epics-libcom-rs 0.25.0

EPICS libCom for Rust — task seam, thread priority bands, errlog, environment and time primitives, and the protocols' shared socket layer
Documentation

epics-libcom-rs

EPICS libCom for Rust: the layer an IOC is built on, with no record system above it. Two modules, named for the two halves of C's libCom they port:

module C counterpart what it is
runtime epicsThread, epicsTime, errlog, envDefs, epicsString the task spawn/sleep/interval seam and its two backends, EPICS priority bands, the general-time provider, the environment-parameter table, errlog
net osiSock the EPICS protocols' shared socket layer — per-NIC async UDP with TX/RX accuracy, interface enumeration, loopback multicast

It exists so a consumer that wants the concurrency and socket primitives — a protocol client, a gateway, pvxs-rs — does not have to take the database with them (issue #55).

You usually do not depend on this crate directly. epics-base-rs re-exports both modules at their original paths, so epics_base_rs::runtime::… and epics_base_rs::net::… still resolve exactly as before; the split changed no call site anywhere in the workspace. Depend on epics-libcom-rs only when you want the layer without epics-base-rs.

The two task backends

runtime::task's spawn/sleep/interval seam has two mutually exclusive backends, selected by build.rs into one cfg so the ~two dozen seam sites gate on a single uniform condition:

  • tokio_backend — the tokio runtime. The hosted default; you get this with no flags.
  • exec_backend — the std-thread background executor (callback pool + delayed timer + scanOnce worker). Unconditional on armv7-rtems-eabihf, which has no tokio reactor.

EXEC_BACKEND states which one a given build got, so a crate above can pin its own copy of the predicate to it with a const _: () = assert!(…) — epics-base-rs does exactly that.

Feature levers

feature what it does
rtems-exec-model select exec_backend on a hosted target. For a Linux (e.g. PREEMPT_RT) blocking-front-end deployment that wants the same runtime-free spawn/timer backend the RTEMS build uses, driving async record-processing completion on dedicated OS threads instead of a tokio runtime. Off by default; the hosted default is byte-identical without it.
linux-rt back runtime::sync::PriorityInheritanceMutex with a pthread_mutex_t carrying PTHREAD_PRIO_INHERIT (epics-base 7-E 5a8b6e41). No-op off Linux. Only enable where threads run SCHED_FIFO/SCHED_RR and unbounded priority inversion is a real risk.

Both are forwarded by epics-base-rs, so --features epics-base-rs/linux-rt and --features epics-base-rs/rtems-exec-model mean what they always did.

RTEMS

The net module's socket-bearing submodules (async_udp_v4, iface_map, loopback_mcast) are host-only — socket2/if-addrs do not build for armv7-rtems-eabihf, and the RTEMS CA server uses the separate raw-libc socket driver. The wire constants beside them stay on every target, because the PVA SEARCH decoder has to embed them on RTEMS too.

./scripts/rtems-check.sh compiles this crate for the target in both build configurations.