Hi all,
We are seeing unexpected results from 0MQ pub/sub sockets on Windows. As a
foreword, I have never worked with any other kind of sockets before, so
hopefully there is no confusion about how they "should" work; I will, however,
try to be as explicit as possible as to what I'm expecting.
We are using 0MQ through the jzmq library. We are using jzmq 2.2.2 and libzmq
3.2.4 on Windows 7 inside a remote virtual machine.
I have isolated the surprising behavior to the following (java) code:
--
import org.zeromq.ZMQ;
import org.zeromq.ZMQ.Context;
import org.zeromq.ZMQ.Socket;
public class Main {
private static void sleep(int t) {
try {
Thread.sleep(t);
} catch (InterruptedException e) {
}
}
public static void main(String args[]) {
Context context = ZMQ.context(2);
Socket pub = context.socket(ZMQ.PUB);
pub.setSndHWM(60_000);
pub.connect("tcp://127.0.0.1:4001");
Socket sub = context.socket(ZMQ.SUB);
sub.setRcvHWM(20_000);
sub.bind("tcp://*:4001");
sub.subscribe("".getBytes());
sub.setReceiveTimeOut(100);
sleep(1000);
int i = 100_000;
while (i > 0) {
pub.send("1".getBytes(), 0);
i--;
}
pub.close();
sleep(1000);
int k = 0;
while (sub.recv() != null) {
k++;
}
sub.close();
System.out.println("---");
System.out.println(k);
System.out.println("---");
context.term();
}
}
--
Compiling and running the above code on my machine will print:
---
0
---
So there is apparently no message going through. This is one of the surprising
behavior: no message seems to go through a pub/sub socket pair if the publisher
connects. This holds if we reverse the socket creations (i.e. if the subscriber
binds before the publisher connects). If the publisher binds and the subscriber
connects, in both possible orderings, the code prints:
---
60000
---
The second surprising behavior concerns the high water marks. I have seen
nothing in the documentation that suggests the behavior we are seeing, although
I must admit I did not read all of it. Here's what we observe while fiddling
with the above code (with the publisher binding) :
* The sub socket hwm seems to have no effect whatsoever.
* For the hwm of the pub socket to have any effect, it must be set before the
socket binds.
I'm pretty sure the bind/connect asymmetry is not the expected behavior. I'm
much less definitive about the high water marks, but I thought I'd also mention
it.
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