/* * rculfhash.c * * Userspace RCU library - Lock-Free Resizable RCU Hash Table * * Copyright 2010-2011 - Mathieu Desnoyers * Copyright 2011 - Lai Jiangshan * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /* * Based on the following articles: * - Ori Shalev and Nir Shavit. Split-ordered lists: Lock-free * extensible hash tables. J. ACM 53, 3 (May 2006), 379-405. * - Michael, M. M. High performance dynamic lock-free hash tables * and list-based sets. In Proceedings of the fourteenth annual ACM * symposium on Parallel algorithms and architectures, ACM Press, * (2002), 73-82. * * Some specificities of this Lock-Free Resizable RCU Hash Table * implementation: * * - RCU read-side critical section allows readers to perform hash * table lookups, as well as traversals, and use the returned objects * safely by allowing memory reclaim to take place only after a grace * period. * - Add and remove operations are lock-free, and do not need to * allocate memory. They need to be executed within RCU read-side * critical section to ensure the objects they read are valid and to * deal with the cmpxchg ABA problem. * - add and add_unique operations are supported. add_unique checks if * the node key already exists in the hash table. It ensures not to * populate a duplicate key if the node key already exists in the hash * table. * - The resize operation executes concurrently with * add/add_unique/add_replace/remove/lookup/traversal. * - Hash table nodes are contained within a split-ordered list. This * list is ordered by incrementing reversed-bits-hash value. * - An index of bucket nodes is kept. These bucket nodes are the hash * table "buckets". These buckets are internal nodes that allow to * perform a fast hash lookup, similarly to a skip list. These * buckets are chained together in the split-ordered list, which * allows recursive expansion by inserting new buckets between the * existing buckets. The split-ordered list allows adding new buckets * between existing buckets as the table needs to grow. * - The resize operation for small tables only allows expanding the * hash table. It is triggered automatically by detecting long chains * in the add operation. * - The resize operation for larger tables (and available through an * API) allows both expanding and shrinking the hash table. * - Split-counters are used to keep track of the number of * nodes within the hash table for automatic resize triggering. * - Resize operation initiated by long chain detection is executed by a * worker thread, which keeps lock-freedom of add and remove. * - Resize operations are protected by a mutex. * - The removal operation is split in two parts: first, a "removed" * flag is set in the next pointer within the node to remove. Then, * a "garbage collection" is performed in the bucket containing the * removed node (from the start of the bucket up to the removed node). * All encountered nodes with "removed" flag set in their next * pointers are removed from the linked-list. If the cmpxchg used for * removal fails (due to concurrent garbage-collection or concurrent * add), we retry from the beginning of the bucket. This ensures that * the node with "removed" flag set is removed from the hash table * (not visible to lookups anymore) before the RCU read-side critical * section held across removal ends. Furthermore, this ensures that * the node with "removed" flag set is removed from the linked-list * before its memory is reclaimed. After setting the "removal" flag, * only the thread which removal is the first to set the "removal * owner" flag (with an xchg) into a node's next pointer is considered * to have succeeded its removal (and thus owns the node to reclaim). * Because we garbage-collect starting from an invariant node (the * start-of-bucket bucket node) up to the "removed" node (or find a * reverse-hash that is higher), we are sure that a successful * traversal of the chain leads to a chain that is present in the * linked-list (the start node is never removed) and that it does not * contain the "removed" node anymore, even if concurrent delete/add * operations are changing the structure of the list concurrently. * - The add operations perform garbage collection of buckets if they * encounter nodes with removed flag set in the bucket where they want * to add their new node. This ensures lock-freedom of add operation by * helping the remover unlink nodes from the list rather than to wait * for it do to so. * - There are three memory backends for the hash table buckets: the * "order table", the "chunks", and the "mmap". * - These bucket containers contain a compact version of the hash table * nodes. * - The RCU "order table": * - has a first level table indexed by log2(hash index) which is * copied and expanded by the resize operation. This order table * allows finding the "bucket node" tables. * - There is one bucket node table per hash index order. The size of * each bucket node table is half the number of hashes contained in * this order (except for order 0). * - The RCU "chunks" is best suited for close interaction with a page * allocator. It uses a linear array as index to "chunks" containing * each the same number of buckets. * - The RCU "mmap" memory backend uses a single memory map to hold * all buckets. * - synchronize_rcu is used to garbage-collect the old bucket node table. * * Ordering Guarantees: * * To discuss these guarantees, we first define "read" operation as any * of the the basic cds_lfht_lookup, cds_lfht_next_duplicate, * cds_lfht_first, cds_lfht_next operation, as well as * cds_lfht_add_unique (failure). * * We define "read traversal" operation as any of the following * group of operations * - cds_lfht_lookup followed by iteration with cds_lfht_next_duplicate * (and/or cds_lfht_next, although less common). * - cds_lfht_add_unique (failure) followed by iteration with * cds_lfht_next_duplicate (and/or cds_lfht_next, although less * common). * - cds_lfht_first followed iteration with cds_lfht_next (and/or * cds_lfht_next_duplicate, although less common). * * We define "write" operations as any of cds_lfht_add, cds_lfht_replace, * cds_lfht_add_unique (success), cds_lfht_add_replace, cds_lfht_del. * * When cds_lfht_add_unique succeeds (returns the node passed as * parameter), it acts as a "write" operation. When cds_lfht_add_unique * fails (returns a node different from the one passed as parameter), it * acts as a "read" operation. A cds_lfht_add_unique failure is a * cds_lfht_lookup "read" operation, therefore, any ordering guarantee * referring to "lookup" imply any of "lookup" or cds_lfht_add_unique * (failure). * * We define "prior" and "later" node as nodes observable by reads and * read traversals respectively before and after a write or sequence of * write operations. * * Hash-table operations are often cascaded, for example, the pointer * returned by a cds_lfht_lookup() might be passed to a cds_lfht_next(), * whose return value might in turn be passed to another hash-table * operation. This entire cascaded series of operations must be enclosed * by a pair of matching rcu_read_lock() and rcu_read_unlock() * operations. * * The following ordering guarantees are offered by this hash table: * * A.1) "read" after "write": if there is ordering between a write and a * later read, then the read is guaranteed to see the