X-Git-Url: https://pd.if.org/git/?p=nbds;a=blobdiff_plain;f=struct%2Fhashtable.c;fp=struct%2Fhashtable.c;h=0000000000000000000000000000000000000000;hp=5406d4242c038160047df62eb9ca43682f2e3289;hb=025017478bb385da88a6b185849c8bcffeb2e2aa;hpb=2d93f3b29622488bde80b6cd18661fd7eb603eee diff --git a/struct/hashtable.c b/struct/hashtable.c deleted file mode 100644 index 5406d42..0000000 --- a/struct/hashtable.c +++ /dev/null @@ -1,548 +0,0 @@ -/* - * Written by Josh Dybnis and released to the public domain, as explained at - * http://creativecommons.org/licenses/publicdomain - * - * C implementation of Cliff Click's lock-free hash table from - * http://www.azulsystems.com/events/javaone_2008/2008_CodingNonBlock.pdf - * http://sourceforge.net/projects/high-scale-lib - * - * Note: This is code uses synchronous atomic operations because that is all that x86 provides. - * Every atomic operation is also an implicit full memory barrier. The upshot is that it simplifies - * the code a bit, but it won't be as fast as it could be on platforms like SPARC that provide - * weaker operations which would still do the job. - */ - -#include "common.h" -#include "murmur.h" -#include "mem.h" -#include "struct.h" -#include "nstring.h" - -#define GET_PTR(x) ((nstring_t *)((x) & MASK(48))) // low-order 48 bits is a pointer to a nstring_t - -typedef struct ht_entry { - uint64_t key; // ptr to nstring_t - uint64_t value; -} entry_t; - -typedef struct hti { - volatile entry_t *table; - hashtable_t *ht; // parent ht; - struct hti *next; - struct hti *next_free; - unsigned int scale; - int max_probe; - int count; // TODO: make these counters distributed - int num_entries_copied; - int scan; -} hashtable_i_t; - -struct ht { - hashtable_i_t *hti; -}; - -static const uint64_t COPIED_VALUE = -1; -static const uint64_t TOMBSTONE = STRIP_TAG(-1); - -static const unsigned ENTRIES_PER_BUCKET = CACHE_LINE_SIZE/sizeof(entry_t); -static const unsigned ENTRIES_PER_COPY_CHUNK = CACHE_LINE_SIZE/sizeof(entry_t)*2; -static const unsigned MIN_SCALE = 4; // min 16 entries (4 buckets) -static const unsigned MAX_BUCKETS_TO_PROBE = 250; - -static int hti_copy_entry (hashtable_i_t *ht1, volatile entry_t *e, uint32_t e_key_hash, hashtable_i_t *ht2); - -// Choose the next bucket to probe using the high-order bits of . -static inline int get_next_ndx(int old_ndx, uint32_t key_hash, int ht_scale) { - int incr = (key_hash >> (32 - ht_scale)); - incr += !incr; // If the increment is 0, make it 1. - return (old_ndx + incr) & MASK(ht_scale); -} - -// Compare two keys. -// -// A key is made up of two parts. The 48 low-order bits are a pointer to a null terminated string. -// The high-order 16 bits are taken from the hash of that string. The bits from the hash are used -// as a quick check to rule out non-equal keys without doing a complete string compare. -static inline int ht_key_equals (uint64_t a, uint32_t b_hash, const char *b_value, uint32_t b_len) { - if ((b_hash >> 16) != (a >> 48)) // high-order 16 bits are from the hash value - return FALSE; - return ns_cmp_raw(GET_PTR(a), b_value, b_len) == 0; -} - -// Lookup in . -// -// Return the entry that is in, or if isn't in return the entry that it would be -// in if it were inserted into . If there is no room for in then return NULL, to -// indicate that the caller should look in next>. -// -// Record if the entry being returned is empty. Otherwise the caller will have to waste time with -// ht_key_equals() to confirm that it did not lose a race