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strengthen some atomic operations for weak memory models

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This commit is contained in:
daan 2019-08-26 08:11:15 -07:00
parent 2159c22415
commit 5c7c106d62
4 changed files with 53 additions and 34 deletions
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45
include/mimalloc-atomic.h
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@ -30,26 +30,32 @@ terms of the MIT license. A copy of the license can be found in the file
// ------------------------------------------------------
// Atomically add a 64-bit value; returns the previous value.
// Note: not using _Atomic(int64_t) as it is only used for stats.
static inline int64_t mi_atomic_add64(volatile int64_t* p, int64_t add);
// Note: not using _Atomic(int64_t) as it is only used for statistics.
static inline void mi_atomic_add64(volatile int64_t* p, int64_t add);
// Atomically add a value; returns the previous value.
// Atomically add a value; returns the previous value. Memory ordering is relaxed.
static inline intptr_t mi_atomic_add(volatile _Atomic(intptr_t)* p, intptr_t add);
// Atomically compare and exchange a value; returns `true` if successful. May fail spuriously.
// Atomically compare and exchange a value; returns `true` if successful.
// May fail spuriously. Memory ordering as release on success, and relaxed on failure.
// (Note: expected and desired are in opposite order from atomic_compare_exchange)
static inline bool mi_atomic_cas_weak(volatile _Atomic(uintptr_t)* p, uintptr_t desired, uintptr_t expected);
// Atomically compare and exchange a value; returns `true` if successful.
// Memory ordering is acquire-release
// (Note: expected and desired are in opposite order from atomic_compare_exchange)
static inline bool mi_atomic_cas_strong(volatile _Atomic(uintptr_t)* p, uintptr_t desired, uintptr_t expected);
// Atomically exchange a value.
// Atomically exchange a value. Memory ordering is acquire-release.
static inline uintptr_t mi_atomic_exchange(volatile _Atomic(uintptr_t)* p, uintptr_t exchange);
// Atomically read a value
// Atomically read a value. Memory ordering is relaxed.
static inline uintptr_t mi_atomic_read_relaxed(const volatile _Atomic(uintptr_t)* p);
// Atomically write a value
// Atomically read a value. Memory ordering is acquire.
static inline uintptr_t mi_atomic_read(const volatile _Atomic(uintptr_t)* p);
// Atomically write a value. Memory ordering is release.
static inline void mi_atomic_write(volatile _Atomic(uintptr_t)* p, uintptr_t x);
// Yield
@ -76,11 +82,16 @@ static inline uintptr_t mi_atomic_decrement(volatile _Atomic(uintptr_t)* p) {
return mi_atomic_subu(p, 1);
}
// Atomically read a pointer
// Atomically read a pointer; Memory order is relaxed.
static inline void* mi_atomic_read_ptr_relaxed(volatile _Atomic(void*) const * p) {
return (void*)mi_atomic_read_relaxed((const volatile _Atomic(uintptr_t)*)p);
}
// Atomically read a pointer; Memory order is acquire.
static inline void* mi_atomic_read_ptr(volatile _Atomic(void*) const * p) {
return (void*)mi_atomic_read((const volatile _Atomic(uintptr_t)*)p);
}
// Atomically write a pointer
static inline void mi_atomic_write_ptr(volatile _Atomic(void*)* p, void* x) {
mi_atomic_write((volatile _Atomic(uintptr_t)*)p, (uintptr_t)x );
@ -127,18 +138,21 @@ static inline bool mi_atomic_cas_weak(volatile _Atomic(uintptr_t)* p, uintptr_t
static inline uintptr_t mi_atomic_exchange(volatile _Atomic(uintptr_t)* p, uintptr_t exchange) {
return (uintptr_t)RC64(_InterlockedExchange)((volatile msc_intptr_t*)p, (msc_intptr_t)exchange);
}
static inline uintptr_t mi_atomic_read_relaxed(volatile _Atomic(uintptr_t) const* p) {
static inline uintptr_t mi_atomic_read(volatile _Atomic(uintptr_t) const* p) {
return *p;
}
static inline uintptr_t mi_atomic_read_relaxed(volatile _Atomic(uintptr_t) const* p) {
return mi_atomic_read(p);
}
