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deal with remaining race conditions in these APIs
The jl_live_tasks API now reports all threads, instead of only Tasks first started by the current thread. There is a new abstraction called mtarraylist with adds functionality to small_arraylist (it is layout-compatible). In particular, it makes it safe for another thread to observe the content of the list concurrently with any mutations.
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,81 @@ | ||
| // This file is a part of Julia. License is MIT: https://julialang.org/license | ||
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| #include "julia.h" | ||
| #include "julia_internal.h" | ||
| #include "julia_assert.h" | ||
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| #ifdef __cplusplus | ||
| extern "C" { | ||
| #endif | ||
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| // this file provides some alternate API functions for small_arraylist (push and add) | ||
| // which can be safely observed from other threads concurrently | ||
| // there is only permitted to be a single writer thread (or a mutex) | ||
| // but there can be any number of observers | ||
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| typedef struct { | ||
| _Atomic(uint32_t) len; | ||
| uint32_t max; | ||
| _Atomic(_Atomic(void*)*) items; | ||
| _Atomic(void*) _space[SMALL_AL_N_INLINE]; | ||
| } small_mtarraylist_t; | ||
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| // change capacity to at least newlen | ||
| static void mtarraylist_resizeto(small_mtarraylist_t *a, size_t len, size_t newlen) JL_NOTSAFEPOINT | ||
| { | ||
| size_t max = a->max; | ||
| if (newlen > max) { | ||
| size_t nm = max * 2; | ||
| if (nm == 0) | ||
| nm = 1; | ||
| while (newlen > nm) | ||
| nm *= 2; | ||
| void *olditems = (void*)jl_atomic_load_relaxed(&a->items); | ||
| void *p = calloc_s(nm * sizeof(void*)); | ||
| memcpy(p, olditems, len * sizeof(void*)); | ||
| jl_atomic_store_release(&a->items, (_Atomic(void*)*)p); | ||
| a->max = nm; | ||
| if (olditems != (void*)&a->_space[0]) { | ||
| jl_task_t *ct = jl_current_task; | ||
| jl_gc_add_quiescent(ct->ptls, (void**)olditems, free); | ||
| } | ||
| } | ||
| } | ||
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| // single-threaded | ||
| void mtarraylist_push(small_arraylist_t *_a, void *elt) | ||
| { | ||
| small_mtarraylist_t *a = (small_mtarraylist_t*)_a; | ||
| size_t len = jl_atomic_load_relaxed(&a->len); | ||
| mtarraylist_resizeto(a, len, len + 1); | ||
| jl_atomic_store_release(&jl_atomic_load_relaxed(&a->items)[len], elt); | ||
| jl_atomic_store_release(&a->len, len + 1); | ||
| } | ||
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| // single-threaded | ||
| void mtarraylist_add(small_arraylist_t *_a, void *elt, size_t idx) | ||
| { | ||
| small_mtarraylist_t *a = (small_mtarraylist_t*)_a; | ||
| size_t len = jl_atomic_load_relaxed(&a->len); | ||
| mtarraylist_resizeto(a, len, idx + 1); | ||
| jl_atomic_store_release(&jl_atomic_load_relaxed(&a->items)[idx], elt); | ||
| if (jl_atomic_load_relaxed(&a->len) < idx + 1) | ||
| jl_atomic_store_release(&a->len, idx + 1); | ||
| } | ||
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| // concurrent-safe | ||
| size_t mtarraylist_length(small_arraylist_t *_a) | ||
| { | ||
| small_mtarraylist_t *a = (small_mtarraylist_t*)_a; | ||
| return jl_atomic_load_relaxed(&a->len); | ||
| } | ||
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| // concurrent-safe | ||
| void *mtarraylist_get(small_arraylist_t *_a, size_t idx) | ||
| { | ||
| small_mtarraylist_t *a = (small_mtarraylist_t*)_a; | ||
| size_t len = jl_atomic_load_acquire(&a->len); | ||
| if (idx >= len) | ||
| return NULL; | ||
| return jl_atomic_load_relaxed(&jl_atomic_load_relaxed(&a->items)[idx]); | ||
| } |
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