ZIO Node
Table of Contents
A zio::Node represents one vertex a graph or network which is
connected to other ZIO applications (which themselves may utilize
zio::Node) by the ZIO messages they exchange. In general, this ZIO
graph is directed (possibly bidirectional) and possibly cyclic. When
zio::Node is used, the network may be considered a specialized ported
graph. That is, a ZIO node has a set of "ports" each of which are
identified by a name unique to the node and each have a ZeroMQ socket
through which messages are passed.
A zio::Node as a zio::Peer (see peer) and uses it to advertise headers
holding the addresses of any ports (zio::Port, see port) which have
been asked to bind(). This allows other ZIO nodes (or in general
other ZIO peers) to know an address to use to connect(). It thus
allows edges to be formed in the graph based on specifying
application-dependent abstract addressing which is not tied to
specific transport or hardware.
For example, some data source may be partitioned and access may be
distributed across a set of nodes (eg, as in some DAQ layer or across
various points of the Wire-Cell execution graph). These nodes may
each bind() and advertise the relevant address associated with a
nickname or headers following some convention. Another set of nodes
knowing this convention may be configured connect() to addresses found
by some match on the advertised information. This allows the graph to
self-organize without the human specifying detailed absolute
addressing. It also allows the graph to self-heal as nodes die and
are reborn on different physical addresses but retain their nickname
and headers.
1 Using zio::Node
A node carries the nickname and origin value. The nickname is advertised by the node's peer and the origin is provided by all messages produced by the node's ports.
zio::Node node("mynode", 42);
A ZIO application using a node will populate its ports as needed specifying their name and ZeroMQ port type. This information will be automatically provided by peer discovery.
auto input = node.port("input", ZMQ_SUB); auto output = node.port("output", ZMQ_PUB);
After population, ports can be accessed by name.
auto ip = node.port("input"); auto op = node.port("output");
See port for details on using ports. Once port operations are complete the node may go online.
node.online();
This triggers any port binding, peer advertising of node nickname, related port address headers, and any extra headers provided to the node by the application and finally any port connections including indirect ones that rely on peer discovery.
Later a node may be explicitly taken offline:
node.offline();
This will disconnect and unbind ports and destroy the node's peer object removing it from the ZIO discovery network. The node itself retains all ports and the above state changes transition can be repeated:
node.online();