src/t_list.c

   1 #include "redis.h"
   2
   3 /*-----------------------------------------------------------------------------
   4  * List API
   5  *----------------------------------------------------------------------------*/
   6
   7 /* Check the argument length to see if it requires us to convert the ziplist
   8  * to a real list. Only check raw-encoded objects because integer encoded
   9  * objects are never too long. */
  10 void listTypeTryConversion(robj *subject, robj *value) {
  11     if (subject->encoding != REDIS_ENCODING_ZIPLIST) return;
  12     if (value->encoding == REDIS_ENCODING_RAW &&
  13         sdslen(value->ptr) > server.list_max_ziplist_value)
  14             listTypeConvert(subject,REDIS_ENCODING_LINKEDLIST);
  15 }
  16
  17 void listTypePush(robj *subject, robj *value, int where) {
  18     /* Check if we need to convert the ziplist */
  19     listTypeTryConversion(subject,value);
  20     if (subject->encoding == REDIS_ENCODING_ZIPLIST &&
  21         ziplistLen(subject->ptr) >= server.list_max_ziplist_entries)
  22             listTypeConvert(subject,REDIS_ENCODING_LINKEDLIST);
  23
  24     if (subject->encoding == REDIS_ENCODING_ZIPLIST) {
  25         int pos = (where == REDIS_HEAD) ? ZIPLIST_HEAD : ZIPLIST_TAIL;
  26         value = getDecodedObject(value);
  27         subject->ptr = ziplistPush(subject->ptr,value->ptr,sdslen(value->ptr),pos);
  28         decrRefCount(value);
  29     } else if (subject->encoding == REDIS_ENCODING_LINKEDLIST) {
  30         if (where == REDIS_HEAD) {
  31             listAddNodeHead(subject->ptr,value);
  32         } else {
  33             listAddNodeTail(subject->ptr,value);
  34         }
  35         incrRefCount(value);
  36     } else {
  37         redisPanic("Unknown list encoding");
  38     }
  39 }
  40
  41 robj *listTypePop(robj *subject, int where) {
  42     robj *value = NULL;
  43     if (subject->encoding == REDIS_ENCODING_ZIPLIST) {
  44         unsigned char *p;
  45         unsigned char *vstr;
  46         unsigned int vlen;
  47         long long vlong;
  48         int pos = (where == REDIS_HEAD) ? 0 : -1;
  49         p = ziplistIndex(subject->ptr,pos);
  50         if (ziplistGet(p,&vstr,&vlen,&vlong)) {
  51             if (vstr) {
  52                 value = createStringObject((char*)vstr,vlen);
  53             } else {
  54                 value = createStringObjectFromLongLong(vlong);
  55             }
  56             /* We only need to delete an element when it exists */
  57             subject->ptr = ziplistDelete(subject->ptr,&p);
  58         }
  59     } else if (subject->encoding == REDIS_ENCODING_LINKEDLIST) {
  60         list *list = subject->ptr;
  61         listNode *ln;
  62         if (where == REDIS_HEAD) {
  63             ln = listFirst(list);
  64         } else {
  65             ln = listLast(list);
  66         }
  67         if (ln != NULL) {
  68             value = listNodeValue(ln);
  69             incrRefCount(value);
  70             listDelNode(list,ln);
  71         }
  72     } else {
  73         redisPanic("Unknown list encoding");
  74     }
  75     return value;
  76 }
  77
  78 unsigned long listTypeLength(robj *subject) {
  79     if (subject->encoding == REDIS_ENCODING_ZIPLIST) {
  80         return ziplistLen(subject->ptr);
  81     } else if (subject->encoding == REDIS_ENCODING_LINKEDLIST) {
  82         return listLength((list*)subject->ptr);
  83     } else {
  84         redisPanic("Unknown list encoding");
  85     }
  86 }
  87
  88 /* Initialize an iterator at the specified index. */
  89 listTypeIterator *listTypeInitIterator(robj *subject, int index, unsigned char direction) {
  90     listTypeIterator *li = zmalloc(sizeof(listTypeIterator));
  91     li->subject = subject;
  92     li->encoding = subject->encoding;
  93     li->direction = direction;
  94     if (li->encoding == REDIS_ENCODING_ZIPLIST) {
  95         li->zi = ziplistIndex(subject->ptr,index);
  96     } else if (li->encoding == REDIS_ENCODING_LINKEDLIST) {
