#include "ht.h"
#include "murmur.h"
#include "mem.h"
-#include "rcu.h"
#define COPIED_VALUE (-1)
#define TOMBSTONE STRIP_TAG(COPIED_VALUE)
#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
+
typedef struct ht_entry {
- int64_t key;
- int64_t value;
+ uint64_t key;
+ uint64_t value;
} entry_t;
typedef struct string {
} hash_table_i_t;
static int hti_copy_entry
- (hash_table_i_t *old_hti, volatile entry_t *e, uint32_t e_key_hash, hash_table_i_t *new_hti);
+ (hash_table_i_t *ht1, volatile entry_t *e, uint32_t e_key_hash, hash_table_i_t *ht2);
// Choose the next bucket to probe using the high-order bits of <key_hash>.
static inline int get_next_ndx(int old_ndx, uint32_t key_hash, int ht_scale) {
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;
- const string_t *a_key = (string_t *)(a & MASK(48)); // low-order 48 bits is a pointer
+ const string_t *a_key = GET_PTR(a);
assert(a_key);
return a_key->len == b_len && memcmp(a_key->val, b_value, b_len) == 0;
}
// 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("h0", "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("h0", "hti_lookup: empty entry %p found", e, 0);
+ *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",
- ((string_t *)(e_key & MASK(48)))->val, e->value);
+ TRACE("h0", "hti_lookup: entry %p found value %p", e, e->value);
+ TRACE("h0", "hti_lookup: entry key %p len %llu", GET_PTR(e_key)->val,
+ GET_PTR(e_key)->len);
return e;
}
}
//
// Initiates a copy by creating a larger hash_table_i_t and installing it in <hti->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);
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);
+ TRACE("h0", "hti_start_copy: new hti %p scale %llu", next->scale, next->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);
TRACE("h0", "hti_start_copy: new hti is %p", next, 0);
}
-// Copy the key and value stored in <old_e> (which must be an entry in <old_hti>) to <new_hti>.
+// Copy the key and value stored in <ht1_e> (which must be an entry in <ht1>) to <ht2>.
//
-// Return 1 unless <old_e> is already copied (then return 0), so the caller can account for the total
+// Return 1 unless <ht1_e> 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 (hash_table_i_t *old_hti, volatile entry_t *old_e, uint32_t key_hash,
- hash_table_i_t *new_hti) {
- TRACE("h0", "hti_copy_entry(copy entry from %p to %p)", old_hti, new_hti);
- assert(old_hti);
- assert(old_hti->next);
- assert(new_hti);
- assert(old_e >= old_hti->table && old_e < old_hti->table + (1 << old_hti->scale));
-
- int64_t old_e_value = old_e->value;
- TRACE("h0", "hti_copy_entry: entry %p current value %p", old_e, old_e_value);
- if (EXPECT_FALSE(old_e_value == COPIED_VALUE))
+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);
+ 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;
+ TRACE("h0", "hti_copy_entry: entry %p current value %p", ht1_e, ht1_e_value);
+ if (EXPECT_FALSE(ht1_e_value == COPIED_VALUE))
return FALSE; // already copied
// Kill empty entries.
- if (EXPECT_FALSE(old_e_value == DOES_NOT_EXIST)) {
- old_e_value = SYNC_CAS(&old_e->value, DOES_NOT_EXIST, COPIED_VALUE);
- if (old_e_value == DOES_NOT_EXIST) {
+ 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);
return TRUE;
}
- if (old_e_value == COPIED_VALUE) {
+ if (ht1_e_value == COPIED_VALUE) {
TRACE("h0", "hti_copy_entry: lost race to kill empty entry in old hti", 0, 0);
return FALSE; // another thread beat us to it
}
}
// Tag the value in the old entry to indicate a copy is in progress.
- old_e_value = SYNC_FETCH_AND_OR(&old_e->value, TAG_VALUE(0));
- TRACE("h0", "hti_copy_entry: tagged the value %p in old entry %p", old_e_value, old_e);
- if (old_e_value == COPIED_VALUE)
+ 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)
return FALSE; // <value> 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.
assert(COPIED_VALUE == TAG_VALUE(TOMBSTONE));
- if (old_e_value == TOMBSTONE) {
- nbd_free((string_t *)(old_e->key & MASK(48)));
+ if (ht1_e_value == TOMBSTONE) {
+ nbd_defer_free(GET_PTR(ht1_e->key));
return TRUE;
}
- old_e_value = STRIP_TAG(old_e_value);
// Install the key in the new table.
