Revision 96b96c8d5195b968656e786ded8f6a1a96168427 authored by Jishnu Bhattacharya on 20 March 2024, 18:20:09 UTC, committed by Jishnu Bhattacharya on 20 March 2024, 18:20:09 UTC
1 parent bc7ba3d
work-stealing-queue.h
// This file is a part of Julia. License is MIT: https://julialang.org/license
#ifndef WORK_STEALING_QUEUE_H
#define WORK_STEALING_QUEUE_H
#include <stdalign.h>
#include "julia_atomics.h"
#include "assert.h"
#ifdef __cplusplus
extern "C" {
#endif
// =======
// Chase and Lev's work-stealing queue, optimized for
// weak memory models by Le et al.
//
// * Chase D., Lev Y. Dynamic Circular Work-Stealing queue
// * Le N. M. et al. Correct and Efficient Work-Stealing for
// Weak Memory Models
// =======
typedef struct {
char *buffer;
int32_t capacity;
int32_t mask;
} ws_array_t;
static inline ws_array_t *create_ws_array(size_t capacity, int32_t eltsz) JL_NOTSAFEPOINT
{
ws_array_t *a = (ws_array_t *)malloc_s(sizeof(ws_array_t));
a->buffer = (char *)malloc_s(capacity * eltsz);
a->capacity = capacity;
a->mask = capacity - 1;
return a;
}
static inline void free_ws_array(ws_array_t *a)
{
free(a->buffer);
free(a);
}
typedef struct {
// align to JL_CACHE_BYTE_ALIGNMENT
alignas(JL_CACHE_BYTE_ALIGNMENT) _Atomic(int64_t) top;
alignas(JL_CACHE_BYTE_ALIGNMENT) _Atomic(int64_t) bottom;
alignas(JL_CACHE_BYTE_ALIGNMENT) _Atomic(ws_array_t *) array;
} ws_queue_t;
static inline ws_array_t *ws_queue_push(ws_queue_t *q, void *elt, int32_t eltsz) JL_NOTSAFEPOINT
{
int64_t b = jl_atomic_load_relaxed(&q->bottom);
int64_t t = jl_atomic_load_acquire(&q->top);
ws_array_t *ary = jl_atomic_load_relaxed(&q->array);
ws_array_t *old_ary = NULL;
if (__unlikely(b - t > ary->capacity - 1)) {
ws_array_t *new_ary = create_ws_array(2 * ary->capacity, eltsz);
for (int i = 0; i < ary->capacity; i++) {
memcpy(new_ary->buffer + ((t + i) & new_ary->mask) * eltsz, ary->buffer + ((t + i) & ary->mask) * eltsz, eltsz);
}
jl_atomic_store_release(&q->array, new_ary);
old_ary = ary;
ary = new_ary;
}
memcpy(ary->buffer + (b & ary->mask) * eltsz, elt, eltsz);
jl_fence_release();
jl_atomic_store_relaxed(&q->bottom, b + 1);
return old_ary;
}
static inline void ws_queue_pop(ws_queue_t *q, void *dest, int32_t eltsz) JL_NOTSAFEPOINT
{
int64_t b = jl_atomic_load_relaxed(&q->bottom) - 1;
ws_array_t *ary = jl_atomic_load_relaxed(&q->array);
jl_atomic_store_relaxed(&q->bottom, b);
jl_fence();
int64_t t = jl_atomic_load_relaxed(&q->top);
if (__likely(t <= b)) {
memcpy(dest, ary->buffer + (b & ary->mask) * eltsz, eltsz);
if (t == b) {
if (!jl_atomic_cmpswap(&q->top, &t, t + 1))
memset(dest, 0, eltsz);
jl_atomic_store_relaxed(&q->bottom, b + 1);
}
}
else {
memset(dest, 0, eltsz);
jl_atomic_store_relaxed(&q->bottom, b + 1);
}
}
static inline void ws_queue_steal_from(ws_queue_t *q, void *dest, int32_t eltsz) JL_NOTSAFEPOINT
{
int64_t t = jl_atomic_load_acquire(&q->top);
jl_fence();
int64_t b = jl_atomic_load_acquire(&q->bottom);
if (t < b) {
ws_array_t *ary = jl_atomic_load_relaxed(&q->array);
memcpy(dest, ary->buffer + (t & ary->mask) * eltsz, eltsz);
if (!jl_atomic_cmpswap(&q->top, &t, t + 1))
memset(dest, 0, eltsz);
}
}
#ifdef __cplusplus
}
#endif
#endif
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