  97         li->ln = listIndex(subject->ptr,index);
  98     } else {
  99         redisPanic("Unknown list encoding");
 100     }
 101     return li;
 102 }
 103
 104 /* Clean up the iterator. */
 105 void listTypeReleaseIterator(listTypeIterator *li) {
 106     zfree(li);
 107 }
 108
 109 /* Stores pointer to current the entry in the provided entry structure
 110  * and advances the position of the iterator. Returns 1 when the current
 111  * entry is in fact an entry, 0 otherwise. */
 112 int listTypeNext(listTypeIterator *li, listTypeEntry *entry) {
 113     /* Protect from converting when iterating */
 114     redisAssert(li->subject->encoding == li->encoding);
 115
 116     entry->li = li;
 117     if (li->encoding == REDIS_ENCODING_ZIPLIST) {
 118         entry->zi = li->zi;
 119         if (entry->zi != NULL) {
 120             if (li->direction == REDIS_TAIL)
 121                 li->zi = ziplistNext(li->subject->ptr,li->zi);
 122             else
 123                 li->zi = ziplistPrev(li->subject->ptr,li->zi);
 124             return 1;
 125         }
 126     } else if (li->encoding == REDIS_ENCODING_LINKEDLIST) {
 127         entry->ln = li->ln;
 128         if (entry->ln != NULL) {
 129             if (li->direction == REDIS_TAIL)
 130                 li->ln = li->ln->next;
 131             else
 132                 li->ln = li->ln->prev;
 133             return 1;
 134         }
 135     } else {
 136         redisPanic("Unknown list encoding");
 137     }
 138     return 0;
 139 }
 140
 141 /* Return entry or NULL at the current position of the iterator. */
 142 robj *listTypeGet(listTypeEntry *entry) {
 143     listTypeIterator *li = entry->li;
 144     robj *value = NULL;
 145     if (li->encoding == REDIS_ENCODING_ZIPLIST) {
 146         unsigned char *vstr;
 147         unsigned int vlen;
 148         long long vlong;
 149         redisAssert(entry->zi != NULL);
 150         if (ziplistGet(entry->zi,&vstr,&vlen,&vlong)) {
 151             if (vstr) {
 152                 value = createStringObject((char*)vstr,vlen);
 153             } else {
 154                 value = createStringObjectFromLongLong(vlong);
 155             }
 156         }
 157     } else if (li->encoding == REDIS_ENCODING_LINKEDLIST) {
 158         redisAssert(entry->ln != NULL);
 159         value = listNodeValue(entry->ln);
 160         incrRefCount(value);
 161     } else {
 162         redisPanic("Unknown list encoding");
 163     }
 164     return value;
 165 }
 166
 167 void listTypeInsert(listTypeEntry *entry, robj *value, int where) {
 168     robj *subject = entry->li->subject;
 169     if (entry->li->encoding == REDIS_ENCODING_ZIPLIST) {
 170         value = getDecodedObject(value);
 171         if (where == REDIS_TAIL) {
 172             unsigned char *next = ziplistNext(subject->ptr,entry->zi);
 173
 174             /* When we insert after the current element, but the current element
 175              * is the tail of the list, we need to do a push. */
 176             if (next == NULL) {
 177                 subject->ptr = ziplistPush(subject->ptr,value->ptr,sdslen(value->ptr),REDIS_TAIL);
 178             } else {
 179                 subject->ptr = ziplistInsert(subject->ptr,next,value->ptr,sdslen(value->ptr));
 180             }
 181         } else {
 182             subject->ptr = ziplistInsert(subject->ptr,entry->zi,value->ptr,sdslen(value->ptr));
 183         }
 184         decrRefCount(value);
 185     } else if (entry->li->encoding == REDIS_ENCODING_LINKEDLIST) {
 186         if (where == REDIS_TAIL) {
 187             listInsertNode(subject->ptr,entry->ln,value,AL_START_TAIL);
 188         } else {
 189             listInsertNode(subject->ptr,entry->ln,value,AL_START_HEAD);
 190         }
 191         incrRefCount(value);
 192     } else {
 193         redisPanic("Unknown list encoding");
 194     }
 195 }
 196
 197 /* Compare the given object with the entry at the current position. */
 198 int listTypeEqual(listTypeEntry *entry, robj *o) {
 199     listTypeIterator *li = entry->li;
