Solution: signal error to caller, and apply appropriate cleanup

Solution: replace by "routing id"

Solution: replace by "routing id"

Solution: add initial implementation

Solution: extract as_socket_base_t function

Solution: added test case (with dummy implementation of zmq_socket_get_peer_state)

Solution: replace ETIMEDOUT within socket_poller_t and all client code by EAGAIN

Fixes #2713

Solution: Return EBADF instead

Problem: calling zmq_poller_wait* with NULL events causes an assertion, as opposed to other NULL arguments, which return an error

Solution: return EFAULT when such an operation is attempted

Solution: add checks, added test cases

solution: fix it

In particular, on Windows, using FD_ZERO is much more efficient than
zeroing out the whole structure.

Problem: FD set copying on Windows still not optimal on some places. Solution: Improved memcpy() of FD sets for Windows builds.

Unnecessary dynamic memory allocation for zmq::socket_poller_t in zmq_poller_poll(). Fixed by allocating zmq::socket_poller_t from stack.

Solution: Pass (std::nothrow) as done in all other places.

As discussed in #2307

Solution: fix the check for the socket.
This regression happens when using zloop with zmq_pollitem_it with
only file descriptors registerted through zloop_poller.

item.fd should be ignored if item.socket is defined.

Failing to check .socket could cause false-matches, raising EINVAL in zmq_poller_modify_fd.

This block of code will either return -1 or fall through.
The while (true) does nothing.
The braces limit the scope of int rc.

Solution: honor it

* Doing so was zmq_poller_poll to always return 0.

This should restore full compatibility with earlier zmq_poll behavior.

It complicates things a little bit, as collisions must be detected, and when collisions are found:

- event masks must be merged
- pollitems, events arrays are no longer co-ordered

Reverts the recent zmq_proxy patch to workaround the lack of repeat-item support in zmq_poll that is now fixed.

not -1, ETIMEDOUT like zmq_poller

Return value is the number of events found. This also propagates to the return value of zmq_poller_wait_all.

zmq_poller_wait was only returning events on the first-registered socket.

variable-size array allocation is not allowed by some compilers

enables zmq_poll on threadsafe sockets only supported in zmq_poller (radio, dish, etc.)

instead of allocating a new, identical array and copying the data.

This is only safe while zmq_poller_event_t and zmq::socket_poller_t::event_t are the same struct,
which they presumably will remain.

avoids unnecessary heap allocations, races on the number of items

Solution: zmq_poller_wait_all signals all events

allows signaling multiple events with one call to zmq_poller_wait_all
rather than emitting only one event.

this prepares for zmq_poll being based on zmq_poller,
which requires events for all sockets rather than just one.

Solution: Provide poll() for Windows as well. This is a build option that
defaults to off as the resulting binary will only run on Windows Vista or
newer.

This is not tested with alternative Winsock service providers like VMCI,
but the documentation for WSAPoll does not mention limitations.

On my local machine, throughput improves by ~10 % (20 simultaneous
remote_thr workes to one local_thr, 10 byte messages), while latency
improves by ~30 % (measured with remote/local_lat).

Solution:
- Add checks for **poller_p_ to ensure that we do not segfault when either it
  or the value within it are NULL
- Add tests for the above and increase error state coverage

Solution:
Wrap and clean it.

Solution:
- Add check for the [count] parameter in zmq_sendiov() and zmq_recviov()
- Use and add test for zmq_sendiov() in tests/test_iov.cpp
- Add error state tests for zmq_sendiov() in tests/test_iov.cpp
- Add error state tests for zmq_recviov() in tests/test_iov.cpp
- Cleanup tests/test_iov.cpp for style, consistency and clarity
- Generally improve test coverage for both API methods

Hat-tip:
@somdoron, @bluca

Solution: fix it

Solution: use zmq_assert to ensure it's not a nullpointer

Solution: fix it