write or some * later write. * A.2) "read traversal" after "write": given that there is dependency * ordering between reads in a "read traversal", if there is * ordering between a write and the first read of the traversal, * then the "read traversal" is guaranteed to see the write or * some later write. * B.1) "write" after "read": if there is ordering between a read and a * later write, then the read will never see the write. * B.2) "write" after "read traversal": given that there is dependency * ordering between reads in a "read traversal", if there is * ordering between the last read of the traversal and a later * write, then the "read traversal" will never see the write. * C) "write" while "read traversal": if a write occurs during a "read * traversal", the traversal may, or may not, see the write. * D.1) "write" after "write": if there is ordering between a write and * a later write, then the later write is guaranteed to see the * effects of the first write. * D.2) Concurrent "write" pairs: The system will assign an arbitrary * order to any pair of concurrent conflicting writes. * Non-conflicting writes (for example, to different keys) are * unordered. * E) If a grace period separates a "del" or "replace" operation * and a subsequent operation, then that subsequent operation is * guaranteed not to see the removed item. * F) Uniqueness guarantee: given a hash table that does not contain * duplicate items for a given key, there will only be one item in * the hash table after an arbitrary sequence of add_unique and/or * add_replace operations. Note, however, that a pair of * concurrent read operations might well access two different items * with that key. * G.1) If a pair of lookups for a given key are ordered (e.g. by a * memory barrier), then the second lookup will return the same * node as the previous lookup, or some later node. * G.2) A "read traversal" that starts after the end of a prior "read * traversal" (ordered by memory barriers) is guaranteed to see the * same nodes as the previous traversal, or some later nodes. * G.3) Concurrent "read" pairs: concurrent reads are unordered. For * example, if a pair of reads to the same key run concurrently * with an insertion of that same key, the reads remain unordered * regardless of their return values. In other words, you cannot * rely on the values returned by the reads to deduce ordering. * * Progress guarantees: * * * Reads are wait-free. These operations always move forward in the * hash table linked list, and this list has no loop. * * Writes are lock-free. Any retry loop performed by a write operation * is triggered by progress made within another update operation. * * Bucket node tables: * * hash table hash table the last all bucket node tables * order size bucket node 0 1 2 3 4 5 6(index) * table size * 0 1 1 1 * 1 2 1 1 1 * 2 4 2 1 1 2 * 3 8 4 1 1 2 4 * 4 16 8 1 1 2 4 8 * 5 32 16 1 1 2 4 8 16 * 6 64 32 1 1 2 4 8 16 32 * * When growing/shrinking, we only focus on the last bucket node table * which size is (!order ? 1 : (1 << (order -1))). * * Example for growing/shrinking: * grow hash table from order 5 to 6: init the index=6 bucket node table * shrink hash table from order 6 to 5: fini the index=6 bucket node table * * A bit of ascii art explanation: * * The order index is the off-by-one compared to the actual power of 2 * because we use index 0 to deal with the 0 special-case. * * This shows the nodes for a small table ordered by reversed bits: * * bits reverse * 0 000 000 * 4 100 001 * 2 010 010 * 6 110 011 * 1 001 100 * 5 101 101 * 3 011 110 * 7 111 111 * * This shows the nodes in order of non-reversed bits, linked by * reversed-bit order. * * order bits reverse * 0 0 000 000 * 1 | 1 001 100 <- * 2 | | 2 010 010 <- | * | | | 3 011 110 | <- | * 3 -> | | | 4 100 001 | | * -> | | 5 101 101 | * -> | 6 110 011 * -> 7 111 111 */ #define _LGPL_SOURCE #include #include #include #include #include #include #include #include #include "compat-getcpu.h" #include #include #include #include #include #include #include #include #include #include #include #include "workqueue.h" #include "urcu-die.h" /* * Split-counters lazily update the global counter each 1024 * addition/removal. It automatically keeps track of resize required. * We use the bucket length as indicator for need to expand for small * tables and machines lacking per-cpu data support. */ #define COUNT_COMMIT_ORDER 10 #define DEFAULT_SPLIT_COUNT_MASK 0xFUL #define CHAIN_LEN_TARGET 1 #define CHAIN_LEN_RESIZE_THRESHOLD 3 /* * Define the minimum table size. */ #define MIN_TABLE_ORDER 0 #define MIN_TABLE_SIZE (1UL << MIN_TABLE_ORDER) /* * Minimum number of bucket nodes to touch per thread to parallelize grow/shrink. */ #define MIN_PARTITION_PER_THREAD_ORDER 12 #define MIN_PARTITION_PER_THREAD (1UL << MIN_PARTITION_PER_THREAD_ORDER) /* * The removed flag needs to be updated atomically with the pointer. * It indicates that no node must attach to the node scheduled for * removal, and that node garbage collection must be performed. * The bucket flag does not require to be updated atomically with the * pointer, but it is added as a pointer low bit flag to save space. * The "removal owner" flag is used to detect which of the "del" * operation that has set the "removed flag" gets to return the removed * node to its caller. Note that the replace operation does not need to * iteract with the "removal owner" flag, because it validates that * the "removed" flag is not set before performing its cmpxchg. */ #define REMOVED_FLAG (1UL << 0) #define BUCKET_FLAG (1UL << 1) #define REMOVAL_OWNER_FLAG (1UL << 2) #define FLAGS_MASK ((1UL << 3) - 1) /* Value of the end pointer. Should not interact with flags. */ #define END_VALUE NULL /* * ht_items_count: Split-counters counting the number of node addition * and removal in the table. Only used if the CDS_LFHT_ACCOUNTING flag * is set at hash table creation. * * These are free-running counters, never reset to zero. They count the * number of add/remove, and trigger every (1 << COUNT_COMMIT_ORDER) * operations to update the global counter. We choose a power-of-2 value * for the trigger to deal with 32 or 64-bit overflow of the counter. */ struct ht_items_count { unsigned long add, del; } __attribute__((aligned(CAA_CACHE_LINE_SIZE))); /* * resize_work: Contains arguments passed to worker thread * responsible for performing lazy resize. */ struct resize_work { struct urcu_work work; struct cds_lfht *ht; }; /* * partition_resize_work: Contains arguments passed to worker threads * executing the hash table resize on partitions of the hash table * assigned to each processor's worker thread. */ struct partition_resize_work { pthread_t thread_id; struct cds_lfht *ht; unsigned long i, start, len; void (*fct)(struct cds_lfht *ht, unsigned long i, unsigned long start, unsigned long len); }; static struct urcu_workqueue *cds_lfht_workqueue; static unsigned long cds_lfht_workqueue_user_count; /* * Mutex ensuring mutual exclusion between workqueue initialization and * fork handlers. cds_lfht_fork_mutex nests inside call_rcu_mutex. */ static pthread_mutex_t cds_lfht_fork_mutex = PTHREAD_MUTEX_INITIALIZER; static struct urcu_atfork cds_lfht_atfork; /* * atfork handler nesting counters. Handle being registered to many urcu * flavors, thus being possibly invoked more than once in the * pthread_atfork list of callbacks. */ static int cds_lfht_workqueue_atfork_nesting; static void cds_lfht_init_worker(const struct rcu_flavor_struct *flavor); static void cds_lfht_fini_worker(const struct rcu_flavor_struct *flavor); /* * Algorithm to reverse bits in a word by lookup table, extended to * 64-bit words. * Source: * http://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable * Originally from Public Domain. */ static const uint8_t BitReverseTable256[256] = { #define R2(n) (n), (n) + 2*64, (n) + 1*64, (n) + 3*64 #define R4(n) R2(n), R2((n) + 2*16), R2((n) + 1*16), R2((n) + 3*16) #define R6(n) R4(n), R4((n) + 2*4 ), R4((n) + 1*4 ), R4((n) + 3*4 ) R6(0), R6(2), R6(1), R6(3) }; #undef R2 #undef R4 #undef R6 static uint8_t bit_reverse_u8(uint8_t v) { return BitReverseTable256[v]; } #if (CAA_BITS_PER_LONG == 32) static uint32_t bit_reverse_u32(uint32_t v) { return ((uint32_t) bit_reverse_u8(v) << 24) | ((uint32_t) bit_reverse_u8(v >> 8) << 16) | ((uint32_t) bit_reverse_u8(v >> 16) << 8) | ((uint32_t) bit_reverse_u8(v >> 24)); } #else static uint64_t bit_reverse_u64(uint64_t v) { return ((uint64_t) bit_reverse_u8(v) << 56) | ((uint64_t) bit_reverse_u8(v >> 8) << 48) | ((uint64_t) bit_reverse_u8(v >> 16) << 40) | ((uint64_t) bit_reverse_u8(v >> 24) << 32) | ((uint64_t) bit_reverse_u8(v >> 32) << 24) | ((uint64_t) bit_reverse_u8(v >> 40) << 16) | ((uint64_t) bit_reverse_u8(v >> 48) << 8) | ((uint64_t) bit_reverse_u8(v >> 56)); } #endif static unsigned long bit_reverse_ulong(unsigned long v) { #if (CAA_BITS_PER_LONG == 32) return bit_reverse_u32(v); #else return bit_reverse_u64(v); #endif } /* * fls: returns the position of the most significant bit. * Returns 0 if no bit is set, else returns the position of the most * significant bit (from 1 to 32 on 32-bit, from 1 to 64 on 64-bit). */ #if defined(__i386) || defined(__x86_64) static inline unsigned int fls_u32(uint32_t x) { int r; __asm__ ("bsrl %1,%0\n\t" "jnz 1f\n\t" "movl $-1,%0\n\t" "1:\n\t" : "=r" (r) : "rm" (x)); return r + 1; } #define HAS_FLS_U32 #endif #if defined(__x86_64) static inline unsigned int fls_u64(uint64_t x) { long r; __asm__ ("bsrq %1,%0\n\t" "jnz 1f\n\t" "movq $-1,%0\n\t" "1:\n\t" : "=r" (r) : "rm" (x)); return r + 1; } #define HAS_FLS_U64 #endif #ifndef HAS_FLS_U64 static __attribute__((unused)) unsigned int fls_u64(uint64_t x) { unsigned int r = 64; if (!x) return 0; if (!(x & 0xFFFFFFFF00000000ULL)) { x <<= 32; r -= 32; } if (!(x & 0xFFFF000000000000ULL)) { x <<= 16; r -= 16; } if (!(x & 0xFF00000000000000ULL)) { x <<= 8; r -= 8; } if (!(x & 0xF000000000000000ULL)) { x <<= 4; r -= 4; } if (!(x & 0xC000000000000000ULL)) { x <<= 2; r -= 2; } if (!(x & 0x8000000000000000ULL)) { x <<= 1; r -= 1; } return r; } #endif #ifndef HAS_FLS_U32 static __attribute__((unused)) unsigned int fls_u32(uint32_t x) { unsigned int r = 32; if (!x) return 0; if (!(x & 0xFFFF0000U)) { x <<= 16; r -= 16; } if (!(x & 0xFF000000U)) { x <<= 8; r -= 8; } if (!(x & 0xF0000000U)) { x <<= 4; r -= 4; } if (!(x & 0xC0000000U)) { x <<= 2; r -= 2; } if (!(x & 0x80000000U)) { x <<= 1; r -= 1; } return r; } #endif unsigned int cds_lfht_fls_ulong(unsigned long x) { #if (CAA_BITS_PER_LONG == 32) return fls_u32(x); #else return fls_u64(x); #endif } /* * Return the minimum order for which x <= (1UL << order). * Return -1 if x is 0. */ int cds_lfht_get_count_order_u32(uint32_t x) { if (!x) return -1; return fls_u32(x - 1); } /* * Return the minimum order for which x <= (1UL << order). * Return -1 if x is 0. */ int cds_lfht_get_count_order_ulong(unsigned long x) { if (!x) return -1; return cds_lfht_fls_ulong(x - 1); } static void cds_lfht_resize_lazy_grow(struct cds_lfht *ht, unsigned long size, int growth); static void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size, unsigned long count); static void mutex_lock(pthread_mutex_t *mutex) { int ret; #ifndef DISTRUST_SIGNALS_EXTREME ret = pthread_mutex_lock(mutex); if (ret) urcu_die(ret); #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ while ((ret = pthread_mutex_trylock(mutex)) != 0) { if (ret != EBUSY && ret != EINTR) urcu_die(ret); if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) { cmm_smp_mb(); _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); cmm_smp_mb(); } (void) poll(NULL, 0, 10); } #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } static void mutex_unlock(pthread_mutex_t *mutex) { int ret; ret = pthread_mutex_unlock(mutex); if (ret) urcu_die(ret); } static long nr_cpus_mask = -1; static long split_count_mask = -1; static int split_count_order = -1; #if defined(HAVE_SYSCONF) static void ht_init_nr_cpus_mask(void) { long maxcpus; maxcpus = sysconf(_SC_NPROCESSORS_CONF); if (maxcpus <= 0) { nr_cpus_mask = -2; return; } /* * round up number of CPUs to next power of two, so we * can use & for modulo. */ maxcpus = 1UL << cds_lfht_get_count_order_ulong(maxcpus); nr_cpus_mask = maxcpus - 1; } #else /* #if defined(HAVE_SYSCONF) */ static void ht_init_nr_cpus_mask(void) { nr_cpus_mask = -2; } #endif /* #else #if defined(HAVE_SYSCONF) */ static void alloc_split_items_count(struct cds_lfht *ht) { if (nr_cpus_mask == -1) { ht_init_nr_cpus_mask(); if (nr_cpus_mask < 0) split_count_mask = DEFAULT_SPLIT_COUNT_MASK; else split_count_mask = nr_cpus_mask; split_count_order = cds_lfht_get_count_order_ulong(split_count_mask + 1); } assert(split_count_mask >= 0); if (ht->flags & CDS_LFHT_ACCOUNTING) { ht->split_count = calloc(split_count_mask + 1, sizeof(struct ht_items_count)); assert(ht->split_count); } else { ht->split_count = NULL; } } static void free_split_items_count(struct cds_lfht *ht) { poison_free(ht->split_count); } static int ht_get_split_count_index(unsigned long hash) { int cpu; assert(split_count_mask >= 0); cpu = urcu_sched_getcpu(); if (caa_unlikely(cpu < 0)) return hash & split_count_mask; else return cpu & split_count_mask; } static void ht_count_add(struct cds_lfht *ht, unsigned long size, unsigned long hash) { unsigned long split_count; int index; long count; if (caa_unlikely(!ht->split_count)) return; index = ht_get_split_count_index(hash); split_count = uatomic_add_return(&ht->split_count[index].add, 1); if (caa_likely(split_count & ((1UL << COUNT_COMMIT_ORDER) - 1))) return; /* Only if number of add multiple of 1UL << COUNT_COMMIT_ORDER */ dbg_printf("add split count %lu\n", split_count); count = uatomic_add_return(&ht->count, 1UL << COUNT_COMMIT_ORDER); if (caa_likely(count & (count - 1))) return; /* Only if global count is power of 2 */ if ((count >> CHAIN_LEN_RESIZE_THRESHOLD) < size) return; dbg_printf("add set global %ld\n", count); cds_lfht_resize_lazy_count(ht, size, count >> (CHAIN_LEN_TARGET - 1)); } static void ht_count_del(struct cds_lfht *ht, unsigned long size, unsigned long hash) { unsigned long split_count; int index; long count; if (caa_unlikely(!ht->split_count)) return; index = ht_get_split_count_index(hash); split_count = uatomic_add_return(&ht->split_count[index].del, 1); if (caa_likely(split_count & ((1UL << COUNT_COMMIT_ORDER) - 1))) return; /* Only if number of deletes multiple of 1UL << COUNT_COMMIT_ORDER */ dbg_printf("del split count %lu\n", split_count); count = uatomic_add_return(&ht->count, -(1UL << COUNT_COMMIT_ORDER)); if (caa_likely(count & (count - 1))) return; /* Only if global count is power of 2 */ if ((count >> CHAIN_LEN_RESIZE_THRESHOLD) >= size) return; dbg_printf("del set global %ld\n", count); /* * Don't shrink table if the number of nodes is below a * certain threshold. */ if (count < (1UL << COUNT_COMMIT_ORDER) * (split_count_mask + 1)) return; cds_lfht_resize_lazy_count(ht, size, count >> (CHAIN_LEN_TARGET - 1)); } static void check_resize(struct cds_lfht *ht, unsigned long size, uint32_t chain_len) { unsigned long count; if (!