InProc

Inproc, short for in-process transport, is a messaging mechanism used to enable fast communication between threads within a single process. It is designed to avoid kernel or network overhead by routing messages entirely inside the process, usually via in-memory data structures and synchronization primitives.

The most prominent example is its use in ZeroMQ, where inproc endpoints are represented as inproc://name. A socket can bind to such an endpoint and other sockets can connect to the same endpoint. All participants must reside in the same process and typically within the same library context. The inproc transport offers very low latency and high throughput because there is no inter-process or network stack involved. It supports the same messaging patterns as other ZeroMQ transports, such as REQ/REP, PUB/SUB, PUSH/PULL, and ROUTER/DEALER, subject to the library’s implementation details.

Practical use cases include building internal pipelines between a frontend and a worker pool, coordinating tasks among threads, or implementing internal routing and fan-out within a single application. It is especially useful for modular designs where components communicate via well-defined sockets without exposing the communication to the outside world.

Limitations of inproc include its confinement to a single process; it cannot be used for inter-process communication. Endpoints are bound and connected within the same process lifetime, and there is no persistence or durability. For cross-process needs, other transports such as ipc (Unix-domain sockets) or tcp are used.