#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;
--- /dev/null
+/*
+ * Written by Josh Dybnis and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+#include "common.h"
+#include "txn.h"
+#include "mem.h"
+
+#define UNDETERMINED_VERSION 0
+#define INITIAL_WRITES_SIZE 4
+
+typedef enum { TXN_RUNNING, TXN_VALIDATING, TXN_VALIDATED, TXN_ABORTED } txn_state_t;
+typedef enum { UPDATE_TYPE_PUT, UPDATE_TYPE_DELETE } update_type_t;
+
+typedef struct update_rec update_rec_t;
+
+struct update_rec {
+ update_type_t type;
+ uint64_t value;
+ uint64_t version;
+ update_rec_t *prev; // a previous update
+};
+
+typedef struct write_rec {
+ const char *key;
+ update_rec_t *rec;
+} write_rec_t;
+
+struct txn {
+ uint64_t rv;
+ uint64_t wv;
+ hash_table_t *ht;
+ write_rec_t *writes;
+ uint32_t writes_size;
+ uint32_t writes_count;
+ uint32_t writes_scan;
+ txn_access_t access;
+ txn_isolation_t isolation;
+ txn_state_t state;
+};
+
+uint64_t GlobalVersion = 1;
+uint64_t MinActiveTxnVersion = 0;
+
+static txn_state_t txn_validate (txn_t *txn);
+
+update_rec_t *alloc_update_rec (void) {
+ update_rec_t *u = (update_rec_t *)nbd_malloc(sizeof(update_rec_t));
+ memset(u, 0, sizeof(update_rec_t));
+ return u;
+}
+
+txn_t *txn_begin (txn_access_t access, txn_isolation_t isolation, hash_table_t *ht) {
+ txn_t *txn = (txn_t *)nbd_malloc(sizeof(txn_t));
+ memset(txn, 0, sizeof(txn_t));
+ txn->access = access;
+ txn->isolation = isolation;
+ txn->rv = GlobalVersion;
+ txn->wv = UNDETERMINED_VERSION;
+ txn->state = TXN_RUNNING;
+ txn->ht = ht;
+ if (isolation != TXN_READ_ONLY) {
+ txn->writes = nbd_malloc(sizeof(*txn->writes) * INITIAL_WRITES_SIZE);
+ txn->writes_size = INITIAL_WRITES_SIZE;
+ }
+ return txn;
+}
+
+// Get most recent committed version prior to our read version.
+int64_t txn_ht_get (txn_t *txn, const char *key, uint32_t key_len) {
+
+ // Iterate through update records associated with <key> to find the latest committed version.
+ // We can use the first matching version. Older updates always come later in the list.
+ update_rec_t *update = (update_rec_t *) ht_get(txn->ht, key, key_len);
+ for (; update != NULL; update = update->prev) {
+ uint64_t writer_version = update->version;
+ if (writer_version < txn->rv)
+ return update->value;
+
+ // If the version is tagged, it means that it is not a version number, but a pointer to an
+ // in progress transaction.
+ if (IS_TAGGED(update->version)) {
+ txn_t *writer = (txn_t *)STRIP_TAG(writer_version);
+
+ if (writer == txn)
+ return update->type == UPDATE_TYPE_DELETE ? DOES_NOT_EXIST : update->value;
+
+ // Skip updates from aborted transactions.
+ txn_state_t writer_state = writer->state;
+ if (EXPECT_FALSE(writer_state == TXN_ABORTED))
+ continue;
+
+ if (writer_state == TXN_VALIDATING) {
+ writer_state = txn_validate(writer);
+ }
+
+ if (writer_state == TXN_VALIDATED && writer->wv <= txn->rv && writer->wv != UNDETERMINED_VERSION)
+ return update->type == UPDATE_TYPE_DELETE ? DOES_NOT_EXIST : update->value;
+ }
+ }
+ return DOES_NOT_EXIST;
+}
+
+// Validate the updates for <key>. Validation fails for a key we have written to if there is a
+// write committed newer than our read version.
+static txn_state_t txn_ht_validate_key (txn_t *txn, const char *key, uint32_t key_len) {
+
+ update_rec_t *update = (update_rec_t *) ht_get(txn->ht, key, key_len);
+ for (; update != NULL; update = update->prev) {
+ uint64_t writer_version = update->version;
+ if (writer_version <= txn->rv)
+ return TXN_VALIDATED;
+
+ // If the version is tagged, it means it is a pointer to a transaction in progress.
+ if (IS_TAGGED(writer_version)) {
+
+ // Skip aborted transactions.
+ if (EXPECT_FALSE(writer_version == TAG_VALUE(0)))
+ continue;
+
+ // Skip our own updates.
