+/* ============ Virtual Memory - Blocking clients on missing keys =========== */
+
+/* This function makes the clinet 'c' waiting for the key 'key' to be loaded.
+ * If there is not already a job loading the key, it is craeted.
+ * The key is added to the io_keys list in the client structure, and also
+ * in the hash table mapping swapped keys to waiting clients, that is,
+ * server.io_waited_keys. */
+static int waitForSwappedKey(redisClient *c, robj *key) {
+ struct dictEntry *de;
+ robj *o;
+ list *l;
+
+ /* If the key does not exist or is already in RAM we don't need to
+ * block the client at all. */
+ de = dictFind(c->db->dict,key);
+ if (de == NULL) return 0;
+ o = dictGetEntryKey(de);
+ if (o->storage == REDIS_VM_MEMORY) {
+ return 0;
+ } else if (o->storage == REDIS_VM_SWAPPING) {
+ /* We were swapping the key, undo it! */
+ vmCancelThreadedIOJob(o);
+ return 0;
+ }
+
+ /* OK: the key is either swapped, or being loaded just now. */
+
+ /* Add the key to the list of keys this client is waiting for.
+ * This maps clients to keys they are waiting for. */
+ listAddNodeTail(c->io_keys,key);
+ incrRefCount(key);
+
+ /* Add the client to the swapped keys => clients waiting map. */
+ de = dictFind(c->db->io_keys,key);
+ if (de == NULL) {
+ int retval;
+
+ /* For every key we take a list of clients blocked for it */
+ l = listCreate();
+ retval = dictAdd(c->db->io_keys,key,l);
+ incrRefCount(key);
+ assert(retval == DICT_OK);
+ } else {
+ l = dictGetEntryVal(de);
+ }
+ listAddNodeTail(l,c);
+
+ /* Are we already loading the key from disk? If not create a job */
+ if (o->storage == REDIS_VM_SWAPPED) {
+ iojob *j;
+
+ o->storage = REDIS_VM_LOADING;
+ j = zmalloc(sizeof(*j));
+ j->type = REDIS_IOJOB_LOAD;
+ j->db = c->db;
+ j->key = dupStringObject(key);
+ j->key->vtype = o->vtype;
+ j->page = o->vm.page;
+ j->val = NULL;
+ j->canceled = 0;
+ j->thread = (pthread_t) -1;
+ lockThreadedIO();
+ queueIOJob(j);
+ unlockThreadedIO();
+ }
+ return 1;
+}
+
+/* Is this client attempting to run a command against swapped keys?
+ * If so, block it ASAP, load the keys in background, then resume it.
+ *
+ * The important idea about this function is that it can fail! If keys will
+ * still be swapped when the client is resumed, this key lookups will
+ * just block loading keys from disk. In practical terms this should only
+ * happen with SORT BY command or if there is a bug in this function.
+ *
+ * Return 1 if the client is marked as blocked, 0 if the client can
+ * continue as the keys it is going to access appear to be in memory. */
+static int blockClientOnSwappedKeys(struct redisCommand *cmd, redisClient *c) {
+ if (cmd->proc == getCommand) {
+ waitForSwappedKey(c,c->argv[1]);
+ }
+ /* If the client was blocked for at least one key, mark it as blocked. */
+ if (listLength(c->io_keys)) {
+ c->flags |= REDIS_IO_WAIT;
+ aeDeleteFileEvent(server.el,c->fd,AE_READABLE);
+ server.vm_blocked_clients++;
+ return 1;
+ } else {
+ return 0;
+ }
+}
+
+/* Remove the 'key' from the list of blocked keys for a given client.
+ *
+ * The function returns 1 when there are no longer blocking keys after
+ * the current one was removed (and the client can be unblocked). */
+static int dontWaitForSwappedKey(redisClient *c, robj *key) {
+ list *l;
+ listNode *ln;
+ listIter li;
+ struct dictEntry *de;
+
+ /* Remove the key from the list of keys this client is waiting for. */
+ listRewind(c->io_keys,&li);
+ while ((ln = listNext(&li)) != NULL) {
+ if (compareStringObjects(ln->value,key) == 0) {
+ listDelNode(c->io_keys,ln);
+ break;
+ }
+ }
+ assert(ln != NULL);
+
+ /* Remove the client form the key => waiting clients map. */
+ de = dictFind(c->db->io_keys,key);
+ assert(de != NULL);
+ l = dictGetEntryVal(de);
+ ln = listSearchKey(l,c);
+ assert(ln != NULL);
+ listDelNode(l,ln);
+ if (listLength(l) == 0)
+ dictDelete(c->db->io_keys,key);
+
+ return listLength(c->io_keys) == 0;
+}
+
+static void handleClientsBlockedOnSwappedKey(redisDb *db, robj *key) {
+ struct dictEntry *de;
+ list *l;
+ listNode *ln;
+ int len;
+
+ de = dictFind(db->io_keys,key);
+ if (!de) return;
+
+ l = dictGetEntryVal(de);
+ len = listLength(l);
+ /* Note: we can't use something like while(listLength(l)) as the list
+ * can be freed by the calling function when we remove the last element. */
+ while (len--) {
+ ln = listFirst(l);
+ redisClient *c = ln->value;
+
+ if (dontWaitForSwappedKey(c,key)) {
+ /* Put the client in the list of clients ready to go as we
+ * loaded all the keys about it. */
+ listAddNodeTail(server.io_ready_clients,c);
+ }
+ }
+}
+
projects / redis.git / blobdiff