#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
typedef struct ht_entry {
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);
// 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 %p 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
uint64_t e_key = e->key;
if (e_key == DOES_NOT_EXIST) {
- TRACE("h0", "hti_lookup: empty entry %p found", e, 0);
+ 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 value %p", e, e->value);
- TRACE("h0", "hti_lookup: entry key %p len %llu", GET_PTR(e_key)->val,
- GET_PTR(e_key)->len);
+ 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;
}
}
}
// 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;
}
// Allocate the new table and attempt to install it.
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);
// 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 <ht1_e> (which must be an entry in <ht1>) to <ht2>.
// 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);
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; // <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.
+ // 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;
}
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.
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)) {
+ 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); // 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 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
}
//
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);
+ 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);
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 %p in entry %p", key, 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;
}
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 %p expected by caller not found; found value %p",
+ 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)) {
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);
+ 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);
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);
+ TRACE("h1", "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);
+ TRACE("h1", "ht_compare_and_set: help copy panic", 0, 0);
// scan the whole table
limit = (1 << hti->scale);
e = hti->table;
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