to fill an empty entry. -static volatile entry_t *hti_lookup (hashtable_i_t *hti, uint32_t key_hash, const char *key_data, uint32_t key_len, int *is_empty) { - TRACE("h2", "hti_lookup(key %p in hti %p)", key_data, hti); - *is_empty = 0; - - // Probe one cache line at a time - int ndx = key_hash & MASK(hti->scale); // the first entry to search - for (int i = 0; i < hti->max_probe; ++i) { - - // The start of the bucket is the first entry in the cache line. - volatile entry_t *bucket = hti->table + (ndx & ~(ENTRIES_PER_BUCKET-1)); - - // Start searching at the indexed entry. Then loop around to the begining of the cache line. - for (int j = 0; j < ENTRIES_PER_BUCKET; ++j) { - volatile entry_t *e = bucket + ((ndx + j) & (ENTRIES_PER_BUCKET-1)); - - uint64_t e_key = e->key; - if (e_key == DOES_NOT_EXIST) { - TRACE("h1", "hti_lookup: entry %p for key \"%s\" is empty", e, GET_PTR(e_key)->data); - *is_empty = 1; // indicate an empty so the caller avoids an expensive ht_key_equals - return e; - } - - if (ht_key_equals(e_key, key_hash, key_data, key_len)) { - TRACE("h1", "hti_lookup: entry %p key \"%s\"", e, GET_PTR(e_key)->data); - TRACE("h2", "hti_lookup: entry key len %llu, value %p", GET_PTR(e_key)->len, e->value); - return e; - } - } - - ndx = get_next_ndx(ndx, key_hash, hti->scale); - } - - // maximum number of probes exceeded - TRACE("h1", "hti_lookup: maximum number of probes exceeded returning 0x0", 0, 0); - return NULL; -} - -// Allocate and initialize a hashtable_i_t with 2^ entries. -static hashtable_i_t *hti_alloc (hashtable_t *parent, int scale) { - // Include enough slop to align the actual table on a cache line boundry - size_t n = sizeof(hashtable_i_t) - + sizeof(entry_t) * (1 << scale) - + (CACHE_LINE_SIZE - 1); - hashtable_i_t *hti = (hashtable_i_t *)calloc(n, 1); - - // Align the table of hash entries on a cache line boundry. - hti->table = (entry_t *)(((uint64_t)hti + sizeof(hashtable_i_t) + (CACHE_LINE_SIZE-1)) - & ~(CACHE_LINE_SIZE-1)); - - hti->scale = scale; - - // When searching for a key probe a maximum of 1/4 of the buckets up to 1000 buckets. - hti->max_probe = ((1 << (hti->scale - 2)) / ENTRIES_PER_BUCKET) + 2; - if (hti->max_probe > MAX_BUCKETS_TO_PROBE) { - hti->max_probe = MAX_BUCKETS_TO_PROBE; - } - - hti->ht = parent; - - assert(hti->scale >= MIN_SCALE && hti->scale < 63); // size must be a power of 2 - assert(sizeof(entry_t) * ENTRIES_PER_BUCKET % CACHE_LINE_SIZE == 0); // divisible into cache - assert((size_t)hti->table % CACHE_LINE_SIZE == 0); // cache aligned - - return hti; -} - -// Called when runs out of room for new keys. -// -// Initiates a copy by creating a larger hashtable_i_t and installing it in next>. -static void hti_start_copy (hashtable_i_t *hti) { - TRACE("h0", "hti_start_copy(hti %p scale %llu)", hti, hti->scale); - - // heuristics to determine the size of the new table - uint64_t count = ht_count(hti->ht); - unsigned int new_scale = hti->scale; - new_scale += (count > (1 << (new_scale - 2))); // double size if more than 1/4 full - new_scale += (count > (1 << (new_scale - 2))); // double size again if more than 1/2 full - - // Allocate the new table and attempt to install it. - hashtable_i_t *next = hti_alloc(hti->ht, new_scale); - hashtable_i_t *old_next = SYNC_CAS(&hti->next, NULL, next); - if (old_next != NULL) { - // Another thread beat us to it. - TRACE("h0", "hti_start_copy: lost race to install new hti; found %p", old_next, 0); - nbd_free(next); - return; - } - TRACE("h0", "hti_start_copy: