#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;
// 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", GET_PTR(e_key)->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);
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);
+ 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.
// 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
+ 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
}
}
}
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);
+ 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 old_ht2_e_value = SYNC_CAS(&ht2_e->value, DOES_NOT_EXIST, value);
//
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("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, 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("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.
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;
}
}
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);
int num_copied = 0;
int x = hti->scan;
+ 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) {
// 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;
projects / nbds / blobdiff