static inline void mi_atomic_write(volatile _Atomic(uintptr_t)* p, uintptr_t x) {
mi_atomic_exchange(p,x);
}
static inline void mi_atomic_yield(void) {
YieldProcessor();
}
static inline int64_t mi_atomic_add64(volatile _Atomic(int64_t)* p, int64_t add) {
static inline void mi_atomic_add64(volatile _Atomic(int64_t)* p, int64_t add) {
#ifdef _WIN64
return mi_atomic_add(p,add);
mi_atomic_add(p,add);
#else
int64_t current;
int64_t sum;
@ -146,7 +160,6 @@ static inline int64_t mi_atomic_add64(volatile _Atomic(int64_t)* p, int64_t add)
current = *p;
sum = current + add;
} while (_InterlockedCompareExchange64(p, sum, current) != current);
return current;
#endif
}
@ -156,9 +169,9 @@ static inline int64_t mi_atomic_add64(volatile _Atomic(int64_t)* p, int64_t add)
#else
#define MI_USING_STD
#endif
static inline int64_t mi_atomic_add64(volatile int64_t* p, int64_t add) {
static inline void mi_atomic_add64(volatile int64_t* p, int64_t add) {
MI_USING_STD
return atomic_fetch_add_explicit((volatile _Atomic(int64_t)*)p, add, memory_order_relaxed);
atomic_fetch_add_explicit((volatile _Atomic(int64_t)*)p, add, memory_order_relaxed);
}
static inline intptr_t mi_atomic_add(volatile _Atomic(intptr_t)* p, intptr_t add) {
MI_USING_STD
@ -180,6 +193,10 @@ static inline uintptr_t mi_atomic_read_relaxed(const volatile _Atomic(uintptr_t)
MI_USING_STD
return atomic_load_explicit((volatile _Atomic(uintptr_t)*) p, memory_order_relaxed);
}
static inline uintptr_t mi_atomic_read(const volatile _Atomic(uintptr_t)* p) {
MI_USING_STD
return atomic_load_explicit((volatile _Atomic(uintptr_t)*) p, memory_order_acquire);
}
static inline void mi_atomic_write(volatile _Atomic(uintptr_t)* p, uintptr_t x) {
MI_USING_STD
return atomic_store_explicit(p, x, memory_order_release);

18
src/alloc.c
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@ -118,22 +118,24 @@ static mi_decl_noinline void _mi_free_block_mt(mi_page_t* page, mi_block_t* bloc
mi_segment_t* segment = _mi_page_segment(page);
if (segment->page_kind==MI_PAGE_HUGE) {
// huge page segments are always abandoned and can be freed immediately
mi_assert_internal(segment->thread_id==0);
mi_assert_internal(segment->abandoned_next==NULL);
mi_assert_internal(mi_atomic_read_relaxed(&segment->thread_id)==0);
mi_assert_internal(mi_atomic_read_ptr_relaxed(mi_atomic_cast(void*,&segment->abandoned_next))==NULL);
// claim it and free
mi_block_set_next(page, block, page->free);
page->free = block;
page->used--;
mi_heap_t* heap = mi_get_default_heap();
segment->thread_id = heap->thread_id;
_mi_segment_page_free(page,true,&heap->tld->segments);
// paranoia: if this it the last reference, the cas should always succeed
if (mi_atomic_cas_strong(&segment->thread_id,heap->thread_id,0)) {
mi_block_set_next(page, block, page->free);
page->free = block;
page->used--;
_mi_segment_page_free(page,true,&heap->tld->segments);
}
return;
}
do {
tfree = page->thread_free;
use_delayed = (mi_tf_delayed(tfree) == MI_USE_DELAYED_FREE ||
(mi_tf_delayed(tfree) == MI_NO_DELAYED_FREE && page->used == page->thread_freed+1)
(mi_tf_delayed(tfree) == MI_NO_DELAYED_FREE && page->used == mi_atomic_read_relaxed(&page->thread_freed)+1) // data-race but ok, just optimizes early release of the page
);
if (mi_unlikely(use_delayed)) {
// unlikely: this only happens on the first concurrent free in a page that is in the full list

20
src/memory.c
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@ -131,7 +131,7 @@ static bool mi_region_commit_blocks(mem_region_t* region, size_t idx, size_t bit
mi_assert_internal(&regions[idx] == region);
// ensure the region is reserved
void* start = mi_atomic_read_ptr_relaxed(&region->start);
void* start = mi_atomic_read_ptr(&region->start);
if (start == NULL)
{
start = _mi_os_alloc_aligned(MI_REGION_SIZE, MI_SEGMENT_ALIGN, mi_option_is_enabled(mi_option_eager_region_commit), tld);
@ -154,9 +154,9 @@ static bool mi_region_commit_blocks(mem_region_t* region, size_t idx, size_t bit
// we assign it to a later slot instead (up to 4 tries).
