Trace Task Lifecycle Events

Registers a hook on a pool handle. The hook is called as fn(event, id) at each task lifecycle event that this process observes:

Usage

mizu_pool_trace(pool, fn = NULL)

Arguments

pool

a pool handle from mizu_pool() or mizu_pool_attach(); inside a task, the evaluating worker's own handle from mizu_current_pool().

fn

a function(event, id), or NULL to remove a registered hook.

Value

Invisibly, NULL.

Details

• "submit" when a task is committed.

• On worker handles: "start" before the evaluation of a task, and "done" or "error" when its result is published.

• "drop" when a claimed task is discarded (cancelled before or during execution, or its out-of-line payload died with its enqueuer).

• "rehome" when a doorbell help beat claims a map runner. The helper moves it onto its own deque — where idle peers can steal it — instead of executing it nested.

id identifies the task as "<submitter slot>:<counter>". This id is stable across processes, so logs from both sides of a pool can be correlated.

Registration is per-handle and per-process. A submitter that traces its own handle sees only "submit". Execution events happen on the workers. To trace a worker, install the hook from a task on the worker's own handle: mizu_submit(p, mizu_pool_trace(mizu_current_pool(), fn)). The disabled hook costs one pointer check per event site, and no event sites exist on the channel hot path. An error raised by the hook propagates as an infrastructure failure at its site. On a worker, it takes the worker down. This differs from the own error of a task, which is published as the ERR result of that task.

Examples

p <- mizu_pool()
mizu_pool_trace(p, function(event, id) cat(event, id, "\n"))
t <- mizu_submit(p, 1 + 1)
#> submit 0:1 
mizu_collect(t)
#> [1] 2
mizu_pool_trace(p)
mizu_pool_stop(p)