[pull] master from ruby:master - #1340
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`st_replace` assumes that the `st_table` hasn't been initialized, so when duping a hash, we shouldn't pre-allocate the `st_table` otherwise we'll leak memory.
thread_sched_setup_running_threads runs on every context switch (park,
resume, and both ends of every blocking region) and took the global
ractor.sched.lock to maintain the running_threads and timeslice lists
and running_cnt. With many ractors switching concurrently this lock is
the scaling ceiling.
Replace all three with ntlist, a per-location registration of who runs
where, and no shared counter:
- a thread on a shared nt registers in that nt's running_th, under the
nt's own lock -- uncontended, no cross-core traffic
- a dedicated nt goes on ntlist.running_dnts while its thread runs (the
switch rate of dedicated threads is what it always was; only the lock
shrank), so the fast path writes no shared cache line at all
The consumers walk the registrations: the barrier's interrupt walk also
counts them into a snapshot (barrier_running_cnt) and stamps each nt
with the barrier serial; a stamped nt deregistering during that barrier
decrements the snapshot under sched.lock, so the completion check stays
O(1) however many runners there are.
The timeslice list becomes timeslice.scheds, the scheds whose readyq
holds waiters. The enq that fills an empty readyq (and the add path
taking a turn with waiters already queued) links the sched; the timer
thread interrupts each listed sched's running thread and prunes entries
whose readyq drained. A steadily contended sched stays linked, so the
switch path never touches the list, and idle scheds are not walked at
all. The timer takes each sched's lock by trylock, because the
switchers nest sched.lock -> timeslice.lock; pruning is lazy, so
ractor_free delists the dying ractor's sched.
Barrier pairing needs no fences: the barrier sets barrier_is_waiting
and then walks the registrations under their locks; a switch moves its
registration under the same lock and then reads the flag. A walk that
missed a registration ran before that registration's critical section,
so its flag store is visible to that switcher. Nothing may start
running while the flag stands -- an interrupt flag alone would let a
resuming thread run, and allocate, inside the stop-the-world section --
so the add path takes its registration back and waits for
rb_ractor_sched_barrier_end's broadcast. While a scan holds a
running_th lock the registered thread cannot finish parking, so it
cannot die under the scan. An snt turned dedicated under
rb_thread_lock_native_thread has no creation-time running_thread, so
the running_dnts registration writes nt->running_thread itself.
R ractor pairs ping-ponging via ports (msgs/sec) and R ractors doing
pipe write/read round-trips (rt/sec), 16-HT machine (Ryzen 9 5900HX),
mean of 2 alternating same-tree runs:
before after
port pairs 8 503k 815k +62%
port pairs 32 453k 799k +76%
pipe self 4R 837k 940k +12%
pipe self 16R 820k 898k +10%
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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