Each thread/fiber/promise is identified by a unique ID.

mint_id () is a fresh unique id.

log msg attaches text msg to the current fiber.

name id label sets label as the name for id.

with_span op fn runs fn (), labelling the timespan during which it runs with op.

suspend_fiber op records that the current fiber is now suspended waiting for op.

create_fiber ~cc id records the creation of fiber id in context cc.

create_cc id ty records the creation of cancellation context id.

create_obj id ty records the creation of id.

get src records reading a promise, taking from a stream, taking a lock, etc.

try_get src records that the current fiber wants to get from src (which is not currently ready).

put dst records resolving a promise, adding to a stream, releasing a lock, etc.

fiber id records that id is now the current fiber for this domain.

suspend_domain records when the event loop is stopped waiting for events from the OS.

domain_spawn ~parent records that the current domain was spawned by fiber parent.

exit_cc () records that the current CC has finished.

exit_fiber id records that fiber id has finished.

error id exn records that id received an error.