用线程缓存批量复用小对象

103tcache_alloc_small(tsd_t *tsd, arena_t *arena, tcache_t *tcache, size_t size,104    szind_t binind, bool zero, bool slow_path) {105	void *ret;106	bool  tcache_success;107108	assert(binind < SC_NBINS);109	cache_bin_t *bin = &tcache->bins[binind];110	ret = cache_bin_alloc(bin, &tcache_success);111	assert(tcache_success == (ret != NULL));112	if (unlikely(!tcache_success)) {113		bool tcache_hard_success;114		arena = arena_choose(tsd, arena);115		if (unlikely(arena == NULL)) {116			return NULL;117		}118		if (unlikely(tcache_bin_disabled(119		        binind, bin, tcache->tcache_slow))) {120			/* stats and zero are handled directly by the arena. */121			return arena_malloc_hard(tsd_tsdn(tsd), arena, size,122			    binind, zero, /* slab */ true);

391	/*392	 * This may read from the empty position; however the loaded value won't393	 * be used.  It's safe because the stack has one more slot reserved.394	 */395	void          *ret = *bin->stack_head;396	cache_bin_sz_t low_bits = (cache_bin_sz_t)(uintptr_t)bin->stack_head;397	void         **new_head = bin->stack_head + 1;398399	/*400	 * Note that the low water mark is at most empty; if we pass this check,401	 * we know we're non-empty.402	 */403	if (likely(low_bits != bin->low_bits_low_water)) {404		bin->stack_head = new_head;405		*success = true;406		return ret;407	}

430	cache_bin_sz_t ncached_max = cache_bin_ncached_max_get(cache_bin);431	cache_bin_sz_t nfill = tcache_slow->bin_nfill[binind];432	assert(nfill > 0 && nfill <= ncached_max);433	/* Let the arena finish draining a slab beyond the adaptive minimum. */434	cache_bin_sz_t nfill_min = nfill;435	cache_bin_sz_t nfill_max = tcache_ncached_target_max(ncached_max);436	CACHE_BIN_PTR_ARRAY_DECLARE(ptrs, nfill_max);437	cache_bin_init_ptr_array_for_fill(cache_bin, &ptrs, nfill_max);438439	cache_bin_sz_t filled = arena_ptr_array_fill_small(tsdn, arena, binind,440	    &ptrs, /* nfill_min */ nfill_min, /* nfill_max */ nfill_max,441	    cache_bin->tstats);442	cache_bin_finish_fill(cache_bin, &ptrs, filled);443	assert(filled >= nfill_min && filled <= nfill_max);444	assert(cache_bin_ncached_get_local(cache_bin) == filled);445446	tcache_slow->bin_nretain[binind] =447	    tcache_ncached_retain_after_refill(448	        tcache_slow->bin_nretain[binind], filled, ncached_max);449	tcache_slow->bin_nfill[binind] = tcache_ncached_fill_after_refill(450	    tcache_slow->bin_nfill[binind], ncached_max);451	ret = cache_bin_alloc(cache_bin, tcache_success);

481 * Free an object into the given bin.  Fails only if the bin is full.482 */483JEMALLOC_ALWAYS_INLINE bool484cache_bin_dalloc_easy(cache_bin_t *bin, void *ptr) {485	if (unlikely(cache_bin_full(bin))) {486		return false;487	}488489	if (unlikely(cache_bin_dalloc_safety_checks(bin, ptr))) {490		return true;491	}492493	bin->stack_head--;494	*bin->stack_head = ptr;495	cache_bin_assert_earlier(bin, bin->low_bits_full,496	    (cache_bin_sz_t)(uintptr_t)bin->stack_head);497498	return true;499}

209	if (unlikely(!cache_bin_dalloc_easy(bin, ptr))) {210		if (unlikely(tcache_bin_disabled(211		        binind, bin, tcache->tcache_slow))) {212			arena_dalloc_small(tsd_tsdn(tsd), ptr);213			return;214		}215		cache_bin_sz_t max = cache_bin_ncached_max_get(bin);216		cache_bin_sz_t *nretain =217		    &tcache->tcache_slow->bin_nretain[binind];218		*nretain = tcache_ncached_retain_after_overflow(*nretain, max);219		unsigned remain =220		    (unsigned)tcache_ncached_flush_remain(*nretain, max);221		tcache_bin_flush_small(tsd, tcache, bin, binind, remain);222		bool ret = cache_bin_dalloc_easy(bin, ptr);223		assert(ret);224	}