(ht->flags & CDS_LFHT_AUTO_RESIZE)) return; count = uatomic_read(&ht->count); /* * Use bucket-local length for small table expand and for * environments lacking per-cpu data support. */ if (count >= (1UL << (COUNT_COMMIT_ORDER + split_count_order))) return; if (chain_len > 100) dbg_printf("WARNING: large chain length: %u.\n", chain_len); if (chain_len >= CHAIN_LEN_RESIZE_THRESHOLD) { int growth; /* * Ideal growth calculated based on chain length. */ growth = cds_lfht_get_count_order_u32(chain_len - (CHAIN_LEN_TARGET - 1)); if ((ht->flags & CDS_LFHT_ACCOUNTING) && (size << growth) >= (1UL << (COUNT_COMMIT_ORDER + split_count_order))) { /* * If ideal growth expands the hash table size * beyond the "small hash table" sizes, use the * maximum small hash table size to attempt * expanding the hash table. This only applies * when node accounting is available, otherwise * the chain length is used to expand the hash * table in every case. */ growth = COUNT_COMMIT_ORDER + split_count_order - cds_lfht_get_count_order_ulong(size); if (growth <= 0) return; } cds_lfht_resize_lazy_grow(ht, size, growth); } } static struct cds_lfht_node *clear_flag(struct cds_lfht_node *node) { return (struct cds_lfht_node *) (((unsigned long) node) & ~FLAGS_MASK); } static int is_removed(struct cds_lfht_node *node) { return ((unsigned long) node) & REMOVED_FLAG; } static int is_bucket(struct cds_lfht_node *node) { return ((unsigned long) node) & BUCKET_FLAG; } static struct cds_lfht_node *flag_bucket(struct cds_lfht_node *node) { return (struct cds_lfht_node *) (((unsigned long) node) | BUCKET_FLAG); } static int is_removal_owner(struct cds_lfht_node *node) { return ((unsigned long) node) & REMOVAL_OWNER_FLAG; } static struct cds_lfht_node *flag_removal_owner(struct cds_lfht_node *node) { return (struct cds_lfht_node *) (((unsigned long) node) | REMOVAL_OWNER_FLAG); } static struct cds_lfht_node *flag_removed_or_removal_owner(struct cds_lfht_node *node) { return (struct cds_lfht_node *) (((unsigned long) node) | REMOVED_FLAG | REMOVAL_OWNER_FLAG); } static struct cds_lfht_node *get_end(void) { return (struct cds_lfht_node *) END_VALUE; } static int is_end(struct cds_lfht_node *node) { return clear_flag(node) == (struct cds_lfht_node *) END_VALUE; } static unsigned long _uatomic_xchg_monotonic_increase(unsigned long *ptr, unsigned long v) { unsigned long old1, old2; old1 = uatomic_read(ptr); do { old2 = old1; if (old2 >= v) return old2; } while ((old1 = uatomic_cmpxchg(ptr, old2, v)) != old2); return old2; } static void cds_lfht_alloc_bucket_table(struct cds_lfht *ht, unsigned long order) { return ht->mm->alloc_bucket_table(ht, order); } /* * cds_lfht_free_bucket_table() should be called with decreasing order. * When cds_lfht_free_bucket_table(0) is called, it means the whole * lfht is destroyed. */ static void cds_lfht_free_bucket_table(struct cds_lfht *ht, unsigned long order) { return ht->mm->free_bucket_table(ht, order); } static inline struct cds_lfht_node *bucket_at(struct cds_lfht *ht, unsigned long index) { return ht->bucket_at(ht, index); } static inline struct cds_lfht_node *lookup_bucket(struct cds_lfht *ht, unsigned long size, unsigned long hash) { assert(size > 0); return bucket_at(ht, hash & (size - 1)); } /* * Remove all logically deleted nodes from a bucket up to a certain node key. */ static void _cds_lfht_gc_bucket(struct cds_lfht_node *bucket, struct cds_lfht_node *node) { struct cds_lfht_node *iter_prev, *iter, *next, *new_next; assert(!is_bucket(bucket)); assert(!is_removed(bucket)); assert(!is_removal_owner(bucket)); assert(!is_bucket(node)); assert(!is_removed(node)); assert(!is_removal_owner(node)); for (;;) { iter_prev = bucket; /* We can always skip the bucket node initially */ iter = rcu_dereference(iter_prev->next); assert(!is_removed(iter)); assert(!is_removal_owner(iter)); assert(iter_prev->reverse_hash <= node->reverse_hash); /* * We should never be called with bucket (start of chain) * and logically removed node (end of path compression * marker) being the actual same node. This would be a * bug in the algorithm implementation. */ assert(bucket != node); for (;;) { if (caa_unlikely(is_end(iter))) return; if (caa_likely(clear_flag(iter)->reverse_hash > node->reverse_hash)) return; next = rcu_dereference(clear_flag(iter)->next); if (caa_likely(is_removed(next))) break; iter_prev = clear_flag(iter); iter = next; } assert(!is_removed(iter)); assert(!is_removal_owner(iter)); if (is_bucket(iter)) new_next = flag_bucket(clear_flag(next)); else new_next = clear_flag(next); (void) uatomic_cmpxchg(&iter_prev->next, iter, new_next); } } static int _cds_lfht_replace(struct cds_lfht *ht, unsigned long size, struct cds_lfht_node *old_node, struct cds_lfht_node *old_next, struct cds_lfht_node *new_node) { struct cds_lfht_node *bucket, *ret_next; if (!old_node) /* Return -ENOENT if asked to replace NULL node */ return -ENOENT; assert(!is_removed(old_node)); assert(!is_removal_owner(old_node)); assert(!is_bucket(old_node)); assert(!is_removed(new_node)); assert(!is_removal_owner(new_node)); assert(!is_bucket(new_node)); assert(new_node != old_node); for (;;) { /* Insert after node to be replaced */ if (is_removed(old_next)) { /* * Too late, the old node has been removed under us * between lookup and replace. Fail. */ return -ENOENT; } assert(old_next == clear_flag(old_next)); assert(new_node != old_next); /* * REMOVAL_OWNER flag is _NEVER_ set before the REMOVED * flag. It is either set atomically at the same time * (replace) or after (del). */ assert(!is_removal_owner(old_next)); new_node->next = old_next; /* * Here is the whole trick for lock-free replace: we add * the replacement node _after_ the node we want to * replace by atomically setting its next pointer at the * same time we set its removal flag. Given that * the lookups/get next use an iterator aware of the * next pointer, they will either skip the old node due * to the removal flag and see the new node, or use * the old node, but will not see the new one. * This is a replacement of a node with another node * that has the same value: we are therefore not * removing a value from the hash table. We set both the * REMOVED and REMOVAL_OWNER flags atomically so we own * the node after successful cmpxchg. */ ret_next = uatomic_cmpxchg(&old_node->next, old_next, flag_removed_or_removal_owner(new_node)); if (ret_next == old_next) break; /* We performed the replacement. */ old_next = ret_next; } /* * Ensure that the old node is not visible to readers anymore: * lookup for the node, and remove it (along with any other * logically removed node) if found. */ bucket = lookup_bucket(ht, size, bit_reverse_ulong(old_node->reverse_hash)); _cds_lfht_gc_bucket(bucket, new_node); assert(is_removed(CMM_LOAD_SHARED(old_node->next))); return 0; } /* * A non-NULL unique_ret pointer uses the "add unique" (or uniquify) add * mode. A NULL unique_ret allows creation of duplicate keys. */ static void _cds_lfht_add(struct cds_lfht *ht, unsigned long hash, cds_lfht_match_fct match, const void *key, unsigned long size, struct cds_lfht_node *node, struct cds_lfht_iter *unique_ret, int bucket_flag) { struct cds_lfht_node *iter_prev, *iter, *next, *new_node, *new_next, *return_node; struct cds_lfht_node *bucket; assert(!is_bucket(node)); assert(!is_removed(node)); assert(!is_removal_owner(node)); bucket = lookup_bucket(ht, size, hash); for (;;) { uint32_t chain_len = 0; /* * iter_prev points to the non-removed node prior to the * insert location. */ iter_prev = bucket; /* We can always skip the bucket node initially */ iter = rcu_dereference(iter_prev->next); assert(iter_prev->reverse_hash <= node->reverse_hash); for (;;) { if (caa_unlikely(is_end(iter))) goto insert; if (caa_likely(clear_flag(iter)->reverse_hash > node->reverse_hash)) goto insert; /* bucket node is the first node of the identical-hash-value chain */ if (bucket_flag && clear_flag(iter)->reverse_hash == node->reverse_hash) goto insert; next = rcu_dereference(clear_flag(iter)->next); if (caa_unlikely(is_removed(next))) goto gc_node; /* uniquely add */ if (unique_ret && !is_bucket(next) && clear_flag(iter)->reverse_hash == node->reverse_hash) { struct cds_lfht_iter d_iter = { .node = node, .next = iter, }; /* * uniquely adding inserts the node as the first * node of the identical-hash-value node chain. * * This semantic ensures no duplicated keys * should ever be observable in the table * (including traversing the table node by * node by forward iterations) */ cds_lfht_next_duplicate(ht, match, key, &d_iter); if (!d_iter.node) goto insert; *unique_ret = d_iter; return; } /* Only account for identical reverse hash once */ if (iter_prev->reverse_hash != clear_flag(iter)->reverse_hash && !is_bucket(next)) check_resize(ht, size, ++chain_len); iter_prev = clear_flag(iter); iter = next; } insert: assert(node != clear_flag(iter)); assert(!is_removed(iter_prev)); assert(!is_removal_owner(iter_prev)); assert(!is_removed(iter)); assert(!is_removal_owner(iter)); assert(iter_prev != node); if (!bucket_flag) node->next = clear_flag(iter); else node->next = flag_bucket(clear_flag(iter)); if (is_bucket(iter)) new_node = flag_bucket(node); else new_node = node; if (uatomic_cmpxchg(&iter_prev->next, iter, new_node) != iter) { continue; /* retry */ } else { return_node = node; goto end; } gc_node: assert(!is_removed(iter)); assert(!is_removal_owner(iter)); if (is_bucket(iter)) new_next = flag_bucket(clear_flag(next)); else new_next = clear_flag(next); (void) uatomic_cmpxchg(&iter_prev->next, iter, new_next); /* retry */ } end: if (unique_ret) { unique_ret->node = return_node; /* unique_ret->next left unset, never used. */ } } static int _cds_lfht_del(struct cds_lfht *ht, unsigned long size, struct cds_lfht_node *node) { struct cds_lfht_node *bucket, *next; if (!node) /* Return -ENOENT if asked to delete NULL node */ return -ENOENT; /* logically delete the node */ assert(!is_bucket(node)); assert(!is_removed(node)); assert(!is_removal_owner(node)); /* * We are first checking if the node had previously been * logically removed (this check is not atomic with setting the * logical removal flag). Return -ENOENT if the node had * previously been removed. */ next = CMM_LOAD_SHARED(node->next); /* next is not dereferenced */ if (caa_unlikely(is_removed(next))) return -ENOENT; assert(!is_bucket(next)); /* * The del operation semantic guarantees a full memory barrier * before the uatomic_or atomic commit of the deletion flag. */ cmm_smp_mb__before_uatomic_or(); /* * We set the REMOVED_FLAG unconditionally. Note that there may * be more than one concurrent thread setting this flag. * Knowing which wins the race will be known after the garbage * collection phase, stay tuned! */ uatomic_or(&node->next, REMOVED_FLAG); /* We performed the (logical) deletion. */ /* * Ensure that the node is not visible to readers anymore: lookup for * the node, and remove it (along with any other logically removed node) * if found. */ bucket = lookup_bucket(ht, size, bit_reverse_ulong(node->reverse_hash)); _cds_lfht_gc_bucket(bucket, node); assert(is_removed(CMM_LOAD_SHARED(node->next))); /* * Last phase: atomically exchange node->next with a version * having "REMOVAL_OWNER_FLAG" set. If the returned node->next * pointer did _not_ have "REMOVAL_OWNER_FLAG" set, we now own * the node and win the removal race. * It is interesting to note that all "add" paths are forbidden * to change the next pointer starting from the point where the * REMOVED_FLAG is set, so here using a read, followed by a * xchg() suffice to guarantee that the xchg() will ever only * set the "REMOVAL_OWNER_FLAG" (or change nothing if the flag * was already set). */ if (!is_removal_owner(uatomic_xchg(&node->next, flag_removal_owner(node->next)))) return 0; else return -ENOENT; } static void *partition_resize_thread(void *arg) { struct partition_resize_work *work = arg; work->ht->flavor->register_thread(); work->fct(work->ht, work->i, work->start, work->len); work->ht->flavor->unregister_thread(); return NULL; } static void partition_resize_helper(struct cds_lfht *ht, unsigned long i, unsigned long len, void (*fct)(struct cds_lfht *ht, unsigned long i, unsigned long start, unsigned long len)) { unsigned long partition_len, start = 0; struct partition_resize_work *work; int thread, ret; unsigned long nr_threads; assert(nr_cpus_mask != -1); if (nr_cpus_mask < 0 || len < 2 * MIN_PARTITION_PER_THREAD) goto fallback; /* * Note: nr_cpus_mask + 1 is always power of 2. * We spawn just the number of threads we need to satisfy the minimum * partition size, up to the number of CPUs in the system. */ if (nr_cpus_mask > 0) { nr_threads = min(nr_cpus_mask + 1, len >> MIN_PARTITION_PER_THREAD_ORDER); } else { nr_threads = 1; } partition_len = len >> cds_lfht_get_count_order_ulong(nr_threads); work = calloc(nr_threads, sizeof(*work)); if (!work) { dbg_printf("error allocating for resize, single-threading\n"); goto fallback; } for (thread = 0; thread < nr_threads; thread++) { work[thread].ht = ht; work[thread].i = i; work[thread].len = partition_len; work[thread].start = thread * partition_len; work[thread].fct = fct; ret = pthread_create(&(work[thread].thread_id), ht->resize_attr, partition_resize_thread, &work[thread]); if (ret == EAGAIN) { /* * Out of resources: wait and join the threads * we've created, then handle leftovers. */ dbg_printf("error spawning for resize, single-threading\n"); start = work[thread].start; len -= start; nr_threads = thread; break; } assert(!ret); } for (thread = 0; thread < nr_threads; thread++) { ret = pthread_join(work[thread].thread_id, NULL); assert(!ret); } free(work); /* * A pthread_create failure above will either lead in us having * no threads to join or starting at a non-zero offset, * fallback to single thread processing of leftovers. */ if (start == 0 && nr_threads > 0) return; fallback: fct(ht, i, start, len); } /* * Holding RCU read lock to protect _cds_lfht_add against memory * reclaim that could be performed by other worker threads (ABA * problem). * * When we reach a certain length, we can split this population phase over * many worker threads, based on the number of CPUs available in the system. * This should therefore take care of not having the expand lagging behind too * many concurrent insertion