 200     if (li->encoding == REDIS_ENCODING_ZIPLIST) {
 201         redisAssert(o->encoding == REDIS_ENCODING_RAW);
 202         return ziplistCompare(entry->zi,o->ptr,sdslen(o->ptr));
 203     } else if (li->encoding == REDIS_ENCODING_LINKEDLIST) {
 204         return equalStringObjects(o,listNodeValue(entry->ln));
 205     } else {
 206         redisPanic("Unknown list encoding");
 207     }
 208 }
 209
 210 /* Delete the element pointed to. */
 211 void listTypeDelete(listTypeEntry *entry) {
 212     listTypeIterator *li = entry->li;
 213     if (li->encoding == REDIS_ENCODING_ZIPLIST) {
 214         unsigned char *p = entry->zi;
 215         li->subject->ptr = ziplistDelete(li->subject->ptr,&p);
 216
 217         /* Update position of the iterator depending on the direction */
 218         if (li->direction == REDIS_TAIL)
 219             li->zi = p;
 220         else
 221             li->zi = ziplistPrev(li->subject->ptr,p);
 222     } else if (entry->li->encoding == REDIS_ENCODING_LINKEDLIST) {
 223         listNode *next;
 224         if (li->direction == REDIS_TAIL)
 225             next = entry->ln->next;
 226         else
 227             next = entry->ln->prev;
 228         listDelNode(li->subject->ptr,entry->ln);
 229         li->ln = next;
 230     } else {
 231         redisPanic("Unknown list encoding");
 232     }
 233 }
 234
 235 void listTypeConvert(robj *subject, int enc) {
 236     listTypeIterator *li;
 237     listTypeEntry entry;
 238     redisAssert(subject->type == REDIS_LIST);
 239
 240     if (enc == REDIS_ENCODING_LINKEDLIST) {
 241         list *l = listCreate();
 242         listSetFreeMethod(l,decrRefCount);
 243
 244         /* listTypeGet returns a robj with incremented refcount */
 245         li = listTypeInitIterator(subject,0,REDIS_TAIL);
 246         while (listTypeNext(li,&entry)) listAddNodeTail(l,listTypeGet(&entry));
 247         listTypeReleaseIterator(li);
 248
 249         subject->encoding = REDIS_ENCODING_LINKEDLIST;
 250         zfree(subject->ptr);
 251         subject->ptr = l;
 252     } else {
 253         redisPanic("Unsupported list conversion");
 254     }
 255 }
 256
 257 /*-----------------------------------------------------------------------------
 258  * List Commands
 259  *----------------------------------------------------------------------------*/
 260
 261 void pushGenericCommand(redisClient *c, int where) {
 262     robj *lobj = lookupKeyWrite(c->db,c->argv[1]);
 263     if (lobj == NULL) {
 264         if (handleClientsWaitingListPush(c,c->argv[1],c->argv[2])) {
 265             addReply(c,shared.cone);
 266             return;
 267         }
 268         lobj = createZiplistObject();
 269         dbAdd(c->db,c->argv[1],lobj);
 270     } else {
 271         if (lobj->type != REDIS_LIST) {
 272             addReply(c,shared.wrongtypeerr);
 273             return;
 274         }
 275         if (handleClientsWaitingListPush(c,c->argv[1],c->argv[2])) {
 276             touchWatchedKey(c->db,c->argv[1]);
 277             addReply(c,shared.cone);
 278             return;
 279         }
 280     }
 281     listTypePush(lobj,c->argv[2],where);
 282     addReplyLongLong(c,listTypeLength(lobj));
 283     touchWatchedKey(c->db,c->argv[1]);
 284     server.dirty++;
 285 }
 286
 287 void lpushCommand(redisClient *c) {
 288     pushGenericCommand(c,REDIS_HEAD);
 289 }
 290
 291 void rpushCommand(redisClient *c) {
 292     pushGenericCommand(c,REDIS_TAIL);
 293 }
 294
 295 void pushxGenericCommand(redisClient *c, robj *refval, robj *val, int where) {
 296     robj *subject;
 297     listTypeIterator *iter;
 298     listTypeEntry entry;
 299     int inserted = 0;
 300
 301     if ((subject = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
 302         checkType(c,subject,REDIS_LIST)) return;
 303
 304     if (refval != NULL) {
 305         /* Note: we expect refval to be string-encoded because it is *not* the
 306          * last argument of the multi-bulk LINSERT. */
 307         redisAssert(refval->encoding == REDIS_ENCODING_RAW);
