X-Git-Url: https://pd.if.org/git/?p=nbds;a=blobdiff_plain;f=struct%2Fht.c;h=f444af0a3350440a3355b6daed1c8e28199cc50c;hp=2eb376e4fd3d99f42505e85a1e0508eef06a3aeb;hb=d61d7ffdfa8fab555a5086e61d2e9dfe699a14b9;hpb=010e49988a8b12f78053c387b3798763b4e8df18 diff --git a/struct/ht.c b/struct/ht.c index 2eb376e..f444af0 100644 --- a/struct/ht.c +++ b/struct/ht.c @@ -17,15 +17,7 @@ #include "murmur.h" #include "mem.h" -#define COPIED_VALUE (-1) -#define TOMBSTONE STRIP_TAG(COPIED_VALUE) - -#define ENTRIES_PER_BUCKET (CACHE_LINE_SIZE/sizeof(entry_t)) -#define ENTRIES_PER_COPY_CHUNK (ENTRIES_PER_BUCKET * 2) -#define MIN_SCALE (__builtin_ctz(ENTRIES_PER_BUCKET) + 2) // min 4 buckets -#define MAX_BUCKETS_TO_PROBE 250 - -#define GET_PTR(x) (string_t *)((x) & MASK(48)) // low-order 48 bits is a pointer to a string_t +#define GET_PTR(x) ((string_t *)((x) & MASK(48))) // low-order 48 bits is a pointer to a string_t typedef struct ht_entry { uint64_t key; @@ -49,6 +41,14 @@ typedef struct hash_table_i { int scan; } hash_table_i_t; +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 (hash_table_i_t *ht1, volatile entry_t *e, uint32_t e_key_hash, hash_table_i_t *ht2); @@ -81,33 +81,30 @@ static inline int ht_key_equals (uint64_t a, uint32_t b_hash, const char *b_valu // 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 (hash_table_i_t *hti, uint32_t key_hash, const char *key_val, uint32_t key_len, int *is_empty) { - TRACE("h0", "hti_lookup(key \"%s\" in hti %p)", key_val, hti); + TRACE("h2", "hti_lookup(key %p in hti %p)", key_val, hti); *is_empty = 0; // Probe one cache line at a time int ndx = key_hash & MASK(hti->scale); // the first entry to search - int i; - for (i = 0; i < hti->max_probe; ++i) { + 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. - int j; - for (j = 0; j < ENTRIES_PER_BUCKET; ++j) { + 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("h0", "hti_lookup: empty entry %p found on probe %d", e, i*ENTRIES_PER_BUCKET+j+1); - // we tag the pointer so the caller can avoid an expensive ht_key_equals() - *is_empty = 1; + TRACE("h1", "hti_lookup: entry %p for key \"%s\" is empty", e, GET_PTR(e_key)->val); + *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_val, key_len)) { - TRACE("h0", "hti_lookup: entry %p found on probe %d", e, i*ENTRIES_PER_BUCKET+j+1); - TRACE("h0", "hti_lookup: with key \"%s\" value %p", GET_PTR(e_key)->val, e->value); + TRACE("h1", "hti_lookup: entry %p key \"%s\"", e, GET_PTR(e_key)->val); + TRACE("h2", "hti_lookup: entry key len %llu, value %p", GET_PTR(e_key)->len, e->value); return e; } } @@ -116,7 +113,7 @@ static volatile entry_t *hti_lookup (hash_table_i_t *hti, uint32_t key_hash, con } // maximum number of probes exceeded - TRACE("h0", "hti_lookup: maximum number of probes exceeded returning 0x0", 0, 0); + TRACE("h1", "hti_lookup: maximum number of probes exceeded returning 0x0", 0, 0); return NULL; } @@ -153,9 +150,7 @@ static hash_table_i_t *hti_alloc (hash_table_t *parent, int scale) { // // Initiates a copy by creating a larger hash_table_i_t and installing it in next>. static void hti_start_copy (hash_table_i_t *hti) { - TRACE("h0", "hti_start_copy(hti %p hti->next %p)", hti, hti->next); - if (hti->next) - return; // another thread beat us to it + 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); @@ -164,15 +159,15 @@ static void hti_start_copy (hash_table_i_t *hti) { 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. - hash_table_i_t *next = hti_alloc(hti->ht, hti->scale + 1); + hash_table_i_t *next = hti_alloc(hti->ht, new_scale); hash_table_i_t *old_next = SYNC_CAS(&hti->next, NULL, next); if (old_next != NULL) { - TRACE("h0", "hti_start_copy: lost race to install new hti; found %p", old_next, 0); // 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 is %p", next, 0); + 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 . @@ -181,7 +176,7 @@ static void hti_start_copy (hash_table_i_t *hti) { // number of entries left to copy. static int hti_copy_entry (hash_table_i_t *ht1, volatile entry_t *ht1_e, uint32_t key_hash, hash_table_i_t *ht2) { - TRACE("h0", "hti_copy_entry(copy entry from %p to %p)", ht1, ht2); + TRACE("h2", "hti_copy_entry: entry %p to table %p", ht1_e, ht2); assert(ht1); assert(ht1->next); assert(ht2); @@ -189,35 +184,40 @@ static int hti_copy_entry (hash_table_i_t *ht1, volatile entry_t *ht1_e, uint32_ assert(key_hash == 0 || (key_hash >> 16) == (ht1_e->key >> 48)); uint64_t ht1_e_value = ht1_e->value; - TRACE("h0", "hti_copy_entry: entry %p current value %p", ht1_e, ht1_e_value); - if (EXPECT_FALSE(ht1_e_value == COPIED_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("h0", "hti_copy_entry: old entry killed", 0, 0); + 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 in old hti", 0, 0); + 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 in old hti; " - "the entry is now being used", 0, 0); + 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("h0", "hti_copy_entry: tagged the value %p in old entry %p", ht1_e_value, ht1_e); - if (ht1_e_value == COPIED_VALUE) + 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. + } - // Deleted entries don't need to be installed into to the new table, but their keys do need to - // be freed. + // 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; } @@ -226,7 +226,6 @@ static int hti_copy_entry (hash_table_i_t *ht1, volatile entry_t *ht1_e, uint32_ uint64_t key = ht1_e->key; string_t *key_string = GET_PTR(key); uint64_t value = STRIP_TAG(ht1_e_value); - TRACE("h0", "hti_copy_entry: key %p is %s", key, key_string->val); // 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. @@ -236,10 +235,14 @@ static int hti_copy_entry (hash_table_i_t *ht1, volatile entry_t *ht1_e, uint32_ int is_empty; volatile entry_t *ht2_e = hti_lookup(ht2, key_hash, key_string->val, 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)) { - hti_start_copy(ht2); // initiate nested copy, if not already started + 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 } @@ -252,28 +255,28 @@ static int hti_copy_entry (hash_table_i_t *ht1, volatile entry_t *ht1_e, uint32_ return hti_copy_entry(ht1, ht1_e, key_hash, ht2); // recursive tail-call } } - assert(ht_key_equals(ht2_e->key, key_hash, key_string->val, key_string->len)); - TRACE("h0", "hti_copy_entry: key %p installed in new old hti %p", key_string->val, ht2); // 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) + 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: value %p installed in new hti %p", value, ht2); + TRACE("h0", "hti_copy_entry: key \"%s\" value %p copied to new entry", key_string->val, value); SYNC_ADD(&ht1->count, -1); SYNC_ADD(&ht2->count, 1); return TRUE; } - TRACE("h0", "hti_copy_entry: lost race to CAS value %p in new hti; found %p", + 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 } @@ -294,8 +297,8 @@ static int hti_copy_entry (hash_table_i_t *ht1, volatile entry_t *ht1_e, uint32_ // static uint64_t hti_compare_and_set (hash_table_i_t *hti, uint32_t key_hash, const char *key_val, uint32_t key_len, uint64_t expected, uint64_t new) { - TRACE("h0", "hti_compare_and_set(hti %p key \"%s\")", hti, key_val); - TRACE("h0", "hti_compare_and_set(new value %p; caller expects value %p)", new, expected); + TRACE("h1", "hti_compare_and_set: hti %p key %p", hti, key_val); + TRACE("h1", "hti_compare_and_set: value %p expect %p", new, expected); assert(hti); assert(new != DOES_NOT_EXIST && !IS_TAGGED(new)); assert(key_val); @@ -305,7 +308,9 @@ static uint64_t hti_compare_and_set (hash_table_i_t *hti, uint32_t key_hash, con // There is no room for , grow the table and try again. if (e == NULL) { - hti_start_copy(hti); + if (hti->next == NULL) { + hti_start_copy(hti); + } return COPIED_VALUE; } @@ -319,32 +324,39 @@ static uint64_t hti_compare_and_set (hash_table_i_t *hti, uint32_t key_hash, con if (new == TOMBSTONE) return DOES_NOT_EXIST; - // allocate . + // Allocate . string_t *key = nbd_malloc(sizeof(uint32_t) + key_len); key->len = key_len; memcpy(key->val, key_val, key_len); - // CAS into the table. - uint64_t e_key = SYNC_CAS(&e->key, DOES_NOT_EXIST, ((uint64_t)(key_hash >> 16) << 48) | (uint64_t)key); + // 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: key in entry %p is \"%s\"", e, GET_PTR(e_key)->val); - TRACE("h0", "hti_compare_and_set: lost race to install key \"%s\" in %p", key->val, e); + 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_val, key_len, expected, new); // tail-call } - TRACE("h0", "hti_compare_and_set: installed key \"%s\" in entry %p", key_val, e); + 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)->val, e); + // If the entry is in the middle of a copy, the copy must be completed first. uint64_t e_value = e->value; - TRACE("h0", "hti_compare_and_set: value in entry %p is %p", e, e_value); if (EXPECT_FALSE(IS_TAGGED(e_value))) { - int did_copy = hti_copy_entry(hti, e, key_hash, ((volatile hash_table_i_t *)hti)->next); - if (did_copy) { - SYNC_ADD(&hti->num_entries_copied, 1); + if (e_value != COPIED_VALUE) { + int did_copy = hti_copy_entry(hti, e, key_hash, ((volatile hash_table_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; } @@ -352,12 +364,18 @@ static uint64_t hti_compare_and_set (hash_table_i_t *hti, uint32_t key_hash, con int old_existed = (e_value != TOMBSTONE && e_value != DOES_NOT_EXIST); if (EXPECT_FALSE(expected != HT_EXPECT_WHATEVER && expected != e_value)) { if (EXPECT_FALSE(expected != (old_existed ? HT_EXPECT_EXISTS : HT_EXPECT_NOT_EXISTS))) { - TRACE("h0", "hti_compare_and_set: value expected by caller for key \"%s\" not found; " - "found value %p", key_val, e_value); + 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)) { @@ -420,6 +438,8 @@ uint64_t ht_get (hash_table_t *ht, const char *key_val, uint32_t key_len) { uint64_t ht_compare_and_set (hash_table_t *ht, const char *key_val, uint32_t key_len, uint64_t expected_val, uint64_t new_val) { + TRACE("h2", "ht_compare_and_set: key %p len %u", key_val, key_len); + TRACE("h2", "ht_compare_and_set: expected val %p new val %p", expected_val, new_val); assert(key_val); assert(!IS_TAGGED(new_val) && new_val != DOES_NOT_EXIST); @@ -432,6 +452,7 @@ uint64_t ht_compare_and_set (hash_table_t *ht, const char *key_val, uint32_t key 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) { @@ -446,6 +467,7 @@ uint64_t ht_compare_and_set (hash_table_t *ht, const char *key_val, uint32_t key // 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;