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Add opt-in MI_SINGLE_THREADED specialization for the free fast path #1322

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Add opt-in MI_SINGLE_THREADED specialization for the free fast path #1322

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7 changes: 7 additions & 0 deletions src/free.c
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Original file line number Diff line number Diff line change
Expand Up @@ -153,7 +153,14 @@ static inline void mi_free_ex(void* p, size_t* usable) mi_attr_noexcept
mi_segment_t* const segment = mi_checked_ptr_segment(p,"mi_free");
if mi_unlikely(segment==NULL) return;

#if defined(MI_SINGLE_THREADED) && (MI_SINGLE_THREADED)
// Single-threaded specialization (ExGen-Malloc, CAL'25): in a program that only ever
// uses mimalloc from one thread, every block is thread-local, so we can skip the
// thread-id TLS read + atomic load + compare on every free.
const bool is_local = true;
#else
const bool is_local = (_mi_prim_thread_id() == mi_atomic_load_relaxed(&segment->thread_id));
#endif
mi_page_t* const page = _mi_segment_page_of(segment, p);
if (usable!=NULL) { *usable = mi_page_usable_block_size(page); }

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