 308
 309         /* We're not sure if this value can be inserted yet, but we cannot
 310          * convert the list inside the iterator. We don't want to loop over
 311          * the list twice (once to see if the value can be inserted and once
 312          * to do the actual insert), so we assume this value can be inserted
 313          * and convert the ziplist to a regular list if necessary. */
 314         listTypeTryConversion(subject,val);
 315
 316         /* Seek refval from head to tail */
 317         iter = listTypeInitIterator(subject,0,REDIS_TAIL);
 318         while (listTypeNext(iter,&entry)) {
 319             if (listTypeEqual(&entry,refval)) {
 320                 listTypeInsert(&entry,val,where);
 321                 inserted = 1;
 322                 break;
 323             }
 324         }
 325         listTypeReleaseIterator(iter);
 326
 327         if (inserted) {
 328             /* Check if the length exceeds the ziplist length threshold. */
 329             if (subject->encoding == REDIS_ENCODING_ZIPLIST &&
 330                 ziplistLen(subject->ptr) > server.list_max_ziplist_entries)
 331                     listTypeConvert(subject,REDIS_ENCODING_LINKEDLIST);
 332             touchWatchedKey(c->db,c->argv[1]);
 333             server.dirty++;
 334         } else {
 335             /* Notify client of a failed insert */
 336             addReply(c,shared.cnegone);
 337             return;
 338         }
 339     } else {
 340         listTypePush(subject,val,where);
 341         touchWatchedKey(c->db,c->argv[1]);
 342         server.dirty++;
 343     }
 344
 345     addReplyUlong(c,listTypeLength(subject));
 346 }
 347
 348 void lpushxCommand(redisClient *c) {
 349     pushxGenericCommand(c,NULL,c->argv[2],REDIS_HEAD);
 350 }
 351
 352 void rpushxCommand(redisClient *c) {
 353     pushxGenericCommand(c,NULL,c->argv[2],REDIS_TAIL);
 354 }
 355
 356 void linsertCommand(redisClient *c) {
 357     if (strcasecmp(c->argv[2]->ptr,"after") == 0) {
 358         pushxGenericCommand(c,c->argv[3],c->argv[4],REDIS_TAIL);
 359     } else if (strcasecmp(c->argv[2]->ptr,"before") == 0) {
 360         pushxGenericCommand(c,c->argv[3],c->argv[4],REDIS_HEAD);
 361     } else {
 362         addReply(c,shared.syntaxerr);
 363     }
 364 }
 365
 366 void llenCommand(redisClient *c) {
 367     robj *o = lookupKeyReadOrReply(c,c->argv[1],shared.czero);
 368     if (o == NULL || checkType(c,o,REDIS_LIST)) return;
 369     addReplyUlong(c,listTypeLength(o));
 370 }
 371
 372 void lindexCommand(redisClient *c) {
 373     robj *o = lookupKeyReadOrReply(c,c->argv[1],shared.nullbulk);
 374     if (o == NULL || checkType(c,o,REDIS_LIST)) return;
 375     int index = atoi(c->argv[2]->ptr);
 376     robj *value = NULL;
 377
 378     if (o->encoding == REDIS_ENCODING_ZIPLIST) {
 379         unsigned char *p;
 380         unsigned char *vstr;
 381         unsigned int vlen;
 382         long long vlong;
 383         p = ziplistIndex(o->ptr,index);
 384         if (ziplistGet(p,&vstr,&vlen,&vlong)) {
 385             if (vstr) {
 386                 value = createStringObject((char*)vstr,vlen);
 387             } else {
 388                 value = createStringObjectFromLongLong(vlong);
 389             }
 390             addReplyBulk(c,value);
 391             decrRefCount(value);
 392         } else {
 393             addReply(c,shared.nullbulk);
 394         }
 395     } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
 396         listNode *ln = listIndex(o->ptr,index);
 397         if (ln != NULL) {
 398             value = listNodeValue(ln);
 399             addReplyBulk(c,value);
 400         } else {
 401             addReply(c,shared.nullbulk);
 402         }
 403     } else {
 404         redisPanic("Unknown list encoding");
 405     }
 406 }
 407
 408 void lsetCommand(redisClient *c) {
 409     robj *o = lookupKeyWriteOrReply(c,c->argv[1],shared.nokeyerr);
 410     if (o == NULL || checkType(c,o,REDIS_LIST)) return;
 411     int index = atoi(c->argv[2]->ptr);
