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feat(stack,runtime): per-shape actor stacks — Stack::new(reserve, guard), Config knobs, pool rule (RFC 019 §1)

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Stack takes an explicit (reserve, guard) shape, both page-rounded and
stored; usable_base derives from the stored guard. Guard default raised
4 KiB -> 64 KiB (DEFAULT_STACK_GUARD): probestack makes one page enough
for Rust frames, but an unprobed C frame can leap a page in one sub rsp
— the motivating SQLite segfault. Reserve default stays 64 KiB
(DEFAULT_STACK_RESERVE); ACTOR_STACK_SIZE retired.

Config::{stack_reserve, stack_guard} thread the runtime defaults into
RuntimeInner pre-rounded. All acquisition/recycling now goes through
acquire_stack/recycle_stack carrying the pool rule: only default-shaped
stacks are pooled (pooled ⇒ default-shaped by induction); custom shapes
mmap fresh and munmap at death. Pool lock still dropped before any mmap.

No public spawn API change (SpawnOpts is the next commit).

Tests: shape rounding + accessors, wide-guard faults at both ends
(subprocess), Config::stack_reserve permits >64 KiB recursion that
previously could only segfault.
This commit is contained in:
Claude (sandbox)
2026-08-08 14:18:27 +00:00
parent a03a7ca01e
commit 0fe052bc7e
7 changed files with 254 additions and 46 deletions
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tests/context.rs
+5 -5
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@@ -23,7 +23,7 @@ extern "C-unwind" fn actor_simple() {
#[test]
fn actor_runs_and_returns_to_scheduler() {
reset_log();
let stack = Stack::new(64 * 1024).unwrap();
let stack = Stack::new(64 * 1024, 4096).unwrap();
let sp = init_actor_stack(stack.top(), actor_simple);
set_actor_sp(sp);
unsafe { switch_to_actor() };
@@ -40,7 +40,7 @@ extern "C-unwind" fn actor_two_steps() {
#[test]
fn actor_yields_and_resumes() {
reset_log();
let stack = Stack::new(64 * 1024).unwrap();
let stack = Stack::new(64 * 1024, 4096).unwrap();
let sp = init_actor_stack(stack.top(), actor_two_steps);
set_actor_sp(sp);
@@ -85,7 +85,7 @@ extern "C-unwind" fn actor_reg_check() {
#[test]
fn callee_saved_registers_survive_yield() {
let stack = Stack::new(64 * 1024).unwrap();
let stack = Stack::new(64 * 1024, 4096).unwrap();
let sp = init_actor_stack(stack.top(), actor_reg_check);
set_actor_sp(sp);
unsafe { switch_to_actor(); switch_to_actor(); }
@@ -117,8 +117,8 @@ extern "C-unwind" fn actor_b() {
#[test]
fn two_actors_dont_corrupt_each_other() {
let stack_a = Stack::new(64 * 1024).unwrap();
let stack_b = Stack::new(64 * 1024).unwrap();
let stack_a = Stack::new(64 * 1024, 4096).unwrap();
let stack_b = Stack::new(64 * 1024, 4096).unwrap();
let sp_a = init_actor_stack(stack_a.top(), actor_a);
let sp_b = init_actor_stack(stack_b.top(), actor_b);