This bug caused signal during blocking call to assert.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Storing commands in OS socket buffers caused whole lot of
problems when free space in the buffer ran out. This patch
stores commands in ypipes instead and uses socketpair just
to signal the other thread, ie. at most one byte is stored
in the socketpair at any single instant.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

For the platforms that don't support MSG_DONTWAIT the reader
socket in mailbox_t was kept in non-blocking state and flipped
to blocking state and back when blocking read was requested.
Now, the state is preserved between calls and flipped only
if different type of operation (block vs. non-block) is
requested.
Signed-off-by: Fabien Ninoles <fabien@tzone.org>
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

- Add doc and tests
- Add options and setup
- Wait using poll/select
Signed-off-by: Fabien Ninoles <fabien@tzone.org>
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

For historical reasons queue to transfer commands between
threads was called 'signaler'. Given that it was used to
pass commands rather than signals it was renamed to 'mailbox',
see Erlang mailboxes.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

If the socketpair used by signaler_t fills up, this can lead to deadlock.
This patch provides partial resolution by attempting to resize SO_SNDBUF on
the writer side, and if that fails we shall at least assert rather than
hang.

I've also refactored the signaler_t code to make the platform-dependent
parts clearer and have tested both the MSG_DONTWAIT and standard POSIX path
in recv.

The Win32 implementation currently does not implement resizing as I'm not
convinced that it's safe, but it will also assert like other platforms if
signaler_t::send() cannot succeed.

The OpenVMS implementation has been carried forward but is untested.
Signed-off-by: Martin Lucina <mato@kotelna.sk>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Add signaler_sndbuf_size option to config.hpp which allows the user to
increase the size of the send buffer used by the signalling socketpair.

Implement random backoff for reconnection attempts using a primitive
pseudo-random generation to prevent reconnection storms.

Add wait_before_connect option to config.hpp to allow the user to enable
random delay even on initial connect. Default is false for low latency.
Signed-off-by: Martin Lucina <mato@kotelna.sk>

This patch restarts the send() or recv() inside zmq::signaler_t if the call fails
due to EINTR.