threads by using the scheduler's ability to * schedule bucket node population fairly with insertions. */ static void init_table_populate_partition(struct cds_lfht *ht, unsigned long i, unsigned long start, unsigned long len) { unsigned long j, size = 1UL << (i - 1); assert(i > MIN_TABLE_ORDER); ht->flavor->read_lock(); for (j = size + start; j < size + start + len; j++) { struct cds_lfht_node *new_node = bucket_at(ht, j); assert(j >= size && j < (size << 1)); dbg_printf("init populate: order %lu index %lu hash %lu\n", i, j, j); new_node->reverse_hash = bit_reverse_ulong(j); _cds_lfht_add(ht, j, NULL, NULL, size, new_node, NULL, 1); } ht->flavor->read_unlock(); } static void init_table_populate(struct cds_lfht *ht, unsigned long i, unsigned long len) { partition_resize_helper(ht, i, len, init_table_populate_partition); } static void init_table(struct cds_lfht *ht, unsigned long first_order, unsigned long last_order) { unsigned long i; dbg_printf("init table: first_order %lu last_order %lu\n", first_order, last_order); assert(first_order > MIN_TABLE_ORDER); for (i = first_order; i <= last_order; i++) { unsigned long len; len = 1UL << (i - 1); dbg_printf("init order %lu len: %lu\n", i, len); /* Stop expand if the resize target changes under us */ if (CMM_LOAD_SHARED(ht->resize_target) < (1UL << i)) break; cds_lfht_alloc_bucket_table(ht, i); /* * Set all bucket nodes reverse hash values for a level and * link all bucket nodes into the table. */ init_table_populate(ht, i, len); /* * Update table size. */ cmm_smp_wmb(); /* populate data before RCU size */ CMM_STORE_SHARED(ht->size, 1UL << i); dbg_printf("init new size: %lu\n", 1UL << i); if (CMM_LOAD_SHARED(ht->in_progress_destroy)) break; } } /* * Holding RCU read lock to protect _cds_lfht_remove against memory * reclaim that could be performed by other worker threads (ABA * problem). * For a single level, we logically remove and garbage collect each node. * * As a design choice, we perform logical removal and garbage collection on a * node-per-node basis to simplify this algorithm. We also assume keeping good * cache locality of the operation would overweight possible performance gain * that could be achieved by batching garbage collection for multiple levels. * However, this would have to be justified by benchmarks. * * Concurrent removal and add operations are helping us perform garbage * collection of logically removed nodes. We guarantee that all logically * removed nodes have been garbage-collected (unlinked) before work * enqueue is invoked to free a hole level of bucket nodes (after a * grace period). * * Logical removal and garbage collection can therefore be done in batch * or on a node-per-node basis, as long as the guarantee above holds. * * When we reach a certain length, we can split this removal over many worker * threads, based on the number of CPUs available in the system. This should * take care of not letting resize process lag behind too many concurrent * updater threads actively inserting into the hash table. */ static void remove_table_partition(struct cds_lfht *ht, unsigned long i, unsigned long start, unsigned long len) { unsigned long j, size = 1UL << (i - 1); assert(i > MIN_TABLE_ORDER); ht->flavor->read_lock(); for (j = size + start; j < size + start + len; j++) { struct cds_lfht_node *fini_bucket = bucket_at(ht, j); struct cds_lfht_node *parent_bucket = bucket_at(ht, j - size); assert(j >= size && j < (size << 1)); dbg_printf("remove entry: order %lu index %lu hash %lu\n", i, j, j); /* Set the REMOVED_FLAG to freeze the ->next for gc */ uatomic_or(&fini_bucket->next, REMOVED_FLAG); _cds_lfht_gc_bucket(parent_bucket, fini_bucket); } ht->flavor->read_unlock(); } static void remove_table(struct cds_lfht *ht, unsigned long i, unsigned long len) { partition_resize_helper(ht, i, len, remove_table_partition); } /* * fini_table() is never called for first_order == 0, which is why * free_by_rcu_order == 0 can be used as criterion to know if free must * be called. */ static void fini_table(struct cds_lfht *ht, unsigned long first_order, unsigned long last_order) { long i; unsigned long free_by_rcu_order = 0; dbg_printf("fini table: first_order %lu last_order %lu\n", first_order, last_order); assert(first_order > MIN_TABLE_ORDER); for (i = last_order; i >= first_order; i--) { unsigned long len; len = 1UL << (i - 1); dbg_printf("fini order %ld len: %lu\n", i, len); /* Stop shrink if the resize target changes under us */ if (CMM_LOAD_SHARED(ht->resize_target) > (1UL << (i - 1))) break; cmm_smp_wmb(); /* populate data before RCU size */ CMM_STORE_SHARED(ht->size, 1UL << (i - 1)); /* * We need to wait for all add operations to reach Q.S. (and * thus use the new table for lookups) before we can start * releasing the old bucket nodes. Otherwise their lookup will * return a logically removed node as insert position. */ ht->flavor->update_synchronize_rcu(); if (free_by_rcu_order) cds_lfht_free_bucket_table(ht, free_by_rcu_order); /* * Set "removed" flag in bucket nodes about to be removed. * Unlink all now-logically-removed bucket node pointers. * Concurrent add/remove operation are helping us doing * the gc. */ remove_table(ht, i, len); free_by_rcu_order = i; dbg_printf("fini new size: %lu\n", 1UL << i); if (CMM_LOAD_SHARED(ht->in_progress_destroy)) break; } if (free_by_rcu_order) { ht->flavor->update_synchronize_rcu(); cds_lfht_free_bucket_table(ht, free_by_rcu_order); } } static void cds_lfht_create_bucket(struct cds_lfht *ht, unsigned long size) { struct cds_lfht_node *prev, *node; unsigned long order, len, i; cds_lfht_alloc_bucket_table(ht, 0); dbg_printf("create bucket: order 0 index 0 hash 0\n"); node = bucket_at(ht, 0); node->next = flag_bucket(get_end()); node->reverse_hash = 0; for (order = 1; order < cds_lfht_get_count_order_ulong(size) + 1; order++) { len = 1UL << (order - 1); cds_lfht_alloc_bucket_table(ht, order); for (i = 0; i < len; i++) { /* * Now, we are trying to init the node with the * hash=(len+i) (which is also a bucket with the * index=(len+i)) and insert it into the hash table, * so this node has to be inserted after the bucket * with the index=(len+i)&(len-1)=i. And because there * is no other non-bucket node nor bucket node with * larger index/hash inserted, so the bucket node * being inserted should be inserted directly linked * after the bucket node with index=i. */ prev = bucket_at(ht, i); node = bucket_at(ht, len + i); dbg_printf("create bucket: order %lu index %lu hash %lu\n", order, len + i, len + i); node->reverse_hash = bit_reverse_ulong(len + i); /* insert after prev */ assert(is_bucket(prev->next)); node->next = prev->next; prev->next = flag_bucket(node); } } } struct cds_lfht *_cds_lfht_new(unsigned long init_size, unsigned long min_nr_alloc_buckets, unsigned long max_nr_buckets, int flags, const struct cds_lfht_mm_type *mm, const struct rcu_flavor_struct *flavor, pthread_attr_t *attr) { struct cds_lfht *ht; unsigned long order; /* min_nr_alloc_buckets must be power of two */ if (!min_nr_alloc_buckets || (min_nr_alloc_buckets & (min_nr_alloc_buckets - 1))) return NULL; /* init_size must be power of two */ if (!init_size || (init_size & (init_size - 1))) return NULL; /* * Memory management plugin default. */ if (!mm) { if (CAA_BITS_PER_LONG > 32 && max_nr_buckets && max_nr_buckets <= (1ULL << 32)) { /* * For 