rcvtimeo values not honored by recv

[caffeine-overload]

It seems like regardless of the value for rcvtimeo set, recv is waiting for a message for ever.

Example

With a local PUB socket already set up:

using ZMQ

s1 = Socket(SUB)
s1.rcvtimeo = 5000

connect(s1, "tcp://localhost:5000")
subscribe(s1, "HHHHH") # a topic that never gets published to
a = recv(s1, String)

Expected behavior

recv gives up after 5 seconds

Actual behavior

recv hangs

More info

Using Julia Version 1.1.0

Calling msg_recv without the ZMQ_DONTWAIT flag, i.e. requesting blocking mode from zeromq, results in desired behavior. Although obviously you then don't have the convenience functions like recv(socket::Socket, ::Type{T}).

Maybe having an optional argument in recv to not use the ZMQ_DONTWAIT flag could be a simple fix for the moment.

[vtjnash]

Duplicate of #87

[vtjnash]

I'm not sure what that field is for, but in general Julia is designed to give you synchronous options with lightweight Tasks so that you don't need to manage these timeouts manually.

[caffeine-overload]

I'm not sure what that field is for

You mean ZMQ_DONTWAIT?

[vtjnash]

s1.rcvtimeo

[caffeine-overload]

If ZMQ_DONTWAIT is not used, msg_recv will wait for up to rcvtimeo milliseconds for a message to arrive. If one doesn't, it will return and set the EAGAIN error.

Even if there is a way to emulate this in julia using tasks, I still think the functionality in zmq itself should be made available. I also don't believe Julia yet has a reliable way to terminate an overrunning task easily.

[caffeine-overload]

I made my own function to suit my (very simple - just a script that receives and handles values - but I know that messages arrive at least every milliseconds, so a timeout indicates a dead connection) particular use case, I'm just leaving it here in case anyone else has a similar use case.

function zmq_receive(socket::ZMQ.Socket)::Union{String, Missing}
    zmsg = ZMQ.msg_init()
    status = ZMQ.msg_recv(socket, zmsg, 0)
    if status == -1
        if ZMQ.zmq_errno() == ZMQ.EAGAIN
            @warn "Socket timeout"
            return missing
        else
            throw(StateError(ZMQ.jl_zmq_error_str()))
        end
    end
    return ZMQ.unsafe_copy(String, zmsg)
end

This functions honors rcvtimeo, but probably will block a task without letting julia switch to a different one