+ txn_t *writer = (txn_t *)STRIP_TAG(writer_version);
+ if (writer == txn)
+ continue;
+
+ writer_version = writer->wv;
+ if (writer_version <= txn->rv && writer_version != UNDETERMINED_VERSION)
+ return TXN_VALIDATED;
+
+ txn_state_t writer_state = writer->state;
+ if (EXPECT_FALSE(writer_state == TXN_ABORTED))
+ continue;
+
+ // Help validate <writer> if it is a committing transaction that might cause us to
+ // abort. However, if the <writer> has a later version than us we can safely ignore its
+ // updates. This protocol ensures a deterministic resolution to every conflict, and
+ // avoids infinite ping-ponging between validating two conflicting transactions.
+ if (writer_state == TXN_VALIDATING && (writer_version < txn->wv ||
+ writer_version == UNDETERMINED_VERSION)) {
+ writer_state = txn_validate(writer);
+ }
+
+ if (writer_state == TXN_VALIDATED)
+ return TXN_ABORTED;
+ }
+
+ return TXN_ABORTED;
+ }
+
+ return TXN_VALIDATED;
+}
+
+static txn_state_t txn_validate (txn_t *txn) {
+ int i;
+ switch (txn->state) {
+
+ case TXN_VALIDATING:
+ if (txn->wv == UNDETERMINED_VERSION) {
+ uint64_t wv = SYNC_ADD(&GlobalVersion, 1);
+ SYNC_CAS(&txn->wv, UNDETERMINED_VERSION, wv);
+ }
+
+ for (i = 0; i < txn->writes_count; ++i) {
+ txn_state_t s = txn_ht_validate_key(txn, txn->writes[i].key, strlen(txn->writes[i].key));
+ if (s == TXN_ABORTED) {
+ txn->state = TXN_ABORTED;
+ break;
+ }
+ }
+ if (txn->state == TXN_VALIDATING) {
+ txn->state = TXN_VALIDATED;
+ }
+ break;
+
+ case TXN_VALIDATED:
+ case TXN_ABORTED:
+ break;
+
+ default:
+ assert(FALSE);
+ }
+
+ return txn->state;
+}
+
+void txn_abort (txn_t *txn) {
+
+ int i;
+ for (i = 0; i < txn->writes_count; ++i) {
+ update_rec_t *update = (update_rec_t *)txn->writes[i].rec;
+ update->version = TAG_VALUE(0);
+ }
+
+ nbd_defer_free(txn->writes);
+ nbd_defer_free(txn);
+}
+
+txn_state_t txn_commit (txn_t *txn) {
+
+ assert(txn->state == TXN_RUNNING);
+ txn->state = TXN_VALIDATING;
+ txn_state_t state = txn_validate(txn);
+
+ // Detach <txn> from its updates.
+ uint64_t wv = (txn->state == TXN_ABORTED) ? TAG_VALUE(0) : txn->wv;
+ int i;
+ for (i = 0; i < txn->writes_count; ++i) {
+ update_rec_t *update = (update_rec_t *)txn->writes[i].rec;
+ update->version = wv;
+ }
+
+ nbd_defer_free(txn->writes);
+ nbd_defer_free(txn);
+
+ return state;
+}
+
+void txn_ht_put (txn_t *txn, const char *key, uint32_t key_len, int64_t value) {
+
+ // create a new update record
+ update_rec_t *update = alloc_update_rec();
+ update->type = UPDATE_TYPE_PUT;
+ update->value = value;
+ update->version = TAG_VALUE((uint64_t)txn);
+
+ // push the new update record onto <key>'s update list
+ int64_t update_prev;
+ do {
+ update->prev = (update_rec_t *) ht_get(txn->ht, key, key_len);
+ update_prev = (int64_t)update->prev;
+ } while (ht_compare_and_set(txn->ht, key, key_len, update_prev, (int64_t)update) != update_prev);
+
+ // add <key> to the write set for commit-time validation
+ if (txn->writes_count == txn->writes_size) {
+ write_rec_t *w = nbd_malloc(sizeof(write_rec_t) * txn->writes_size * 2);
+ memcpy(w, txn->writes, txn->writes_size * sizeof(write_rec_t));
+ txn->writes_size *= 2;
+ }
+ int i = txn->writes_count++;
+ txn->writes[i].key = key;
+ txn->writes[i].rec = update;
+}
+
+#ifdef MAKE_txn_test
+#include "runtime.h"
+int main (void) {
+ nbd_init();
+ return 0;
+}
+#endif//txn_test
projects / nbds / commitdiff