#define TRUE 1
#define FALSE 0
-#define TAG (1ULL << 63)
-#define TAG_VALUE(v) ((uint64_t)(v) | TAG)
-#define IS_TAGGED(v) ((uint64_t)(v) & TAG)
-#define STRIP_TAG(v) ((uint64_t)(v) & ~TAG)
+#define TAG1 (1ULL << 63)
+#define TAG2 (1ULL << 62)
+#define TAG_VALUE(v, tag) ((uint64_t)(v) | tag)
+#define IS_TAGGED(v, tag) ((uint64_t)(v) & tag)
+#define STRIP_TAG(v, tag) ((uint64_t)(v) & ~tag)
#define DOES_NOT_EXIST 0
#define ERROR_INVALID_OPTION (-1)
OPT := -fwhole-program -combine -03 #-DNDEBUG
CFLAGS := -g -Wall -Werror -std=c99 -m64 $(OPT) #-DENABLE_TRACE
INCS := $(addprefix -I, include)
-TESTS := output/map_test1 output/map_test2 output/rcu_test output/txn_test
+TESTS := output/map_test1 output/map_test2 output/txn_test
EXES := $(TESTS)
RUNTIME_SRCS := runtime/runtime.c runtime/rcu.c runtime/lwt.c runtime/mem.c datatype/nstring.c
};
static const uint64_t COPIED_VALUE = -1;
-static const uint64_t TOMBSTONE = STRIP_TAG(-1);
+static const uint64_t TOMBSTONE = STRIP_TAG(-1, TAG1);
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;
}
// Tag the value in the old entry to indicate a copy is in progress.
- ht1_ent_val = SYNC_FETCH_AND_OR(&ht1_ent->val, TAG_VALUE(0));
+ ht1_ent_val = SYNC_FETCH_AND_OR(&ht1_ent->val, TAG_VALUE(0, TAG1));
TRACE("h2", "hti_copy_entry: tagged the value %p in old entry %p", ht1_ent_val, ht1_ent);
if (ht1_ent_val == COPIED_VALUE) {
TRACE("h1", "hti_copy_entry: entry %p already copied to table %p", ht1_ent, ht2);
void *key = (ht1->ht->key_type == NULL) ? (void *)ht1_ent_key : GET_PTR(ht1_ent_key);
// The old table's dead entries don't need to be copied to the new table, but their keys need to be freed.
- assert(COPIED_VALUE == TAG_VALUE(TOMBSTONE));
+ assert(COPIED_VALUE == TAG_VALUE(TOMBSTONE, TAG1));
if (ht1_ent_val == TOMBSTONE) {
TRACE("h1", "hti_copy_entry: entry %p old value was deleted, now freeing key %p", ht1_ent, key);
if (EXPECT_FALSE(ht1->ht->key_type != NULL)) {
}
// Copy the value to the entry in the new table.
- ht1_ent_val = STRIP_TAG(ht1_ent_val);
+ ht1_ent_val = STRIP_TAG(ht1_ent_val, TAG1);
uint64_t old_ht2_ent_val = SYNC_CAS(&ht2_ent->val, DOES_NOT_EXIST, ht1_ent_val);
// If there is a nested copy in progress, we might have installed the key into a dead entry.
TRACE("h1", "hti_cas: hti %p key %p", hti, key);
TRACE("h1", "hti_cas: value %p expect %p", new, expected);
assert(hti);
- assert(!IS_TAGGED(new));
+ assert(!IS_TAGGED(new, TAG1));
assert(key);
int is_empty;
// If the entry is in the middle of a copy, the copy must be completed first.
uint64_t ent_val = ent->val;
- if (EXPECT_FALSE(IS_TAGGED(ent_val))) {
+ if (EXPECT_FALSE(IS_TAGGED(ent_val, TAG1))) {
if (ent_val != COPIED_VALUE) {
int did_copy = hti_copy_entry(hti, ent, key_hash, ((volatile hti_t *)hti)->next);
if (did_copy) {
// If the entry is being copied, finish the copy and retry on the next table.