64-bit architectures, with max number of * buckets small enough not to use the entire * 64-bit memory mapping space (and allowing a * fair number of hash table instances), use the * mmap allocator, which is faster than the * order allocator. */ mm = &cds_lfht_mm_mmap; } else { /* * The fallback is to use the order allocator. */ mm = &cds_lfht_mm_order; } } /* max_nr_buckets == 0 for order based mm means infinite */ if (mm == &cds_lfht_mm_order && !max_nr_buckets) max_nr_buckets = 1UL << (MAX_TABLE_ORDER - 1); /* max_nr_buckets must be power of two */ if (!max_nr_buckets || (max_nr_buckets & (max_nr_buckets - 1))) return NULL; if (flags & CDS_LFHT_AUTO_RESIZE) cds_lfht_init_worker(flavor); min_nr_alloc_buckets = max(min_nr_alloc_buckets, MIN_TABLE_SIZE); init_size = max(init_size, MIN_TABLE_SIZE); max_nr_buckets = max(max_nr_buckets, min_nr_alloc_buckets); init_size = min(init_size, max_nr_buckets); ht = mm->alloc_cds_lfht(min_nr_alloc_buckets, max_nr_buckets); assert(ht); assert(ht->mm == mm); assert(ht->bucket_at == mm->bucket_at); ht->flags = flags; ht->flavor = flavor; ht->resize_attr = attr; alloc_split_items_count(ht); /* this mutex should not nest in read-side C.S. */ pthread_mutex_init(&ht->resize_mutex, NULL); order = cds_lfht_get_count_order_ulong(init_size); ht->resize_target = 1UL << order; cds_lfht_create_bucket(ht, 1UL << order); ht->size = 1UL << order; return ht; } void cds_lfht_lookup(struct cds_lfht *ht, unsigned long hash, cds_lfht_match_fct match, const void *key, struct cds_lfht_iter *iter) { struct cds_lfht_node *node, *next, *bucket; unsigned long reverse_hash, size; reverse_hash = bit_reverse_ulong(hash); size = rcu_dereference(ht->size); bucket = lookup_bucket(ht, size, hash); /* We can always skip the bucket node initially */ node = rcu_dereference(bucket->next); node = clear_flag(node); for (;;) { if (caa_unlikely(is_end(node))) { node = next = NULL; break; } if (caa_unlikely(node->reverse_hash > reverse_hash)) { node = next = NULL; break; } next = rcu_dereference(node->next); assert(node == clear_flag(node)); if (caa_likely(!is_removed(next)) && !is_bucket(next) && node->reverse_hash == reverse_hash && caa_likely(match(node, key))) { break; } node = clear_flag(next); } assert(!node || !is_bucket(CMM_LOAD_SHARED(node->next))); iter->node = node; iter->next = next; } void cds_lfht_next_duplicate(struct cds_lfht *ht, cds_lfht_match_fct match, const void *key, struct cds_lfht_iter *iter) { struct cds_lfht_node *node, *next; unsigned long reverse_hash; node = iter->node; reverse_hash = node->reverse_hash; next = iter->next; node = clear_flag(next); for (;;) { if (caa_unlikely(is_end(node))) { node = next = NULL; break; } if (caa_unlikely(node->reverse_hash > reverse_hash)) { node = next = NULL; break; } next = rcu_dereference(node->next); if (caa_likely(!is_removed(next)) && !is_bucket(next) && caa_likely(match(node, key))) { break; } node = clear_flag(next); } assert(!node || !is_bucket(CMM_LOAD_SHARED(node->next))); iter->node = node; iter->next = next; } void cds_lfht_next(struct cds_lfht *ht, struct cds_lfht_iter *iter) { struct cds_lfht_node *node, *next; node = clear_flag(iter->next); for (;;) { if (caa_unlikely(is_end(node))) { node = next = NULL; break; } next = rcu_dereference(node->next); if (caa_likely(!is_removed(next)) && !is_bucket(next)) { break; } node = clear_flag(next); } assert(!node || !is_bucket(CMM_LOAD_SHARED(node->next))); iter->node = node; iter->next = next; } void cds_lfht_first(struct cds_lfht *ht, struct cds_lfht_iter *iter) { /* * Get next after first bucket node. The first bucket node is the * first node of the linked list. */ iter->next = bucket_at(ht, 0)->next; cds_lfht_next(ht, iter); } void cds_lfht_add(struct cds_lfht *ht, unsigned long hash, struct cds_lfht_node *node) { unsigned long size; node->reverse_hash = bit_reverse_ulong(hash); size = rcu_dereference(ht->size); _cds_lfht_add(ht, hash, NULL, NULL, size, node, NULL, 0); ht_count_add(ht, size, hash); } struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht, unsigned long hash, cds_lfht_match_fct match, const void *key, struct cds_lfht_node *node) { unsigned long size; struct cds_lfht_iter iter; node->reverse_hash = bit_reverse_ulong(hash); size = rcu_dereference(ht->size); _cds_lfht_add(ht, hash, match, key, size, node, &iter, 0); if (iter.node == node) ht_count_add(ht, size, hash); return iter.node; } struct cds_lfht_node *cds_lfht_add_replace(struct cds_lfht *ht, unsigned long hash, cds_lfht_match_fct match, const void *key, struct cds_lfht_node *node) { unsigned long size; struct cds_lfht_iter iter; node->reverse_hash = bit_reverse_ulong(hash); size = rcu_dereference(ht->size); for (;;) { _cds_lfht_add(ht, hash, match, key, size, node, &iter, 0); if (iter.node == node) { ht_count_add(ht, size, hash); return NULL; } if (!_cds_lfht_replace(ht, size, iter.node, iter.next, node)) return iter.node; } } int cds_lfht_replace(struct cds_lfht *ht, struct cds_lfht_iter *old_iter, unsigned long hash, cds_lfht_match_fct match, const void *key, struct cds_lfht_node *new_node) { unsigned long size; new_node->reverse_hash = bit_reverse_ulong(hash); if (!old_iter->node) return -ENOENT; if (caa_unlikely(old_iter->node->reverse_hash != new_node->reverse_hash)) return -EINVAL; if (caa_unlikely(!match(old_iter->node, key))) return -EINVAL; size = rcu_dereference(ht->size); return _cds_lfht_replace(ht, size, old_iter->node, old_iter->next, new_node); } int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node) { unsigned long size; int ret; size = rcu_dereference(ht->size); ret = _cds_lfht_del(ht, size, node); if (!ret) { unsigned long hash; hash = bit_reverse_ulong(node->reverse_hash); ht_count_del(ht, size, hash); } return ret; } int cds_lfht_is_node_deleted(struct cds_lfht_node *node) { return is_removed(CMM_LOAD_SHARED(node->next)); } static int cds_lfht_delete_bucket(struct cds_lfht *ht) { struct cds_lfht_node *node; unsigned long order, i, size; /* Check that the table is empty */ node = bucket_at(ht, 0); do { node = clear_flag(node)->next; if (!is_bucket(node)) return -EPERM; assert(!is_removed(node)); assert(!is_removal_owner(node)); } while (!is_end(node)); /* * size accessed without rcu_dereference because hash table is * being destroyed. */ size = ht->size; /* Internal sanity check: all nodes left should be buckets */ for (i = 0; i < size; i++) { node = bucket_at(ht, i); dbg_printf("delete bucket: index %lu expected hash %lu hash %lu\n", i, i, bit_reverse_ulong(node->reverse_hash)); assert(is_bucket(node->next)); } for (order = cds_lfht_get_count_order_ulong(size); (long)order >= 0; order--) cds_lfht_free_bucket_table(ht, order); return 0; } /* * Should only be called when no more concurrent readers nor writers can * possibly access the table. */ int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr) { int ret; if (ht->flags & CDS_LFHT_AUTO_RESIZE) { /* Cancel ongoing resize operations. */ _CMM_STORE_SHARED(ht->in_progress_destroy, 1); /* Wait for in-flight resize operations to complete */ urcu_workqueue_flush_queued_work(cds_lfht_workqueue); } ret = cds_lfht_delete_bucket(ht); if (ret) return ret; free_split_items_count(ht); if (attr) *attr = ht->resize_attr; ret = pthread_mutex_destroy(&ht->resize_mutex); if (ret) ret = -EBUSY; if (ht->flags & CDS_LFHT_AUTO_RESIZE) cds_lfht_fini_worker(ht->flavor); poison_free(ht); return