Default Child Process Launcher

Returns the launcher that mizu_channel(), mizu_pool() and mizu_spawn_workers() use unless given a custom one. It spawns a detached child R process through a static Rscript runner, with the entry expression and the .libPaths() of the host hex-encoded in argv.

Usage

mizu_launcher(stdout = "", stderr = "")

Arguments

stdout, stderr

forwarded to system2(). The default "" sends the child output (for a channel peer, including its error epilogue) to the console of the host, FALSE discards it, and a file name collects it in that file.

On Windows, the child holds a redirection file without sharing for its lifetime. Only one live process can use a file at a time. Other processes cannot read the file while the child lives. A second spawn with the same file fails to launch. In a pool, this failure causes a startup timeout. A custom launcher that sets the file name from slot gives one log file per worker (see examples).

Value

A function(token, slot). mizu_pool() and mizu_spawn_workers() call it with both arguments to spawn the worker for slot. mizu_channel() calls it with token alone to spawn the peer.

Containers

system2(wait = FALSE) detaches background children, so workers and peers are adopted by PID 1 of the process namespace and reaped by that init when they exit. In a container whose PID 1 does not reap (a plain docker run without --init), exited children accumulate as zombie PID-table entries. This is harmless to mizu itself — death verdicts come from the liveness lock, never the PID — but PID-probe supervision misreads zombies as alive, and mizu_prune() cannot reclaim a dead process's regions while its PID stays taken.

Examples

# One log file per worker on Windows.
launcher <- function(token, slot) {
  f <- if (missing(slot)) "peer.log" else sprintf("worker-%d.log", slot)
  mizu_launcher(stderr = f)(token, slot)
}