uint64_t ent_val = ent->val;
- if (EXPECT_FALSE(IS_TAGGED(ent_val))) {
+ if (EXPECT_FALSE(IS_TAGGED(ent_val, TAG1))) {
if (EXPECT_FALSE(ent_val != COPIED_VALUE)) {
int did_copy = hti_copy_entry(hti, ent, key_hash, ((volatile hti_t *)hti)->next);
if (did_copy) {
TRACE("h2", "ht_cas: key %p ht %p", key, ht);
TRACE("h2", "ht_cas: expected val %p new val %p", expected_val, new_val);
assert(key != DOES_NOT_EXIST);
- assert(!IS_TAGGED(new_val) && new_val != DOES_NOT_EXIST && new_val != TOMBSTONE);
+ assert(!IS_TAGGED(new_val, TAG1) && new_val != DOES_NOT_EXIST && new_val != TOMBSTONE);
hti_t *hti = ht->hti;
hti_t *hti = ht->hti;
do {
for (uint32_t i = 0; i < (1 << hti->scale); ++i) {
- assert(hti->table[i].val == COPIED_VALUE || !IS_TAGGED(hti->table[i].val));
+ assert(hti->table[i].val == COPIED_VALUE || !IS_TAGGED(hti->table[i].val, TAG1));
if (ht->key_type != NULL && hti->table[i].key != DOES_NOT_EXIST) {
nbd_free(GET_PTR(hti->table[i].key));
}
void ll_free (list_t *ll) {
node_t *item = ll->head->next;
while (item) {
- node_t *next = (node_t *)STRIP_TAG(item->next);
+ node_t *next = (node_t *)STRIP_TAG(item->next, TAG1);
nbd_free(item);
item = next;
}
uint64_t count = 0;
node_t *item = ll->head->next;
while (item) {
- if (!IS_TAGGED(item->next)) {
+ if (!IS_TAGGED(item->next, TAG1)) {
count++;
}
- item = (node_t *)STRIP_TAG(item->next);
+ item = (node_t *)STRIP_TAG(item->next, TAG1);
}
return count;
}
node_t *next = item->next;
// A tag means an item is logically removed but not physically unlinked yet.
- while (EXPECT_FALSE(IS_TAGGED(next))) {
+ while (EXPECT_FALSE(IS_TAGGED(next, TAG1))) {
// Skip over logically removed items.
if (!help_remove) {
- item = (node_t *)STRIP_TAG(item->next);
+ item = (node_t *)STRIP_TAG(item->next, TAG1);
if (EXPECT_FALSE(item == NULL))
break;
TRACE("l3", "find_pred: skipping marked item %p (next is %p)", item, next);
// Unlink logically removed items.
node_t *other;
TRACE("l3", "find_pred: unlinking marked item %p next is %p", item, next);
- if ((other = SYNC_CAS(&pred->next, item, STRIP_TAG(next))) == item) {
+ if ((other = SYNC_CAS(&pred->next, item, STRIP_TAG(next, TAG1))) == item) {
TRACE("l2", "find_pred: unlinked item %p from pred %p", item, pred);
- item = (node_t *)STRIP_TAG(next);
+ item = (node_t *)STRIP_TAG(next, TAG1);
if (EXPECT_FALSE(item == NULL))
break;
next = item->next;
} else {
TRACE("l2", "find_pred: lost a race to unlink item %p from pred %p", item, pred);
TRACE("l2", "find_pred: pred's link changed to %p", other, 0);
- if (IS_TAGGED(other))
+ if (IS_TAGGED(other, TAG1))
return find_pred(pred_ptr, item_ptr, ll, key, help_remove); // retry
item = other;
if (EXPECT_FALSE(item == NULL))
node_t *old_next = item->next;
do {
next = old_next;
- old_next = SYNC_CAS(&item->next, next, TAG_VALUE(next));
- if (IS_TAGGED(old_next)) {
+ old_next = SYNC_CAS(&item->next, next, TAG_VALUE(next, TAG1));
+ if (IS_TAGGED(old_next, TAG1)) {
TRACE("l1", "ll_remove: lost a race -- %p is already marked for removal by another thread", item, 0);
return DOES_NOT_EXIST;
}
} while (next != old_next);
TRACE("l2", "ll_remove: logically removed item %p", item, 0);
- ASSERT(IS_TAGGED(item->next));
+ ASSERT(IS_TAGGED(item->next, TAG1));
// Atomically swap out the item's value in case another thread is updating the item while we are
// removing it. This establishes which operation occurs first logically, the update or the remove.
