroMQ will queue the message until it is delivered. The reason the works is that the DEALER does not require the ID of the peer - since it does not "route". When the ROUTER server receives the message, that handshake is already complete so it can respond right away without sleeping.

Upvotes: 2

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