Hi,
> * SUB sockets default to SUBSCRIBE("") instead of None
This becomes a problem with 3.0 and subscription forwarding. The problem
occurs when you don't want to subscribe to all messages. You open a
socket and unsubscribe from "". However, between the two operations you
can be overloaded by huge amount of irrelevant messages from the publisher.
> * LINGER is a property of the Context, and sets a default value for its
> sockets, which is 0 by default, instead of -1
The problem with default LINGER equal to 0 is that following program
doesn't send any message (the socket is destroyed before connection is
established):
s = zmq_socket (ctx, ZMQ_PUSH);
zmq_connect ("tcp://server0001:5555");
zmq_send (s, "ABC", 3, 0);
zmq_close (s);
That's an extremely unintuitive behaviour.
If default linger time of infinity is causing troubles I would rather
suggest going for something like 1 second.
> czmq has `zctx_destroy()`, which sets LINGER, closes sockets, and
> ultimately terminates the context. PyZMQ has *similar* behavior in
> Context.destroy(), where setting LINGER before closing is an optional
> argument, and does not happen by default.
First, let me explain why libzmq doesn't do this kind of thing.
As can be seen from czmq this functionality can only be implemented when
the library either assumes that sockets are never migrated between
threads or that migration is announced to the library in an explicit
manner (calling a function or similar).
This is not case for libzmq. For example, when using Java binding, Java
virtual machine can choose to migrate the socket object to the gc thread
without notifying libzmq about the fact.
Second, the lesson for individual bindings: You can implement this
functionality only if the binding has full control of the threading,
i.e. when you can keep the list of sockets owned by the particular
thread and the language runtime cannot move the sockets to different
threads thus rendering your per-thread socket lists invalid.
Martin
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