int i = 0;
while (item) {
node_t *next = item->next;
- if (IS_TAGGED(item)) {
+ if (IS_TAGGED(item, TAG1)) {
printf("*");
}
printf("%p:%p ", item, item->key);
fflush(stdout);
- item = (node_t *)STRIP_TAG(next);
+ item = (node_t *)STRIP_TAG(next, TAG1);
if (i++ > 30) {
printf("...");
break;
void sl_free (skiplist_t *sl) {
node_t *item = sl->head->next[0];
while (item) {
- node_t *next = (node_t *)STRIP_TAG(item->next[0]);
+ node_t *next = (node_t *)STRIP_TAG(item->next[0], TAG1);
nbd_free(item);
item = next;
}
uint64_t count = 0;
node_t *item = sl->head->next[0];
while (item) {
- if (!IS_TAGGED(item->next[0])) {
+ if (!IS_TAGGED(item->next[0], TAG1)) {
count++;
}
- item = (node_t *)STRIP_TAG(item->next[0]);
+ item = (node_t *)STRIP_TAG(item->next[0], TAG1);
}
return count;
}
for (int level = start_level; level >= 0; --level) {
TRACE("s3", "find_preds: level %llu", level, 0);
item = pred->next[level];
- if (EXPECT_FALSE(IS_TAGGED(item))) {
+ if (EXPECT_FALSE(IS_TAGGED(item, TAG1))) {
TRACE("s2", "find_preds: pred %p is marked for removal (item %p); retry", pred, item);
return find_preds(preds, succs, n, sl, key, help_remove); // retry
}
node_t *next = item->next[level];
// A tag means an item is logically removed but not physically unlinked yet.
- while (EXPECT_FALSE(IS_TAGGED(next))) {
+ while (EXPECT_FALSE(IS_TAGGED(next, TAG1))) {
// Skip over logically removed items.
if (!help_remove) {
- item = (node_t *)STRIP_TAG(item->next);
+ item = (node_t *)STRIP_TAG(item->next, TAG1);
if (EXPECT_FALSE(item == NULL))
break;
TRACE("s3", "find_preds: skipping marked item %p (next is %p)", item, next);
// Unlink logically removed items.
node_t *other;
TRACE("s3", "find_preds: unlinking marked item %p; next is %p", item, next);
- if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next))) == item) {
- item = (node_t *)STRIP_TAG(next);
+ if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next, TAG1))) == item) {
+ item = (node_t *)STRIP_TAG(next, TAG1);
if (EXPECT_FALSE(item == NULL))
break;
next = item->next[level];
} else {
TRACE("s3", "find_preds: lost race to unlink item %p from pred %p", item, pred);
TRACE("s3", "find_preds: pred's link changed to %p", other, 0);
- if (IS_TAGGED(other))
+ if (IS_TAGGED(other, TAG1))
return find_preds(preds, succs, n, sl, key, help_remove); // retry
item = other;
if (EXPECT_FALSE(item == NULL))
break;
TRACE("s4", "find_preds: visiting item %p (next is %p)", item, next);
- TRACE("s4", "find_preds: key %p val %p", STRIP_TAG(item->key), item->val);
+ TRACE("s4", "find_preds: key %p val %p", STRIP_TAG(item->key, TAG1), item->val);
if (EXPECT_TRUE(sl->key_type == NULL)) {
d = (uint64_t)item->key - (uint64_t)key;
node_t *item = sl->head->next[0];
while (item != NULL) {
node_t *next = item->next[0];
- if (!IS_TAGGED(next))
+ if (!IS_TAGGED(next, TAG1))
return item->key;
- item = (node_t *)STRIP_TAG(next);
+ item = (node_t *)STRIP_TAG(next, TAG1);
}
return DOES_NOT_EXIST;
}
do {
// There in no need to continue linking in the item if another thread removed it.