 412     robj *value = c->argv[3];
 413
 414     listTypeTryConversion(o,value);
 415     if (o->encoding == REDIS_ENCODING_ZIPLIST) {
 416         unsigned char *p, *zl = o->ptr;
 417         p = ziplistIndex(zl,index);
 418         if (p == NULL) {
 419             addReply(c,shared.outofrangeerr);
 420         } else {
 421             o->ptr = ziplistDelete(o->ptr,&p);
 422             value = getDecodedObject(value);
 423             o->ptr = ziplistInsert(o->ptr,p,value->ptr,sdslen(value->ptr));
 424             decrRefCount(value);
 425             addReply(c,shared.ok);
 426             touchWatchedKey(c->db,c->argv[1]);
 427             server.dirty++;
 428         }
 429     } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
 430         listNode *ln = listIndex(o->ptr,index);
 431         if (ln == NULL) {
 432             addReply(c,shared.outofrangeerr);
 433         } else {
 434             decrRefCount((robj*)listNodeValue(ln));
 435             listNodeValue(ln) = value;
 436             incrRefCount(value);
 437             addReply(c,shared.ok);
 438             touchWatchedKey(c->db,c->argv[1]);
 439             server.dirty++;
 440         }
 441     } else {
 442         redisPanic("Unknown list encoding");
 443     }
 444 }
 445
 446 void popGenericCommand(redisClient *c, int where) {
 447     robj *o = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk);
 448     if (o == NULL || checkType(c,o,REDIS_LIST)) return;
 449
 450     robj *value = listTypePop(o,where);
 451     if (value == NULL) {
 452         addReply(c,shared.nullbulk);
 453     } else {
 454         addReplyBulk(c,value);
 455         decrRefCount(value);
 456         if (listTypeLength(o) == 0) dbDelete(c->db,c->argv[1]);
 457         touchWatchedKey(c->db,c->argv[1]);
 458         server.dirty++;
 459     }
 460 }
 461
 462 void lpopCommand(redisClient *c) {
 463     popGenericCommand(c,REDIS_HEAD);
 464 }
 465
 466 void rpopCommand(redisClient *c) {
 467     popGenericCommand(c,REDIS_TAIL);
 468 }
 469
 470 void lrangeCommand(redisClient *c) {
 471     robj *o, *value;
 472     int start = atoi(c->argv[2]->ptr);
 473     int end = atoi(c->argv[3]->ptr);
 474     int llen;
 475     int rangelen, j;
 476     listTypeEntry entry;
 477
 478     if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk)) == NULL
 479          || checkType(c,o,REDIS_LIST)) return;
 480     llen = listTypeLength(o);
 481
 482     /* convert negative indexes */
 483     if (start < 0) start = llen+start;
 484     if (end < 0) end = llen+end;
 485     if (start < 0) start = 0;
 486
 487     /* Invariant: start >= 0, so this test will be true when end < 0.
 488      * The range is empty when start > end or start >= length. */
 489     if (start > end || start >= llen) {
 490         addReply(c,shared.emptymultibulk);
 491         return;
 492     }
 493     if (end >= llen) end = llen-1;
 494     rangelen = (end-start)+1;
 495
 496     /* Return the result in form of a multi-bulk reply */
 497     addReplySds(c,sdscatprintf(sdsempty(),"*%d\r\n",rangelen));
 498     listTypeIterator *li = listTypeInitIterator(o,start,REDIS_TAIL);
 499     for (j = 0; j < rangelen; j++) {
 500         redisAssert(listTypeNext(li,&entry));
 501         value = listTypeGet(&entry);
 502         addReplyBulk(c,value);
 503         decrRefCount(value);
 504     }
 505     listTypeReleaseIterator(li);
 506 }
 507
 508 void ltrimCommand(redisClient *c) {
 509     robj *o;
 510     int start = atoi(c->argv[2]->ptr);
 511     int end = atoi(c->argv[3]->ptr);
 512     int llen;
 513     int j, ltrim, rtrim;
 514     list *list;
 515     listNode *ln;
 516
 517     if ((o = lookupKeyWriteOrReply(c,c->argv[1],shared.ok)) == NULL ||
 518         checkType(c,o,REDIS_LIST)) return;
 519     llen = listTypeLength(o);
 520
 521     /* convert negative indexes */
 522     if (start < 0) start = llen+start;
 523     if (end < 0) end = llen+end;
 524     if (start < 0) start = 0;
 525
 526     /* Invariant: start >= 0, so this test will be true when end < 0.
