#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;
projects / nbds / blobdiff