node_t *old_next = ((volatile node_t *)new_item)->next[level];
- if (IS_TAGGED(old_next))
+ if (IS_TAGGED(old_next, TAG1))
return DOES_NOT_EXIST; // success
// Use a CAS so we do not inadvertantly stomp on a mark another thread placed on the item.
node_t *old_next = item->next[level];
do {
next = old_next;
- old_next = SYNC_CAS(&item->next[level], next, TAG_VALUE(next));
- if (IS_TAGGED(old_next)) {
+ old_next = SYNC_CAS(&item->next[level], next, TAG_VALUE(next, TAG1));
+ if (IS_TAGGED(old_next, TAG1)) {
TRACE("s2", "sl_remove: %p is already marked for removal by another thread at level %llu", item, level);
break;
}
} while (next != old_next);
node_t *pred = preds[level];
- TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next));
+ TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next, TAG1));
node_t *other = NULL;
- if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next))) != item) {
+ if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next, TAG1))) != item) {
TRACE("s1", "sl_remove: unlink failed; pred's link changed from %p to %p", item, other);
// If our former predecessor now points past us we know another thread unlinked us. Otherwise, we need
// to search for a new set of preds.
continue; // <pred> points past <item> to the end of the list; go on to the next level.
int d = -1;
- if (!IS_TAGGED(other)) {
+ if (!IS_TAGGED(other, TAG1)) {
if (EXPECT_TRUE(sl->key_type == NULL)) {
d = (uint64_t)item->key - (uint64_t)other->key;
} else {
node_t *old_next = item->next[0];
do {
next = old_next;
- old_next = SYNC_CAS(&item->next[0], next, TAG_VALUE(next));
- if (IS_TAGGED(old_next)) {
+ old_next = SYNC_CAS(&item->next[0], next, TAG_VALUE(next, TAG1));
+ if (IS_TAGGED(old_next, TAG1)) {
TRACE("s2", "sl_remove: %p is already marked for removal by another thread at level 0", item, 0);
return DOES_NOT_EXIST;
}
TRACE("s2", "sl_remove: replaced item %p's value with DOES_NOT_EXIT", item, 0);
node_t *pred = preds[0];
- TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next));
- if (SYNC_CAS(&pred->next[0], item, STRIP_TAG(next))) {
+ TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next, TAG1));
+ if (SYNC_CAS(&pred->next[0], item, STRIP_TAG(next, TAG1))) {
TRACE("s2", "sl_remove: unlinked item %p from the skiplist at level 0", item, 0);
// The thread that completes the unlink should free the memory.
if (sl->key_type != NULL) {
int i = 0;
while (item) {
node_t *next = item->next[level];
- printf("%s%p ", IS_TAGGED(next) ? "*" : "", item);
- item = (node_t *)STRIP_TAG(next);
+ printf("%s%p ", IS_TAGGED(next, TAG1) ? "*" : "", item);
+ item = (node_t *)STRIP_TAG(next, TAG1);
if (i++ > 30) {
printf("...");
break;
node_t *item = sl->head;
int i = 0;
while (item) {
- int is_marked = IS_TAGGED(item->next[0]);
+ int is_marked = IS_TAGGED(item->next[0], TAG1);
printf("%s%p:%p ", is_marked ? "*" : "", item, item->key);
if (item != sl->head) {
printf("[%d]", item->top_level);
printf("[HEAD]");
}
for (int level = 1; level <= item->top_level; ++level) {
- node_t *next = (node_t *)STRIP_TAG(item->next[level]);
- is_marked = IS_TAGGED(item->next[0]);
+ node_t *next = (node_t *)STRIP_TAG(item->next[level], TAG1);
+ is_marked = IS_TAGGED(item->next[0], TAG1);
printf(" %p%s", next, is_marked ? "*" : "");
if (item == sl->head && item->next[level] == NULL)
break;
}
printf("\n");
fflush(stdout);
- item = (node_t *)STRIP_TAG(item->next[0]);
+ item = (node_t *)STRIP_TAG(item->next[0], TAG1);
if (i++ > 30) {
printf("...\n");
break;
#include "skiplist.h"
#define UNDETERMINED_VERSION 0
-#define ABORTED_VERSION TAG_VALUE(0)
+#define ABORTED_VERSION TAG_VALUE(0, TAG1)
#define INITIAL_WRITES_SIZE 4
-typedef enum { UPDATE_TYPE_PUT, UPDATE_TYPE_DELETE } update_type_t;
-
-typedef struct update_rec update_rec_t;
+typedef struct update_rec update_t;
struct update_rec {
- update_type_t type;
- uint64_t value;
+ update_t *next; // an earlier update
uint64_t version;
- update_rec_t *next; // an earlier update
+ uint64_t value;
};
typedef struct write_rec {
void *key;
- update_rec_t *rec;
+ update_t *rec;
} write_rec_t;
struct txn {
//
static txn_state_e tm_validate_key (txn_t *txn, void *key) {
- update_rec_t *update = (update_rec_t *) map_get(txn->map, key);
+ update_t *update = (update_t *) map_get(txn->map, key);
for (; update != NULL; update = update->next) {
- // If the update's version is not tagged it means the update is committed.
