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synced 2025-06-03 18:50:19 +02:00
Add try-push, swap-value API to ephemerons
The former allows for knowing whether a push succeeded or not, which is useful for concurrent hash tables. The latter makes ephemerons mutable, if the embedder wants to use them that way.
This commit is contained in:
parent
c86408a33c
commit
a5c69fb920
7 changed files with 74 additions and 8 deletions
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@ -26,9 +26,17 @@ GC_API_ void gc_ephemeron_init(struct gc_mutator *mut,
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GC_API_ struct gc_ref gc_ephemeron_key(struct gc_ephemeron *ephemeron);
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GC_API_ struct gc_ref gc_ephemeron_value(struct gc_ephemeron *ephemeron);
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GC_API_ struct gc_ref gc_ephemeron_swap_value(struct gc_mutator *mut,
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struct gc_ephemeron *ephemeron,
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struct gc_ref ref);
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GC_API_ struct gc_ephemeron* gc_ephemeron_chain_head(struct gc_ephemeron **loc);
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GC_API_ void gc_ephemeron_chain_push(struct gc_ephemeron **loc,
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struct gc_ephemeron *ephemeron);
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GC_API_ int gc_ephemeron_chain_try_push(struct gc_ephemeron **loc,
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struct gc_ephemeron *ephemeron,
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struct gc_ephemeron **tail);
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GC_API_ struct gc_ephemeron* gc_ephemeron_chain_next(struct gc_ephemeron *ephemeron);
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GC_API_ void gc_ephemeron_mark_dead(struct gc_ephemeron *ephemeron);
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@ -253,6 +253,12 @@ void gc_ephemeron_init(struct gc_mutator *mut, struct gc_ephemeron *ephemeron,
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}
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}
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struct gc_ref gc_ephemeron_swap_value(struct gc_mutator *mut,
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struct gc_ephemeron *e,
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struct gc_ref ref) {
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return gc_ephemeron_swap_value_internal(e, ref);
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}
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int gc_visit_ephemeron_key(struct gc_edge edge, struct gc_heap *heap) {
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// Pretend the key is traced, to avoid adding this ephemeron to the
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// global table.
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@ -47,6 +47,10 @@ GC_INTERNAL void
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gc_sweep_pending_ephemerons(struct gc_pending_ephemerons *state,
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size_t shard, size_t nshards);
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GC_INTERNAL struct gc_ref
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gc_ephemeron_swap_value_internal(struct gc_ephemeron *ephemeron,
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struct gc_ref value);
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GC_INTERNAL void gc_ephemeron_init_internal(struct gc_heap *heap,
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struct gc_ephemeron *ephemeron,
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struct gc_ref key,
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@ -165,19 +165,22 @@
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// Concurrent operations on ephemeron lists
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////////////////////////////////////////////////////////////////////////
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static int
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ephemeron_list_try_push(struct gc_ephemeron **loc,
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struct gc_ephemeron *head,
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struct gc_ephemeron **tail,
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struct gc_ephemeron** (*get_next)(struct gc_ephemeron*)) {
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*get_next(head) = *tail;
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return atomic_compare_exchange_weak(loc, tail, head);
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}
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static void
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ephemeron_list_push(struct gc_ephemeron **loc,
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struct gc_ephemeron *head,
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struct gc_ephemeron** (*get_next)(struct gc_ephemeron*)) {
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struct gc_ephemeron *tail = atomic_load_explicit(loc, memory_order_acquire);
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while (1) {
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// There must be no concurrent readers of HEAD, a precondition that
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// we ensure by only publishing HEAD to LOC at most once per cycle.
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// Therefore we can use a normal store for the tail pointer.