 527      * The range is empty when start > end or start >= length. */
 528     if (start > end || start >= llen) {
 529         /* Out of range start or start > end result in empty list */
 530         ltrim = llen;
 531         rtrim = 0;
 532     } else {
 533         if (end >= llen) end = llen-1;
 534         ltrim = start;
 535         rtrim = llen-end-1;
 536     }
 537
 538     /* Remove list elements to perform the trim */
 539     if (o->encoding == REDIS_ENCODING_ZIPLIST) {
 540         o->ptr = ziplistDeleteRange(o->ptr,0,ltrim);
 541         o->ptr = ziplistDeleteRange(o->ptr,-rtrim,rtrim);
 542     } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
 543         list = o->ptr;
 544         for (j = 0; j < ltrim; j++) {
 545             ln = listFirst(list);
 546             listDelNode(list,ln);
 547         }
 548         for (j = 0; j < rtrim; j++) {
 549             ln = listLast(list);
 550             listDelNode(list,ln);
 551         }
 552     } else {
 553         redisPanic("Unknown list encoding");
 554     }
 555     if (listTypeLength(o) == 0) dbDelete(c->db,c->argv[1]);
 556     touchWatchedKey(c->db,c->argv[1]);
 557     server.dirty++;
 558     addReply(c,shared.ok);
 559 }
 560
 561 void lremCommand(redisClient *c) {
 562     robj *subject, *obj = c->argv[3];
 563     int toremove = atoi(c->argv[2]->ptr);
 564     int removed = 0;
 565     listTypeEntry entry;
 566
 567     subject = lookupKeyWriteOrReply(c,c->argv[1],shared.czero);
 568     if (subject == NULL || checkType(c,subject,REDIS_LIST)) return;
 569
 570     /* Make sure obj is raw when we're dealing with a ziplist */
 571     if (subject->encoding == REDIS_ENCODING_ZIPLIST)
 572         obj = getDecodedObject(obj);
 573
 574     listTypeIterator *li;
 575     if (toremove < 0) {
 576         toremove = -toremove;
 577         li = listTypeInitIterator(subject,-1,REDIS_HEAD);
 578     } else {
 579         li = listTypeInitIterator(subject,0,REDIS_TAIL);
 580     }
 581
 582     while (listTypeNext(li,&entry)) {
 583         if (listTypeEqual(&entry,obj)) {
 584             listTypeDelete(&entry);
 585             server.dirty++;
 586             removed++;
 587             if (toremove && removed == toremove) break;
 588         }
 589     }
 590     listTypeReleaseIterator(li);
 591
 592     /* Clean up raw encoded object */
 593     if (subject->encoding == REDIS_ENCODING_ZIPLIST)
 594         decrRefCount(obj);
 595
 596     if (listTypeLength(subject) == 0) dbDelete(c->db,c->argv[1]);
 597     addReplySds(c,sdscatprintf(sdsempty(),":%d\r\n",removed));
 598     if (removed) touchWatchedKey(c->db,c->argv[1]);
 599 }
 600
 601 /* This is the semantic of this command:
 602  *  RPOPLPUSH srclist dstlist:
 603  *   IF LLEN(srclist) > 0
 604  *     element = RPOP srclist
 605  *     LPUSH dstlist element
 606  *     RETURN element
 607  *   ELSE
 608  *     RETURN nil
 609  *   END
 610  *  END
 611  *
 612  * The idea is to be able to get an element from a list in a reliable way
 613  * since the element is not just returned but pushed against another list
 614  * as well. This command was originally proposed by Ezra Zygmuntowicz.