+ // If the update or its version is not tagged it means the update is committed.
//
// We can stop at the first committed record we find that is at least as old as our read version. All
// the other committed records following it will be older. And all the uncommitted records following it
// will eventually conflict with it and abort.
- if (!IS_TAGGED(update->version))
+ if (!IS_TAGGED(update, TAG2))
+ return TXN_VALIDATED;
+ update = (update_t *)STRIP_TAG(update, TAG2);
+ if (!IS_TAGGED(update->version, TAG1))
return (update->version <= txn->rv) ? TXN_VALIDATED : TXN_ABORTED;
// If the update's version is tagged then either the update was aborted or the the version number is
continue;
// The update's transaction is still in progress. Access its txn_t.
- txn_t *writer = (txn_t *)STRIP_TAG(update->version);
+ txn_t *writer = (txn_t *)STRIP_TAG(update->version, TAG1);
if (writer == txn)
continue; // Skip our own updates.
txn_state_e writer_state = writer->state;
- // Any running transaction will only be able to aquire a wv greater than ours. A transaction changes its
+ // Any running transaction will only be able to acquire a wv greater than ours. A transaction changes its
// state to validating before aquiring a wv. We can ignore an unvalidated transaction if its version is
// greater than ours. See next comment below for why.
if (writer_state == TXN_RUNNING)
return txn->state;
}
-static 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));
+static update_t *alloc_update_rec (void) {
+ update_t *u = (update_t *)nbd_malloc(sizeof(update_t));
+ memset(u, 0, sizeof(update_t));
return u;
}
txn->writes_size = INITIAL_WRITES_SIZE;
}
- // aquire the read version for txn. must be careful to avoid a race
+ // acquire the read version for txn. must be careful to avoid a race
do {
txn->rv = version_;
int i;
for (i = 0; i < txn->writes_count; ++i) {
- update_rec_t *update = (update_rec_t *)txn->writes[i].rec;
+ update_t *update = (update_t *)txn->writes[i].rec;
update->version = ABORTED_VERSION;
}
uint64_t wv = (txn->state == TXN_ABORTED) ? ABORTED_VERSION : txn->wv;
int i;
for (i = 0; i < txn->writes_count; ++i) {
- update_rec_t *update = (update_rec_t *)txn->writes[i].rec;
+ update_t *update = (update_t *)txn->writes[i].rec;
update->version = wv;
}
// Get most recent committed version prior to our read version.
uint64_t tm_get (txn_t *txn, void *key) {
- // Iterate through update records associated with <key> to find the latest committed version prior to our
- // read version.
- update_rec_t *update = (update_rec_t *) map_get(txn->map, key);
- for (; update != NULL; update = update->next) {
+ update_t *newest_update = (update_t *) map_get(txn->map, key);
+ if (!IS_TAGGED(newest_update, TAG2))
+ return (uint64_t)newest_update;
+
+ // Iterate through the update records to find the latest committed version prior to our read version.
