ZIO Peer
Table of Contents
ZIO provides a peering mechanism. The term peer in ZIO has two
applicable meanings. First, as a noun, it describes a mechanism where
ZIO applications can be partners in a network or graph topology (see
also node). Second, as a verb, it describes a mechanism for ZIO
application so see into the ZIO network in order to know things about
other ZIO applications. The peering is based on ZeroMQ's Zyre
technology and presented via zio::Peer.
1 How it works
A zio::Peer instance is created with a nickname and a set of headers
each of which a key/value pair of strings. Each key must be unique in
the set of headers. After construction, this information is made
available to all other accessible peers and likewise they are known to
the peer that was just constructed. The nickname of a peer is not
required to be unique in the ZIO network but each peer has a unique id
(UUID) to which the nickname and headers are associated.
As peers come and go from the network each peer maintains this
association and its owning application may query it at any time. The
zio::Peer::peers() method will return the UUIDs of all known peers and
with a UUID the zio::Peer::peer_info(uuid) method will return the
nickname and all headers of a peer.
In addition to knowing about a peer, it is common to need to
synchronize between peers. A common synchronization pattern is for
one peer to wait for another to exist on the network. The
zio::Peer::waitfor(nickname) method provides this synchronization.
The method returns only when peer of the given nickname is seen (or a
configurable timeout is reached). The UUIDs of all peers with the
matching nickname are returned.
Another synchronization patter is to do the opposite and wait until a
peer is gone from the network. The zio::Peer::waituntil(uuid) method
may be used for that.
2 Using zio::Peer
t.b.d.