ret; } void cds_lfht_count_nodes(struct cds_lfht *ht, long *approx_before, unsigned long *count, long *approx_after) { struct cds_lfht_node *node, *next; unsigned long nr_bucket = 0, nr_removed = 0; *approx_before = 0; if (ht->split_count) { int i; for (i = 0; i < split_count_mask + 1; i++) { *approx_before += uatomic_read(&ht->split_count[i].add); *approx_before -= uatomic_read(&ht->split_count[i].del); } } *count = 0; /* Count non-bucket nodes in the table */ node = bucket_at(ht, 0); do { next = rcu_dereference(node->next); if (is_removed(next)) { if (!is_bucket(next)) (nr_removed)++; else (nr_bucket)++; } else if (!is_bucket(next)) (*count)++; else (nr_bucket)++; node = clear_flag(next); } while (!is_end(node)); dbg_printf("number of logically removed nodes: %lu\n", nr_removed); dbg_printf("number of bucket nodes: %lu\n", nr_bucket); *approx_after = 0; if (ht->split_count) { int i; for (i = 0; i < split_count_mask + 1; i++) { *approx_after += uatomic_read(&ht->split_count[i].add); *approx_after -= uatomic_read(&ht->split_count[i].del); } } } /* called with resize mutex held */ static void _do_cds_lfht_grow(struct cds_lfht *ht, unsigned long old_size, unsigned long new_size) { unsigned long old_order, new_order; old_order = cds_lfht_get_count_order_ulong(old_size); new_order = cds_lfht_get_count_order_ulong(new_size); dbg_printf("resize from %lu (order %lu) to %lu (order %lu) buckets\n", old_size, old_order, new_size, new_order); assert(new_size > old_size); init_table(ht, old_order + 1, new_order); } /* called with resize mutex held */ static void _do_cds_lfht_shrink(struct cds_lfht *ht, unsigned long old_size, unsigned long new_size) { unsigned long old_order, new_order; new_size = max(new_size, MIN_TABLE_SIZE); old_order = cds_lfht_get_count_order_ulong(old_size); new_order = cds_lfht_get_count_order_ulong(new_size); dbg_printf("resize from %lu (order %lu) to %lu (order %lu) buckets\n", old_size, old_order, new_size, new_order); assert(new_size < old_size); /* Remove and unlink all bucket nodes to remove. */ fini_table(ht, new_order + 1, old_order); } /* called with resize mutex held */ static void _do_cds_lfht_resize(struct cds_lfht *ht) { unsigned long new_size, old_size; /* * Resize table, re-do if the target size has changed under us. */ do { if (CMM_LOAD_SHARED(ht->in_progress_destroy)) break; ht->resize_initiated = 1; old_size = ht->size; new_size = CMM_LOAD_SHARED(ht->resize_target); if (old_size < new_size) _do_cds_lfht_grow(ht, old_size, new_size); else if (old_size > new_size) _do_cds_lfht_shrink(ht, old_size, new_size); ht->resize_initiated = 0; /* write resize_initiated before read resize_target */ cmm_smp_mb(); } while (ht->size != CMM_LOAD_SHARED(ht->resize_target)); } static unsigned long resize_target_grow(struct cds_lfht *ht, unsigned long new_size) { return _uatomic_xchg_monotonic_increase(&ht->resize_target, new_size); } static void resize_target_update_count(struct cds_lfht *ht, unsigned long count) { count = max(count, MIN_TABLE_SIZE); count = min(count, ht->max_nr_buckets); uatomic_set(&ht->resize_target, count); } void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size) { resize_target_update_count(ht, new_size); CMM_STORE_SHARED(ht->resize_initiated, 1); mutex_lock(&ht->resize_mutex); _do_cds_lfht_resize(ht); mutex_unlock(&ht->resize_mutex); } static void do_resize_cb(struct urcu_work *work) { struct resize_work *resize_work = caa_container_of(work, struct resize_work, work); struct cds_lfht *ht = resize_work->ht; ht->flavor->register_thread(); mutex_lock(&ht->resize_mutex); _do_cds_lfht_resize(ht); mutex_unlock(&ht->resize_mutex); ht->flavor->unregister_thread(); poison_free(work); } static void __cds_lfht_resize_lazy_launch(struct cds_lfht *ht) { struct resize_work *work; /* Store resize_target before read resize_initiated */ cmm_smp_mb(); if (!CMM_LOAD_SHARED(ht->resize_initiated)) { if (CMM_LOAD_SHARED(ht->in_progress_destroy)) { return; } work = malloc(sizeof(*work)); if (work == NULL) { dbg_printf("error allocating resize work, bailing out\n"); return; } work->ht = ht; urcu_workqueue_queue_work(cds_lfht_workqueue, &work->work, do_resize_cb); CMM_STORE_SHARED(ht->resize_initiated, 1); } } static void cds_lfht_resize_lazy_grow(struct cds_lfht *ht, unsigned long size, int growth) { unsigned long target_size = size << growth; target_size = min(target_size, ht->max_nr_buckets); if (resize_target_grow(ht, target_size) >= target_size) return; __cds_lfht_resize_lazy_launch(ht); } /* * We favor grow operations over shrink. A shrink operation never occurs * if a grow operation is queued for lazy execution. A grow operation * cancels any pending shrink lazy execution. */ static void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size, unsigned long count) { if (!(ht->flags & CDS_LFHT_AUTO_RESIZE)) return; count = max(count, MIN_TABLE_SIZE); count = min(count, ht->max_nr_buckets); if (count == size) return; /* Already the right size, no resize needed */ if (count > size) { /* lazy grow */ if (resize_target_grow(ht, count) >= count) return; } else { /* lazy shrink */ for (;;) { unsigned long s; s = uatomic_cmpxchg(&ht->resize_target, size, count); if (s == size) break; /* no resize needed */ if (s > size) return; /* growing is/(was just) in progress */ if (s <= count) return; /* some other thread do shrink */ size = s; } } __cds_lfht_resize_lazy_launch(ht); } static void cds_lfht_before_fork(void *priv) { if (cds_lfht_workqueue_atfork_nesting++) return; mutex_lock(&cds_lfht_fork_mutex); if (!cds_lfht_workqueue) return; urcu_workqueue_pause_worker(cds_lfht_workqueue); } static void cds_lfht_after_fork_parent(void *priv) { if (--cds_lfht_workqueue_atfork_nesting) return; if (!cds_lfht_workqueue) goto end; urcu_workqueue_resume_worker(cds_lfht_workqueue); end: mutex_unlock(&cds_lfht_fork_mutex); } static void cds_lfht_after_fork_child(void *priv) { if (--cds_lfht_workqueue_atfork_nesting) return; if (!cds_lfht_workqueue) goto end; urcu_workqueue_create_worker(cds_lfht_workqueue); end: mutex_unlock(&cds_lfht_fork_mutex); } static struct urcu_atfork cds_lfht_atfork = { .before_fork = cds_lfht_before_fork, .after_fork_parent = cds_lfht_after_fork_parent, .after_fork_child = cds_lfht_after_fork_child, }; /* Block all signals to ensure we don't disturb the application. */ static void cds_lfht_worker_init(struct urcu_workqueue *workqueue, void *priv) { int ret; sigset_t mask; /* Block signal for entire process, so only our thread processes it. */ ret = sigfillset(&mask); if (ret) urcu_die(errno); ret = pthread_sigmask(SIG_BLOCK, &mask, NULL); if (ret) urcu_die(ret); } static void cds_lfht_init_worker(const struct rcu_flavor_struct *flavor) { flavor->register_rculfhash_atfork(&cds_lfht_atfork); mutex_lock(&cds_lfht_fork_mutex); if (cds_lfht_workqueue_user_count++) goto end; cds_lfht_workqueue = urcu_workqueue_create(0, -1, NULL, NULL, cds_lfht_worker_init, NULL, NULL, NULL, NULL, NULL); end: mutex_unlock(&cds_lfht_fork_mutex); } static void cds_lfht_fini_worker(const struct rcu_flavor_struct *flavor) { mutex_lock(&cds_lfht_fork_mutex); if (--cds_lfht_workqueue_user_count) goto end; urcu_workqueue_destroy(cds_lfht_workqueue); cds_lfht_workqueue = NULL; end: mutex_unlock(&cds_lfht_fork_mutex); flavor->unregister_rculfhash_atfork(&cds_lfht_atfork); }