+ update_t *update;
+ for (update = newest_update; ; update = update->next) {
+
+ if (!IS_TAGGED(update, TAG2))
+ return (uint64_t)update;
+
+ update = (update_t *)STRIP_TAG(update, TAG2);
+ assert(update != NULL);
// If the update's version is not tagged it means the update is committed.
- if (!IS_TAGGED(update->version)) {
+ if (!IS_TAGGED(update->version, TAG1)) {
if (update->version <= txn->rv)
break; // success
continue;
continue;
// The update's transaction is still in progress. Access its txn_t.
- txn_t *writer = (txn_t *)STRIP_TAG(update->version);
+ txn_t *writer = (txn_t *)STRIP_TAG(update->version, TAG1);
if (writer == txn) // found our own update
break; // success
break; // success
}
- if (EXPECT_FALSE(update == NULL))
- return DOES_NOT_EXIST;
+ uint64_t value = update->value;
// collect some garbage
- update_rec_t *next = update->next;
- if (next != NULL) {
- uint64_t min_active_version = (uint64_t)sl_min_key(active_);
- if (next->version < min_active_version) {
- next = SYNC_SWAP(&update->next, NULL);
- while (next != NULL) {
+ update_t *last = update;
+ update_t *next = update->next;
+ uint64_t min_active = 0;
+ if (IS_TAGGED(next, TAG2)) {
+ next = (update_t *)STRIP_TAG(next, TAG2);
+ min_active = (uint64_t)sl_min_key(active_);
+ if (next->version < min_active) {
+
+ // Skip over aborted versions to verify the chain of updates is old enough for collection
+ update_t *temp = next;
+ while (temp->version == ABORTED_VERSION) {
+ assert(!IS_TAGGED(temp->version, TAG1));
+ update_t *temp = next->next;
+ if (!IS_TAGGED(temp, TAG2))
+ break;
+ temp = (update_t *)STRIP_TAG(temp, TAG2);
+ if (temp->version >= min_active)
+ return value;
+ temp = temp->next;
+ }
+
+ // collect <next> and all the update records following it
+ do {
+ next = SYNC_SWAP(&update->next, NULL);
+
+ // if we find ourself in a race just back off and let the other thread take care of it
+ if (next == NULL)
+ return value;
+
update = next;
- next = NULL;
- if (update->next != NULL) {
- next = SYNC_SWAP(&update->next, NULL);
- }
+ next = next->next;
nbd_free(update);
- }
+ } while (IS_TAGGED(next, TAG2));
}
}
+
+ // If there is one item left and it is visible by all active transactions we can merge it into the map itself.
+ // There is no need for an update record.
+ if (next == NULL && last == (update_t *)STRIP_TAG(newest_update, TAG2)) {
+ if (min_active == UNDETERMINED_VERSION) {
+ min_active = (uint64_t)sl_min_key(active_);
+ }
+ if (last->version <= min_active) {
+ if (map_cas(txn->map, key, TAG_VALUE(last, TAG2), value) == TAG_VALUE(last, TAG2)) {
+ nbd_defer_free(last);
+ }
+ }
+ }
- return update->value;
+ return value;
}
void tm_set (txn_t *txn, void *key, uint64_t value) {
// create a new update record
- update_rec_t *update = alloc_update_rec();
- update->type = UPDATE_TYPE_PUT;
+ update_t *update = alloc_update_rec();
update->value = value;
- update->version = TAG_VALUE((uint64_t)txn);
+ update->version = TAG_VALUE(txn, TAG1);
// push the new update record onto <key>'s update list
- uint64_t update_prev;
+ uint64_t old_update;
do {
- update->next = (update_rec_t *) map_get(txn->map, key);
- update_prev = (uint64_t)update->next;
- } while (map_cas(txn->map, key, update_prev, (uint64_t)update) != update_prev);
+ old_update = map_get(txn->map, key);
+ update->next = (update_t *)old_update;
+ } while (map_cas(txn->map, key, old_update, TAG_VALUE(update, TAG2)) != old_update);
// 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;
+ nbd_free(txn->writes);
+ txn->writes = w;
}
int i = txn->writes_count++;
txn->writes[i].key = key;