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*get_next(head) = tail;
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if (atomic_compare_exchange_weak(loc, &tail, head))
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break;
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}
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while (!ephemeron_list_try_push(loc, head, &tail, get_next))
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;
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}
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static struct gc_ephemeron*
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@ -274,6 +277,11 @@ void gc_ephemeron_chain_push(struct gc_ephemeron **loc,
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struct gc_ephemeron *e) {
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ephemeron_list_push(loc, e, ephemeron_chain);
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}
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int gc_ephemeron_chain_try_push(struct gc_ephemeron **loc,
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struct gc_ephemeron *e,
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struct gc_ephemeron **tail) {
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return ephemeron_list_try_push(loc, e, tail, ephemeron_chain);
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}
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static struct gc_ephemeron* follow_chain(struct gc_ephemeron **loc) {
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return ephemeron_list_follow(loc, ephemeron_chain, ephemeron_is_not_dead);
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}
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@ -283,6 +291,21 @@ struct gc_ephemeron* gc_ephemeron_chain_head(struct gc_ephemeron **loc) {
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struct gc_ephemeron* gc_ephemeron_chain_next(struct gc_ephemeron *e) {
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return follow_chain(ephemeron_chain(e));
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}
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struct gc_ref gc_ephemeron_swap_value_internal(struct gc_ephemeron *e,
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struct gc_ref ref)
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{
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GC_ASSERT(!gc_ref_is_null(ref));
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uintptr_t prev = atomic_load(&e->value.value);
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do {
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if (!prev)
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break;
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} while (!atomic_compare_exchange_weak(&e->value.value, &prev, ref.value));
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return gc_ref(prev);
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}
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void gc_ephemeron_mark_dead(struct gc_ephemeron *e) {
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atomic_store_explicit(&e->key.value, 0, memory_order_release);
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}
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@ -570,6 +593,9 @@ gc_sweep_pending_ephemerons(struct gc_pending_ephemerons *state,
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void gc_ephemeron_init_internal(struct gc_heap *heap,
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struct gc_ephemeron *ephemeron,
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struct gc_ref key, struct gc_ref value) {
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GC_ASSERT(!gc_ref_is_null(key));
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GC_ASSERT(!gc_ref_is_null(value));
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// Caller responsible for any write barrier, though really the
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// assumption is that the ephemeron is younger than the key and the
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// value.
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@ -1007,6 +1007,14 @@ gc_ephemeron_init(struct gc_mutator *mut, struct gc_ephemeron *ephemeron,
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// key or the value.
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}
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struct gc_ref
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gc_ephemeron_swap_value(struct gc_mutator *mut, struct gc_ephemeron *e,
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struct gc_ref ref) {
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gc_write_barrier(mut, gc_ref_from_heap_object(e), gc_ephemeron_size(),
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gc_ephemeron_value_edge(e), ref);
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return gc_ephemeron_swap_value_internal(e, ref);
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}
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struct gc_pending_ephemerons *
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gc_heap_pending_ephemerons(struct gc_heap *heap) {
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return heap->pending_ephemerons;
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@ -1090,6 +1090,14 @@ void gc_ephemeron_init(struct gc_mutator *mut, struct gc_ephemeron *ephemeron,
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gc_ephemeron_init_internal(mutator_heap(mut), ephemeron, key, value);
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}
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struct gc_ref
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gc_ephemeron_swap_value(struct gc_mutator *mut, struct gc_ephemeron *e,
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struct gc_ref ref) {
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gc_write_barrier(mut, gc_ref_from_heap_object(e), gc_ephemeron_size(),
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gc_ephemeron_value_edge(e), ref);
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return gc_ephemeron_swap_value_internal(e, ref);
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}
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struct gc_pending_ephemerons *gc_heap_pending_ephemerons(struct gc_heap *heap) {
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#if GC_GENERATIONAL
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if (is_minor_collection(heap))
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@ -555,6 +555,12 @@ void gc_ephemeron_init(struct gc_mutator *mut, struct gc_ephemeron *ephemeron,
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gc_ephemeron_init_internal(mutator_heap(mut), ephemeron, key, value);
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}
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struct gc_ref gc_ephemeron_swap_value(struct gc_mutator *mut,
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struct gc_ephemeron *e,
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struct gc_ref ref) {
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return gc_ephemeron_swap_value_internal(e, ref);
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}
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struct gc_finalizer* gc_allocate_finalizer(struct gc_mutator *mut) {
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return gc_allocate(mut, gc_finalizer_size(), GC_ALLOCATION_TAGGED);
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}
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