- uint64_t old_e_key = old_e->key;
- string_t *key = (string_t *)(old_e_key & MASK(48));
- TRACE("h0", "hti_copy_entry: key %p is %s", old_e_key, key->val);
+ 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 value %p", key, value);
// We use 0 to indicate that <key_hash> isn't initiallized. Occasionally the <key_hash> 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->val, key->len);
+ key_hash = murmur32(key_string->val, key_string->len);
}
int is_empty;
- volatile entry_t *new_e = hti_lookup(new_hti, key_hash, key->val, key->len, &is_empty);
+ volatile entry_t *ht2_e = hti_lookup(ht2, key_hash, key_string->val, key_string->len, &is_empty);
// it is possible that there is not any room in the new table either
- if (EXPECT_FALSE(new_e == NULL)) {
- hti_start_copy(new_hti); // initiate nested copy, if not already started
- return hti_copy_entry(old_hti, old_e, key_hash, new_hti->next); // recursive tail-call
+ if (EXPECT_FALSE(ht2_e == NULL)) {
+ 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 new_e_key = SYNC_CAS(&new_e->key, DOES_NOT_EXIST, old_e_key);
- if (new_e_key != DOES_NOT_EXIST) {
+ 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",
- old_e_key, new_e_key);
- return hti_copy_entry(old_hti, old_e, key_hash, new_hti); // recursive tail-call
+ key, old_ht2_e_key);
+ return hti_copy_entry(ht1, ht1_e, key_hash, ht2); // recursive tail-call
}
}
- assert(ht_key_equals(new_e->key, key_hash, key->val, key->len));
- TRACE("h0", "hti_copy_entry: key %p installed in new old hti %p", key->val, new_hti);
+ 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 hti %p", key_string->val, ht2);
// Copy the value to the entry in the new table.
- uint64_t new_e_value = SYNC_CAS(&new_e->value, DOES_NOT_EXIST, old_e_value);
+ 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 (new_e_value == COPIED_VALUE)
- return hti_copy_entry(old_hti, old_e, key_hash, new_hti->next); // recursive tail-call
+ if (old_ht2_e_value == COPIED_VALUE)
+ return hti_copy_entry(ht1, ht1_e, key_hash, ht2->next); // recursive tail-call
// Mark the old entry as dead.
- old_e->value = COPIED_VALUE;
+ ht1_e->value = COPIED_VALUE;
// Update the count if we were the one that completed the copy.
- if (new_e_value == DOES_NOT_EXIST) {
- TRACE("h0", "hti_copy_entry: value %p installed in new hti %p", old_e_value, new_hti);
- SYNC_ADD(&old_hti->count, -1);
- SYNC_ADD(&new_hti->count, 1);
+ if (old_ht2_e_value == DOES_NOT_EXIST) {
+ TRACE("h0", "hti_copy_entry: value %p installed in new hti %p", value, ht2);
+ 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",
- old_e_value, new_e_value);
+ value, old_ht2_e_value);
return FALSE; // another thread completed the copy
}
// real value matches (i.e. not a TOMBSTONE or DOES_NOT_EXIST) as long as <key> is in the table. If
// <expected> is HT_EXPECT_WHATEVER then skip the test entirely.
//
-static int64_t hti_compare_and_set (hash_table_i_t *hti, uint32_t key_hash, const char *key_val,
- uint32_t key_len, int64_t expected, int64_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);
+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 %p", hti, key_val);
+ TRACE("h0", "hti_compare_and_set: new value %p expected old value %p", new, expected);
assert(hti);
assert(new != DOES_NOT_EXIST && !IS_TAGGED(new));
assert(key_val);
// There is no room for <key>, grow the table and try again.
if (e == NULL) {
- hti_start_copy(hti);
+ if (hti->next == NULL) {
+ hti_start_copy(hti);
+ }
return COPIED_VALUE;
}
if (new == TOMBSTONE)
return DOES_NOT_EXIST;
- // allocate <key>.