// note: we don't need to increment the region count, this will happen on another allocation
for(size_t i = 1; i <= 4 && idx + i < MI_REGION_MAX; i++) {
void* s = mi_atomic_read_ptr_relaxed(&regions[idx+i].start);
void* s = mi_atomic_read_ptr(&regions[idx+i].start);
if (s == NULL) { // quick test
if (mi_atomic_cas_ptr_weak(&regions[idx+i].start, start, s)) {
if (mi_atomic_cas_ptr_strong(&regions[idx+i].start, start, NULL)) {
start = NULL;
break;
}
@ -167,10 +167,10 @@ static bool mi_region_commit_blocks(mem_region_t* region, size_t idx, size_t bit
_mi_os_free(start, MI_REGION_SIZE, tld->stats);
}
// and continue with the memory at our index
start = mi_atomic_read_ptr_relaxed(&region->start);
start = mi_atomic_read_ptr(&region->start);
}
}
mi_assert_internal(start == mi_atomic_read_ptr_relaxed(&region->start));
mi_assert_internal(start == mi_atomic_read_ptr(&region->start));
mi_assert_internal(start != NULL);
// Commit the blocks to memory
@ -230,7 +230,7 @@ static bool mi_region_alloc_blocks(mem_region_t* region, size_t idx, size_t bloc
const uintptr_t mask = mi_region_block_mask(blocks, 0);
const size_t bitidx_max = MI_REGION_MAP_BITS - blocks;
uintptr_t map = mi_atomic_read_relaxed(&region->map);
uintptr_t map = mi_atomic_read(&region->map);
#ifdef MI_HAVE_BITSCAN
size_t bitidx = mi_bsf(~map); // quickly find the first zero bit if possible
@ -245,9 +245,9 @@ static bool mi_region_alloc_blocks(mem_region_t* region, size_t idx, size_t bloc
mi_assert_internal((m >> bitidx) == mask); // no overflow?
uintptr_t newmap = map | m;
mi_assert_internal((newmap^map) >> bitidx == mask);
if (!mi_atomic_cas_strong(&region->map, newmap, map)) {
if (!mi_atomic_cas_weak(&region->map, newmap, map)) {
// no success, another thread claimed concurrently.. keep going
map = mi_atomic_read_relaxed(&region->map);
map = mi_atomic_read(&region->map);
continue;
}
else {
@ -317,7 +317,7 @@ void* _mi_mem_alloc_aligned(size_t size, size_t alignment, bool commit, size_t*
// find a range of free blocks
void* p = NULL;
size_t count = mi_atomic_read_relaxed(&regions_count);
size_t count = mi_atomic_read(&regions_count);
size_t idx = tld->region_idx; // start index is per-thread to reduce contention
for (size_t visited = 0; visited < count; visited++, idx++) {
if (idx >= count) idx = 0; // wrap around
@ -377,7 +377,7 @@ void _mi_mem_free(void* p, size_t size, size_t id, mi_stats_t* stats) {
mi_assert_internal(idx < MI_REGION_MAX); if (idx >= MI_REGION_MAX) return; // or `abort`?
mem_region_t* region = &regions[idx];
mi_assert_internal((mi_atomic_read_relaxed(&region->map) & mask) == mask ); // claimed?
void* start = mi_atomic_read_ptr_relaxed(&region->start);
void* start = mi_atomic_read_ptr(&region->start);
mi_assert_internal(start != NULL);
void* blocks_start = (uint8_t*)start + (bitidx * MI_SEGMENT_SIZE);
mi_assert_internal(blocks_start == p); // not a pointer in our area?

4
src/stats.c
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@ -38,8 +38,8 @@ static void mi_stat_update(mi_stat_count_t* stat, int64_t amount) {
if (mi_is_in_main(stat))
{
// add atomically (for abandoned pages)
int64_t current = mi_atomic_add64(&stat->current,amount);
if (current > stat->peak) stat->peak = stat->current; // racing.. it's ok
mi_atomic_add64(&stat->current,amount);
if (stat->current > stat->peak) stat->peak = stat->current; // racing.. it's ok
if (amount > 0) {
mi_atomic_add64(&stat->allocated,amount);
}