 615  */
 616 void rpoplpushcommand(redisClient *c) {
 617     robj *sobj, *value;
 618     if ((sobj = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
 619         checkType(c,sobj,REDIS_LIST)) return;
 620
 621     if (listTypeLength(sobj) == 0) {
 622         addReply(c,shared.nullbulk);
 623     } else {
 624         robj *dobj = lookupKeyWrite(c->db,c->argv[2]);
 625         if (dobj && checkType(c,dobj,REDIS_LIST)) return;
 626         value = listTypePop(sobj,REDIS_TAIL);
 627
 628         /* Add the element to the target list (unless it's directly
 629          * passed to some BLPOP-ing client */
 630         if (!handleClientsWaitingListPush(c,c->argv[2],value)) {
 631             /* Create the list if the key does not exist */
 632             if (!dobj) {
 633                 dobj = createZiplistObject();
 634                 dbAdd(c->db,c->argv[2],dobj);
 635             }
 636             listTypePush(dobj,value,REDIS_HEAD);
 637         }
 638
 639         /* Send the element to the client as reply as well */
 640         addReplyBulk(c,value);
 641
 642         /* listTypePop returns an object with its refcount incremented */
 643         decrRefCount(value);
 644
 645         /* Delete the source list when it is empty */
 646         if (listTypeLength(sobj) == 0) dbDelete(c->db,c->argv[1]);
 647         touchWatchedKey(c->db,c->argv[1]);
 648         server.dirty++;
 649     }
 650 }
 651
 652 /*-----------------------------------------------------------------------------
 653  * Blocking POP operations
 654  *----------------------------------------------------------------------------*/
 655
 656 /* Currently Redis blocking operations support is limited to list POP ops,
 657  * so the current implementation is not fully generic, but it is also not
 658  * completely specific so it will not require a rewrite to support new
 659  * kind of blocking operations in the future.
 660  *
 661  * Still it's important to note that list blocking operations can be already
 662  * used as a notification mechanism in order to implement other blocking
 663  * operations at application level, so there must be a very strong evidence
 664  * of usefulness and generality before new blocking operations are implemented.
 665  *
 666  * This is how the current blocking POP works, we use BLPOP as example:
 667  * - If the user calls BLPOP and the key exists and contains a non empty list
 668  *   then LPOP is called instead. So BLPOP is semantically the same as LPOP
 669  *   if there is not to block.
 670  * - If instead BLPOP is called and the key does not exists or the list is
 671  *   empty we need to block. In order to do so we remove the notification for
 672  *   new data to read in the client socket (so that we'll not serve new
 673  *   requests if the blocking request is not served). Also we put the client
 674  *   in a dictionary (db->blocking_keys) mapping keys to a list of clients
 675  *   blocking for this keys.
 676  * - If a PUSH operation against a key with blocked clients waiting is
 677  *   performed, we serve the first in the list: basically instead to push
 678  *   the new element inside the list we return it to the (first / oldest)
 679  *   blocking client, unblock the client, and remove it form the list.
 680  *
 681  * The above comment and the source code should be enough in order to understand
 682  * the implementation and modify / fix it later.
 683  */
 684
 685 /* Set a client in blocking mode for the specified key, with the specified
 686  * timeout */
 687 void blockForKeys(redisClient *c, robj **keys, int numkeys, time_t timeout) {
 688     dictEntry *de;
 689     list *l;
 690     int j;
 691
 692     c->blocking_keys = zmalloc(sizeof(robj*)*numkeys);
 693     c->blocking_keys_num = numkeys;
 694     c->blockingto = timeout;
 695     for (j = 0; j < numkeys; j++) {
 696         /* Add the key in the client structure, to map clients -> keys */
 697         c->blocking_keys[j] = keys[j];
 698         incrRefCount(keys[j]);
 699
 700         /* And in the other "side", to map keys -> clients */
 701         de = dictFind(c->db->blocking_keys,keys[j]);
 702         if (de == NULL) {
 703             int retval;
 704
 705             /* For every key we take a list of clients blocked for it */
 706             l = listCreate();
 707             retval = dictAdd(c->db->blocking_keys,keys[j],l);
 708             incrRefCount(keys[j]);
 709             redisAssert(retval == DICT_OK);
 710         } else {
 711             l = dictGetEntryVal(de);
 712         }
 713         listAddNodeTail(l,c);
 714     }
 715     /* Mark the client as a blocked client */
 716     c->flags |= REDIS_BLOCKED;
 717     server.blpop_blocked_clients++;
 718 }
 719
 720 /* Unblock a client that's waiting in a blocking operation such as BLPOP */
 721 void unblockClientWaitingData(redisClient *c) {
 722     dictEntry *de;
 723     list *l;
 724     int j;
 725
 726     redisAssert(c->blocking_keys != NULL);
 727     /* The client may wait for multiple keys, so unblock it for every key. */
 728     for (j = 0; j < c->blocking_keys_num; j++) {
 729         /* Remove this client from the list of clients waiting for this key. */
 730         de = dictFind(c->db->blocking_keys,c->blocking_keys[j]);
 731         redisAssert(de != NULL);
 732         l = dictGetEntryVal(de);
 733         listDelNode(l,listSearchKey(l,c));
 734         /* If the list is empty we need to remove it to avoid wasting memory */
 735         if (listLength(l) == 0)
 736             dictDelete(c->db->blocking_keys,c->blocking_keys[j]);
 737         decrRefCount(c->blocking_keys[j]);
 738     }
 739     /* Cleanup the client structure */
 740     zfree(c->blocking_keys);
 741     c->blocking_keys = NULL;
 742     c->flags &= (~REDIS_BLOCKED);
 743     server.blpop_blocked_clients--;
 744     /* We want to process data if there is some command waiting
 745      * in the input buffer. Note that this is safe even if
 746      * unblockClientWaitingData() gets called from freeClient() because
 747      * freeClient() will be smart enough to call this function
 748      * *after* c->querybuf was set to NULL. */
 749     if (c->querybuf && sdslen(c->querybuf) > 0) processInputBuffer(c);
 750 }
 751
 752 /* This should be called from any function PUSHing into lists.