new hti %p scale %llu", next, next->scale); -} - -// Copy the key and value stored in (which must be an entry in ) to . -// -// Return 1 unless is already copied (then return 0), so the caller can account for the total -// number of entries left to copy. -static int hti_copy_entry (hashtable_i_t *ht1, volatile entry_t *ht1_e, uint32_t key_hash, - hashtable_i_t *ht2) { - TRACE("h2", "hti_copy_entry: entry %p to table %p", ht1_e, ht2); - assert(ht1); - assert(ht1->next); - assert(ht2); - assert(ht1_e >= ht1->table && ht1_e < ht1->table + (1 << ht1->scale)); - assert(key_hash == 0 || (key_hash >> 16) == (ht1_e->key >> 48)); - - uint64_t ht1_e_value = ht1_e->value; - if (EXPECT_FALSE(ht1_e_value == COPIED_VALUE)) { - TRACE("h1", "hti_copy_entry: entry %p already copied to table %p", ht1_e, ht2); - return FALSE; // already copied - } - - // Kill empty entries. - if (EXPECT_FALSE(ht1_e_value == DOES_NOT_EXIST)) { - uint64_t ht1_e_value = SYNC_CAS(&ht1_e->value, DOES_NOT_EXIST, COPIED_VALUE); - if (ht1_e_value == DOES_NOT_EXIST) { - TRACE("h1", "hti_copy_entry: empty entry %p killed", ht1_e, 0); - return TRUE; - } - if (ht1_e_value == COPIED_VALUE) { - TRACE("h0", "hti_copy_entry: lost race to kill empty entry %p", ht1_e, 0); - return FALSE; // another thread beat us to it - } - TRACE("h0", "hti_copy_entry: lost race to kill empty entry %p; the entry is now" - "in use and should be copied", ht1_e, 0); - } - - // Tag the value in the old entry to indicate a copy is in progress. - ht1_e_value = SYNC_FETCH_AND_OR(&ht1_e->value, TAG_VALUE(0)); - TRACE("h2", "hti_copy_entry: tagged the value %p in old entry %p", ht1_e_value, ht1_e); - if (ht1_e_value == COPIED_VALUE) { - TRACE("h1", "hti_copy_entry: entry %p already copied to table %p", ht1_e, ht2); - return FALSE; // was already copied by another thread. - } - - // The old table's deleted entries don't need to be copied to the new table, but their keys need - // to be freed. - assert(COPIED_VALUE == TAG_VALUE(TOMBSTONE)); - if (ht1_e_value == TOMBSTONE) { - TRACE("h1", "hti_copy_entry: entry %p old value was deleted, now freeing key %p", ht1_e, GET_PTR(ht1_e->key)); - nbd_defer_free(GET_PTR(ht1_e->key)); - return TRUE; - } - - // Install the key in the new table. - uint64_t key = ht1_e->key; - nstring_t *key_string = GET_PTR(key); - uint64_t value = STRIP_TAG(ht1_e_value); - - // We use 0 to indicate that isn't initiallized. Occasionally the will - // really be 0 and we will waste time recomputing it. That is rare enough that it is OK. - if (key_hash == 0) { - key_hash = murmur32(key_string->data, key_string->len); - } - - int is_empty; - volatile entry_t *ht2_e = hti_lookup(ht2, key_hash, key_string->data, key_string->len, &is_empty); - TRACE("h0", "hti_copy_entry: copy entry %p to entry %p", ht1_e, ht2_e); - - // it is possible that there is not any room in the new table either - if (EXPECT_FALSE(ht2_e == NULL)) { - TRACE("h0", "hti_copy_entry: no room in table %p copy to next table %p", ht2, ht2->next); - if (ht2->next == NULL) { - hti_start_copy(ht2); // initiate nested copy, if not already started - } - return hti_copy_entry(ht1, ht1_e, key_hash, ht2->next); // recursive tail-call - } - - // a tagged entry returned from hti_lookup() means it is either empty or has a new key - if (is_empty) { - uint64_t old_ht2_e_key = SYNC_CAS(&ht2_e->key, DOES_NOT_EXIST, key); - if (old_ht2_e_key != DOES_NOT_EXIST) { - TRACE("h0", "hti_copy_entry: lost race to CAS key %p into new entry; found %p", - key, old_ht2_e_key); - return hti_copy_entry(ht1, ht1_e, key_hash, ht2); // recursive tail-call - } - } - - // Copy the value to the entry in the new table. - uint64_t old_ht2_e_value = SYNC_CAS(&ht2_e->value, DOES_NOT_EXIST, value); - - // If there is a nested copy in progress, we might have installed the key into a dead entry. - if (old_ht2_e_value == COPIED_VALUE) { - TRACE("h0", "hti_copy_entry: nested copy in progress; copy %p to next table %p", ht2_e, ht2->next); - return hti_copy_entry(ht1, ht1_e, key_hash, ht2->next); // recursive tail-call - } - - // Mark the old entry as dead. - ht1_e->value = COPIED_VALUE; - - // Update the count if we were the one that completed the copy. - if (old_ht2_e_value == DOES_NOT_EXIST) { - TRACE("h0", "hti_copy_entry: key \"%s\" value %p copied to new entry", key_string->data, value); - SYNC_ADD(&ht1->count, -1); - SYNC_ADD(&ht2->count, 1); - return TRUE; - } - - TRACE("h0", "hti_copy_entry: lost race to install value %p in new entry; found value %p", - value, old_ht2_e_value); - return FALSE; // another thread completed the copy -} - -// Compare with the existing value associated with . If the values match then -// replace the existing value with . If is TOMBSTONE, delete the value associated with -// the key by replacing it with a TOMBSTONE. -// -// Return the previous value associated with , or DOES_NOT_EXIST if is not in the table -// or associated with a TOMBSTONE. If a copy is in progress and has been copied to the next -// table then return COPIED_VALUE. -// -// NOTE: the returned value matches iff the set succeeds -// -// Certain values of have special meaning. If is EXPECT_EXISTS then any -// real value matches (i.e. not a TOMBSTONE or DOES_NOT_EXIST) as long as is in the table. If -// is EXPECT_WHATEVER then skip the test entirely. -// -static uint64_t hti_compare_and_set (hashtable_i_t *hti, uint32_t key_hash, const char *key_data, - uint32_t key_len, uint64_t expected, uint64_t new) { - TRACE("h1", "hti_compare_and_set: hti %p key %p", hti, key_data); - TRACE("h1", "hti_compare_and_set: value %p expect %p", new, expected); - assert(hti); - assert(new != DOES_NOT_EXIST && !IS_TAGGED(new)); - assert(key_data); - - int is_empty; - volatile entry_t *e = hti_lookup(hti, key_hash, key_data, key_len, &is_empty); - - // There is no room for , grow the table and try again. - if (e == NULL) { - if (hti->next == NULL) { - hti_start_copy(hti); - } - return COPIED_VALUE; - } - - // Install in the table if it doesn't exist. - if (is_empty) { - TRACE("h0", "hti_compare_and_set: entry %p is empty", e, 0); - if (expected != EXPECT_WHATEVER && expected != EXPECT_DOES_NOT_EXIST) - return DOES_NOT_EXIST; - - // No need to do anything, is already deleted. - if (new == TOMBSTONE) - return DOES_NOT_EXIST; - - // Allocate . - nstring_t *key = ns_alloc(key_data, key_len); - - // Combine pointer with bits from its hash, CAS it into the table. - uint64_t temp = ((uint64_t)(key_hash >> 16) << 48) | (uint64_t)key; - uint64_t e_key = SYNC_CAS(&e->key, DOES_NOT_EXIST, temp); - - // Retry if another thread stole the entry out from under us. - if (e_key != DOES_NOT_EXIST) { - TRACE("h0", "hti_compare_and_set: lost race to install key %p in entry %p", key, e); - TRACE("h0", "hti_compare_and_set: found %p instead of NULL", GET_PTR(e_key), 0); - nbd_free(key); - return hti_compare_and_set(hti, key_hash, key_data, key_len, expected, new); // tail-call - } - TRACE("h2", "hti_compare_and_set: installed key %p in entry %p", key, e); - } - - TRACE("h0", "hti_compare_and_set: entry for key \"%s\" is %p", GET_PTR(e->key)->data, e); - - // If the entry is in the middle of a copy, the copy must be completed first. - uint64_t e_value = e->value; - if (EXPECT_FALSE(IS_TAGGED(e_value))) { - if (e_value != COPIED_VALUE) { - int did_copy = hti_copy_entry(hti, e, key_hash, ((volatile hashtable_i_t *)hti)->next); - if (did_copy) { - SYNC_ADD(&hti->num_entries_copied, 1); - } - TRACE("h0", "hti_compare_and_set: value in the middle of a copy, copy completed by %s", - (did_copy ? "self" : "other"), 0); - } - TRACE("h0", "hti_compare_and_set: value copied to next table, retry on next table", 0, 0); - return COPIED_VALUE; - } - - // Fail if the old value is not consistent with the caller's expectation. - int old_existed = (e_value != TOMBSTONE && e_value != DOES_NOT_EXIST); - if (EXPECT_FALSE(expected != EXPECT_WHATEVER && expected != e_value)) { - if (EXPECT_FALSE(expected != (old_existed ? EXPECT_EXISTS : EXPECT_DOES_NOT_EXIST))) { - TRACE("h1", "hti_compare_and_set: value %p expected by caller not found; found value %p", - expected, e_value); - return e_value; - } - } - - // No need to update if value is unchanged. - if ((new == TOMBSTONE && !old_existed) || e_value == new) { - TRACE("h1", "hti_compare_and_set: old value and new value were the same", 0, 0); - return e_value; - } - - // CAS the value into the entry. Retry if it fails. - uint64_t v = SYNC_CAS(&e->value, e_value, new); - if (EXPECT_FALSE(v != e_value)) { - TRACE("h0", "hti_compare_and_set: value CAS failed; expected %p found %p", e_value, v); - return hti_compare_and_set(hti, key_hash, key_data, key_len, expected, new); // recursive tail-call - } - - // The set succeeded. Adjust the value count. - if (old_existed && new == TOMBSTONE) { - SYNC_ADD(&hti->count, -1); - } else if (!old_existed && new != TOMBSTONE) { - SYNC_ADD(&hti->count, 1); - } - - // Return the previous value. - TRACE("h0", "hti_compare_and_set: CAS succeeded; old value %p new value %p", e_value, new); - return e_value; -} - -// -static uint64_t hti_get (hashtable_i_t *hti, uint32_t key_hash, const char *key_data, uint32_t key_len) { - assert(key_data); - - int is_empty; - volatile entry_t *e = hti_lookup(hti, key_hash, key_data, key_len, &is_empty); - - // When hti_lookup() returns NULL it means we hit the reprobe limit while - // searching the table. In that case, if a copy is in progress the key - // might exist in the copy. - if (EXPECT_FALSE(e == NULL)) { - if (((volatile hashtable_i_t *)hti)->next != NULL) - return hti_get(hti->next, key_hash, key_data, key_len); // recursive tail-call - return DOES_NOT_EXIST; - } - - if (is_empty) - return DOES_NOT_EXIST; - - // If the entry is being copied, finish the copy and retry on the next table. - uint64_t e_value = e->value; - if (EXPECT_FALSE(IS_TAGGED(e_value))) { - if (EXPECT_FALSE(e_value != COPIED_VALUE)) { - int did_copy = hti_copy_entry(hti, e, key_hash, ((volatile hashtable_i_t *)hti)->next); - if (did_copy) { - SYNC_ADD(&hti->num_entries_copied, 1); - } - } - return hti_get(((volatile hashtable_i_t *)hti)->next, key_hash, key_data, key_len); // tail-call - } - - return (e_value == TOMBSTONE) ? DOES_NOT_EXIST : e_value; -} - -// -uint64_t ht_get (hashtable_t *ht, const char *key_data, uint32_t key_len) { - return hti_get(ht->hti, murmur32(key_data, key_len), key_data, key_len); -} - -// -uint64_t ht_compare_and_set (hashtable_t *ht, const char *key_data, uint32_t key_len, - uint64_t