Removal of ZMQ_IDENTITY resulted in various session classes doing
almost the same thing. This patch merges the classes into a single
class.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

This patch simplifies the whole codebase significantly,
including dropping depedency on libuuid.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

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

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

Bug in previous refactoring fixed.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Till now the code was spread over mutliple locations.
Additionally, the code was made more formally correct,
with explicit pipe state machine etc.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

So far, there was a pair of unidirectional pipes between a socket
and a session (or an inproc peer). This resulted in complex
problems with half-closed states and tracking which inpipe
corresponds to which outpipe.

This patch doesn't add any functionality in itself, but is
essential for further work on features like subscription
forwarding.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

This patch addresses serveral issues:
1. It gathers message related functionality scattered over whole
   codebase into a single class.
2. It makes zmq_msg_t an opaque datatype. Internals of the class
   don't pollute zmq.h header file.
3. zmq_msg_t size decreases from 48 to 32 bytes. That saves ~33%
   of memory in scenarios with large amount of small messages.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

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

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

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

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

    1. ZMQ_LINGER option can be set/get
    2. options are part of own_t base class rather than being declared
       separately by individual objects
    3. Linger option is propagated with "term" command so that the
       newest value of it is used rather than the stored old one.
    4. Session sets the linger timer if needed and terminates
       as soon as it expires.
    5. Corresponding documentation updated.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Session base class now handles the engine events exclusively. It notifies
derived session types using dedicated "attached" and "detached" events.

Couple of bugs was fixed along the way.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

When a session is being closed down its inbound and outbound
pipe pointers are set to null. If (re) connection happens at
that time, session may try to reinistantiate the pipes which
is wrong. This patch allows session to attach pipes only once
in its lifetime.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Specifically, shutdown of child objects is initiated *before* termination
handshake with socket object.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Sockets may now be migrated between OS threads; sockets may not be used by
more than one thread at any time. To migrate a socket to another thread the
caller must ensure that a full memory barrier is called before using the
socket from the target thread.

The new zmq_close() semantics implement the behaviour discussed at:

http://lists.zeromq.org/pipermail/zeromq-dev/2010-July/004244.html

Specifically, zmq_close() is now deterministic and while it still returns
immediately, it does not discard any data that may still be queued for
sending. Further, zmq_term() will now block until all outstanding data has
been sent.

TODO: Many bugs have been introduced, needs testing. Further, SO_LINGER or
an equivalent mechanism (possibly a configurable timeout to zmq_term())
needs to be implemented.

This commit introduces the necessary changes necessary
for implementing flow control. None of the socket types
implements the flow control yet. The code will crash when
the flow control is enabled and the thw lwm is reached.

The following commits will add flow-control support for
individual socket types.