 753  * 'c' is the "pushing client", 'key' is the key it is pushing data against,
 754  * 'ele' is the element pushed.
 755  *
 756  * If the function returns 0 there was no client waiting for a list push
 757  * against this key.
 758  *
 759  * If the function returns 1 there was a client waiting for a list push
 760  * against this key, the element was passed to this client thus it's not
 761  * needed to actually add it to the list and the caller should return asap. */
 762 int handleClientsWaitingListPush(redisClient *c, robj *key, robj *ele) {
 763     struct dictEntry *de;
 764     redisClient *receiver;
 765     list *l;
 766     listNode *ln;
 767
 768     de = dictFind(c->db->blocking_keys,key);
 769     if (de == NULL) return 0;
 770     l = dictGetEntryVal(de);
 771     ln = listFirst(l);
 772     redisAssert(ln != NULL);
 773     receiver = ln->value;
 774
 775     addReplySds(receiver,sdsnew("*2\r\n"));
 776     addReplyBulk(receiver,key);
 777     addReplyBulk(receiver,ele);
 778     unblockClientWaitingData(receiver);
 779     return 1;
 780 }
 781
 782 /* Blocking RPOP/LPOP */
 783 void blockingPopGenericCommand(redisClient *c, int where) {
 784     robj *o;
 785     time_t timeout;
 786     int j;
 787
 788     for (j = 1; j < c->argc-1; j++) {
 789         o = lookupKeyWrite(c->db,c->argv[j]);
 790         if (o != NULL) {
 791             if (o->type != REDIS_LIST) {
 792                 addReply(c,shared.wrongtypeerr);
 793                 return;
 794             } else {
 795                 if (listTypeLength(o) != 0) {
 796                     /* If the list contains elements fall back to the usual
 797                      * non-blocking POP operation */
 798                     robj *argv[2], **orig_argv;
 799                     int orig_argc;
 800
 801                     /* We need to alter the command arguments before to call
 802                      * popGenericCommand() as the command takes a single key. */
 803                     orig_argv = c->argv;
 804                     orig_argc = c->argc;
 805                     argv[1] = c->argv[j];
 806                     c->argv = argv;
 807                     c->argc = 2;
 808
 809                     /* Also the return value is different, we need to output
 810                      * the multi bulk reply header and the key name. The
 811                      * "real" command will add the last element (the value)
 812                      * for us. If this souds like an hack to you it's just
 813                      * because it is... */
 814                     addReplySds(c,sdsnew("*2\r\n"));
 815                     addReplyBulk(c,argv[1]);
 816                     popGenericCommand(c,where);
 817
 818                     /* Fix the client structure with the original stuff */
 819                     c->argv = orig_argv;
 820                     c->argc = orig_argc;
 821                     return;
 822                 }
 823             }
 824         }
 825     }
 826     /* If the list is empty or the key does not exists we must block */
 827     timeout = strtol(c->argv[c->argc-1]->ptr,NULL,10);
 828     if (timeout > 0) timeout += time(NULL);
 829     blockForKeys(c,c->argv+1,c->argc-2,timeout);
 830 }
 831
 832 void blpopCommand(redisClient *c) {
 833     blockingPopGenericCommand(c,REDIS_HEAD);
 834 }
 835
 836 void brpopCommand(redisClient *c) {
 837     blockingPopGenericCommand(c,REDIS_TAIL);
 838 }