+ // Allocate <key>.
string_t *key = nbd_malloc(sizeof(uint32_t) + key_len);
key->len = key_len;
memcpy(key->val, key_val, key_len);
- // CAS <key> into the table.
- uint64_t e_key = SYNC_CAS(&e->key, DOES_NOT_EXIST, ((uint64_t)(key_hash >> 16) << 48) | (uint64_t)key);
+ // Combine <key> 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, e_key & MASK(48));
- 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("h0", "hti_compare_and_set: installed key %p in entry %p", key, e);
}
// If the entry is in the middle of a copy, the copy must be completed first.
- int64_t e_value = e->value;
+ 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);
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("h0", "hti_compare_and_set: value %p expected by caller not found; found value %p",
+ expected, e_value);
return e_value;
}
}
}
//
-static int64_t hti_get (hash_table_i_t *hti, uint32_t key_hash, const char *key_val, uint32_t key_len) {
+static uint64_t hti_get (hash_table_i_t *hti, uint32_t key_hash, const char *key_val, uint32_t key_len) {
assert(key_val);
int is_empty;
return DOES_NOT_EXIST;
// If the entry is being copied, finish the copy and retry on the next table.
- int64_t e_value = e->value;
+ 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 hash_table_i_t *)hti)->next);
}
//
-int64_t ht_get (hash_table_t *ht, const char *key_val, uint32_t key_len) {
+uint64_t ht_get (hash_table_t *ht, const char *key_val, uint32_t key_len) {
return hti_get(*ht, murmur32(key_val, key_len), key_val, key_len);
}
//
-int64_t ht_compare_and_set (hash_table_t *ht, const char *key_val, uint32_t key_len,
- int64_t expected_val, int64_t new_val) {
+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("h0", "ht_compare_and_set: key %p len %u", key_val, key_len);
+ TRACE("h0", "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);
// Help with an ongoing copy.
if (EXPECT_FALSE(hti->next != NULL)) {
-
- // 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.
+ volatile entry_t *e;
+ uint64_t limit;
+ int num_copied = 0;
int x = hti->scan;
- hti->scan = x + ENTRIES_PER_COPY_CHUNK;
- // <hti->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.
- volatile entry_t *e = hti->table + (x & MASK(hti->scale));
+ TRACE("h0", "ht_compare_and_set: help copy. scan is %llu, size is %llu", x, 1<<hti->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;
+
+ // <hti->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("h0", "ht_compare_and_set: help copy panic", 0, 0);
+ // scan the whole table
+ limit = (1 << hti->scale);
+ e = hti->table;
+ }
// Copy the entries
- int num_copied = 0, i;
- for (i = 0; i < ENTRIES_PER_COPY_CHUNK; ++i) {
+ 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.
- while (hti->num_entries_copied == (1 << hti->scale)) {
- assert(hti->next);
- if (SYNC_CAS(ht, hti, hti->next) == hti) {
- nbd_defer_free(hti);
+ // Dispose of fully copied tables.
+ if (hti->num_entries_copied == (1 << hti->scale) || panic) {
+ assert(hti->next);
+ if (SYNC_CAS(ht, hti, hti->next) == hti) {
+ nbd_defer_free(hti);
+ }
}
- hti = *ht;
}
- int64_t old_val;
+ uint64_t old_val;
uint32_t key_hash = murmur32(key_val, key_len);
while ((old_val = hti_compare_and_set(hti, key_hash, key_val, key_len, expected_val, new_val))
== COPIED_VALUE) {
// Remove the value in <ht> associated with <key_val>. Returns the value removed, or
// DOES_NOT_EXIST if there was no value for that key.
-int64_t ht_remove (hash_table_t *ht, const char *key_val, uint32_t key_len) {
+uint64_t ht_remove (hash_table_t *ht, const char *key_val, uint32_t key_len) {
hash_table_i_t *hti = *ht;
- int64_t val;
+ uint64_t val;
uint32_t key_hash = murmur32(key_val, key_len);
do {
val = hti_compare_and_set(hti, key_hash, key_val, key_len, HT_EXPECT_WHATEVER, TOMBSTONE);
void ht_free (hash_table_t *ht) {
hash_table_i_t *hti = *ht;
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));
+ }
+ }
hash_table_i_t *next = hti->next;
nbd_free(hti);
hti = next;
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