ZeroMQ

Messaging Patterns

Underneath the brown paper wrapping of ØMQ’s socket API lies the world of messaging patterns. If you have a background in enterprise messaging, or know UDP well, these will be vaguely familiar. But to most ØMQ newcomers, they are a surprise because we’re so used to the TCP paradigm where a socket maps one-to-one to another node.

Let’s recap briefly what ØMQ does for you. It delivers blobs of data (messages) to nodes, quickly and efficiently. You can map nodes to threads, processes, or nodes. ØMQ gives your applications a single socket API to work with, no matter what the actual transport is (e.g., in-process, inter-process, TCP, or multicast). It automatically reconnects to peers as they come and go. It queues messages at both sender and receiver, as needed. It manages these queues carefully to ensure processes don’t run out of memory, overflowing to disk when appropriate. It handles socket errors. It does all I/O in background threads. It uses lock-free techniques for talking between nodes, so there are never locks, waits, semaphores, or deadlocks.

But cutting through that, it routes and queues messages according to precise recipes called patterns. It is these patterns that provide ØMQ’s intelligence. They encapsulate our hard-earned experience of the best ways to distribute data and work. ØMQ’s patterns are hard-coded, but future versions may allow user-definable patterns.

ØMQ patterns are implemented by pairs of sockets with matching types. ...