expected_val, uint64_t new_val) { - - TRACE("h2", "ht_compare_and_set: key %p len %u", key_data, key_len); - TRACE("h2", "ht_compare_and_set: expected val %p new val %p", expected_val, new_val); - assert(key_data); - assert(!IS_TAGGED(new_val) && new_val != DOES_NOT_EXIST); - - hashtable_i_t *hti = ht->hti; - - // Help with an ongoing copy. - if (EXPECT_FALSE(hti->next != NULL)) { - volatile entry_t *e; - uint64_t limit; - int num_copied = 0; - int x = hti->scan; - - TRACE("h1", "ht_compare_and_set: help copy. scan is %llu, size is %llu", x, 1<scale); - // Panic if we've been around the array twice and still haven't finished the copy. - int panic = (x >= (1 << (hti->scale + 1))); - if (!panic) { - limit = ENTRIES_PER_COPY_CHUNK; - - // Reserve some entries for this thread to copy. There is a race condition here because the - // fetch and add isn't atomic, but that is ok. - hti->scan = x + ENTRIES_PER_COPY_CHUNK; - - // scan> might be larger than the size of the table, if some thread stalls while - // copying. In that case we just wrap around to the begining and make another pass through - // the table. - e = hti->table + (x & MASK(hti->scale)); - } else { - TRACE("h1", "ht_compare_and_set: help copy panic", 0, 0); - // scan the whole table - limit = (1 << hti->scale); - e = hti->table; - } - - // Copy the entries - for (int i = 0; i < limit; ++i) { - num_copied += hti_copy_entry(hti, e++, 0, hti->next); - assert(e <= hti->table + (1 << hti->scale)); - } - if (num_copied != 0) { - SYNC_ADD(&hti->num_entries_copied, num_copied); - } - - // Dispose of fully copied tables. - if (hti->num_entries_copied == (1 << hti->scale) || panic) { - assert(hti->next); - if (SYNC_CAS(&ht->hti, hti, hti->next) == hti) { - nbd_defer_free(hti); - } - } - } - - uint64_t old_val; - uint32_t key_hash = murmur32(key_data, key_len); - while ((old_val = hti_compare_and_set(hti, key_hash, key_data, key_len, expected_val, new_val)) - == COPIED_VALUE) { - assert(hti->next); - hti = hti->next; - } - - return old_val == TOMBSTONE ? DOES_NOT_EXIST : old_val; -} - -// Remove the value in associated with . Returns the value removed, or -// DOES_NOT_EXIST if there was no value for that key. -uint64_t ht_remove (hashtable_t *ht, const char *key_data, uint32_t key_len) { - hashtable_i_t *hti = ht->hti; - uint64_t val; - uint32_t key_hash = murmur32(key_data, key_len); - do { - val = hti_compare_and_set(hti, key_hash, key_data, key_len, EXPECT_WHATEVER, TOMBSTONE); - if (val != COPIED_VALUE) - return val == TOMBSTONE ? DOES_NOT_EXIST : val; - assert(hti->next); - hti = hti->next; - assert(hti); - } while (1); -} - -// Returns the number of key-values pairs in -uint64_t ht_count (hashtable_t *ht) { - hashtable_i_t *hti = ht->hti; - uint64_t count = 0; - while (hti) { - count += hti->count; - hti = hti->next; - } - return count; -} - -// Allocate and initialize a new hash table. -hashtable_t *ht_alloc (void) { - hashtable_t *ht = nbd_malloc(sizeof(hashtable_t)); - ht->hti = (hashtable_i_t *)hti_alloc(ht, MIN_SCALE); - return ht; -} - -// Free and its internal structures. -void ht_free (hashtable_t *ht) { - hashtable_i_t *hti = ht->hti; - do { - for (uint32_t i = 0; i < (1 << hti->scale); ++i) { - assert(hti->table[i].value == COPIED_VALUE || !IS_TAGGED(hti->table[i].value)); - if (hti->table[i].key != DOES_NOT_EXIST) { - nbd_free(GET_PTR(hti->table[i].key)); - } - } - hashtable_i_t *next = hti->next; - nbd_free(hti); - hti = next; - } while (hti); - nbd_free(ht); -}