CODEWITHSUNDEEP
windowszeromqnonblocking
ebyrob
ebyrob

Reputation: 674

Why is zmq_recv() with a ZMQ_DONTWAIT returning an errno == 0 instead of EAGAIN?

I'm writing a small test app using ZeroMQ.

One test scenario I have is when there is no server running to connect to.

So, I'm passing ZMQ_DONTWAIT to zmq_recv() in that scenario expecting an error of EAGAIN but instead getting errno value of 0.

Sample client code below:

int rc;

void *context = zmq_ctx_new();
void *requester = zmq_socket(context, ZMQ_REQ);
int nLingerOption = 0;
rc = zmq_setsockopt(requester, ZMQ_LINGER, &nLingerOption, sizeof(nLingerOption));
rc = zmq_connect(requester, "tcp://127.0.0.1:5555");

int nSendLen = zmq_send(requester, "M", 1, 0);

char buffer[1000];
int nRecvLen = zmq_recv(requester, buffer, sizeof(buffer)-1, ZMQ_DONTWAIT);

if( nRecvLen < 0 )
    printf("errno = %d\n", errno);

Why would the output be 0 instead of EAGAIN (defined as 11 on my system).

EDIT: This is running ZeroMQ version 4.1

Upvotes: 0

Views: 2041

Answers (1)

Jason
Jason

Reputation: 13766

The answer is hiding in your windows tag (thanks for including that). Relevant: http://api.zeromq.org/4-1:zmq-errno

Specifically:

The zmq_errno() function is provided to assist users on non-POSIX systems who are experiencing issues with retrieving the correct value of errno directly. Specifically, users on Win32 systems whose application is using a different C run-time library from the C run-time library in use by ØMQ will need to use zmq_errno() for correct operation.

You should be using zmq_errno() as opposed to accessing errno directly.

Upvotes: 1

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