man3/queue.3

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  32 .\"     @(#)queue.3     8.2 (Berkeley) 1/24/94
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  34 .\" hch, 2002-03-25
  35 .\" 2007-12-08, mtk, Converted from mdoc to man macros
  36 .\"
  37 .TH QUEUE 3 2007-12-08 "Linux" "Linux Programmer's Manual"
  38 .SH NAME
  39 LIST_ENTRY, LIST_HEAD, LIST_INIT, LIST_INSERT_AFTER, \
  40 LIST_INSERT_HEAD, LIST_REMOVE, TAILQ_ENTRY, TAILQ_HEAD, \
  41 TAILQ_INIT, TAILQ_INSERT_AFTER, TAILQ_INSERT_HEAD, TAILQ_INSERT_TAIL, \
  42 TAILQ_REMOVE, CIRCLEQ_ENTRY, CIRCLEQ_HEAD, CIRCLEQ_INIT, \
  43 CIRCLEQ_INSERT_AFTER, CIRCLEQ_INSERT_BEFORE, \
  44 CIRCLEQ_INSERT_HEAD, CIRCLEQ_INSERT_TAIL, \
  45 CIRCLEQ_REMOVE \- implementations of lists, tail queues, and circular queues
  46 .SH SYNOPSIS
  47 .nf
  48 .B #include <sys/queue.h>
  49
  50 .BI "LIST_ENTRY(" TYPE );
  51 .BI "LIST_HEAD(" HEADNAME ", " TYPE );
  52 .BI "LIST_INIT(LIST_HEAD *" head );
  53 .BI "LIST_INSERT_AFTER(LIST_ENTRY *" listelm ", "
  54 .BI "                TYPE *" elm ", LIST_ENTRY " NAME );
  55 .BI "LIST_INSERT_HEAD(LIST_HEAD *" head ", "
  56 .BI "                TYPE *" elm ", LIST_ENTRY " NAME );
  57 .BI "LIST_REMOVE(TYPE *" elm ", LIST_ENTRY " NAME );
  58
  59 .BI "TAILQ_ENTRY(" TYPE );
  60 .BI "TAILQ_HEAD("HEADNAME ", " TYPE );
  61 .BI "TAILQ_INIT(TAILQ_HEAD *" head );
  62 .BI "TAILQ_INSERT_AFTER(TAILQ_HEAD *" head ", TYPE *" listelm ", "
  63 .BI "                TYPE *" elm ", TAILQ_ENTRY " NAME );
  64 .BI "TAILQ_INSERT_HEAD(TAILQ_HEAD *" head ", "
  65 .BI "                TYPE *" elm ", TAILQ_ENTRY " NAME );
  66 .BI "TAILQ_INSERT_TAIL(TAILQ_HEAD *" head ", "
  67 .BI "                TYPE *" elm ", TAILQ_ENTRY " NAME );
  68 .BI "TAILQ_REMOVE(TAILQ_HEAD *" head ", TYPE *" elm ", TAILQ_ENTRY " NAME );
  69
  70 .BI CIRCLEQ_ENTRY( TYPE );
  71 .BI "CIRCLEQ_HEAD(" HEADNAME ", " TYPE );
  72 .BI "CIRCLEQ_INIT(CIRCLEQ_HEAD *" head );
  73 .BI "CIRCLEQ_INSERT_AFTER(CIRCLEQ_HEAD *" head ", TYPE *" listelm ", "
  74 .BI "                TYPE *" elm ", CIRCLEQ_ENTRY " NAME );
  75 .BI "CIRCLEQ_INSERT_BEFORE(CIRCLEQ_HEAD *" head ", TYPE *" listelm ", "
  76 .BI "                TYPE *" elm ", CIRCLEQ_ENTRY " NAME );
  77 .BI "CIRCLEQ_INSERT_HEAD(CIRCLEQ_HEAD *" head ", "
  78 .BI "                TYPE *" elm ", CIRCLEQ_ENTRY " NAME );
  79 .BI "CIRCLEQ_INSERT_TAIL(CIRCLEQ_HEAD *" head ", "
  80 .BI "                TYPE *" elm ", CIRCLEQ_ENTRY " NAME );
  81 .BI "CIRCLEQ_REMOVE(CIRCLEQ_HEAD *" head ", "
  82 .BI "                TYPE *" elm ", CIRCLEQ_ENTRY " NAME );
  83 .fi
  84 .SH DESCRIPTION
  85 These macros define and operate on three types of data structures:
  86 lists, tail queues, and circular queues.
  87 All three structures support the following functionality:
  88 .RS
  89 .IP 1. 4
  90 Insertion of a new entry at the head of the list.
  91 .IP 2.
  92 Insertion of a new entry after any element in the list.
  93 .IP 3.
  94 Removal of any entry in the list.
  95 .IP 4.
  96 Forward traversal through the list.
  97 .RE
  98 .PP
  99 Lists are the simplest of the three data structures and support
 100 only the above functionality.
 101
 102 Tail queues add the following functionality:
 103 .RS
 104 .IP 1. 4
 105 Entries can be added at the end of a list.
 106 .RE
 107 .PP
 108 However:
 109 .RS
 110 .IP 1. 4
 111 All list insertions and removals must specify the head of the list.
 112 .IP 2.
 113 Each head entry requires two pointers rather than one.
 114 .IP 3.
 115 Code size is about 15% greater and operations run about 20% slower
 116 than lists.
 117 .RE
 118 .PP
 119 Circular queues add the following functionality:
 120 .RS
 121 .IP 1. 4
 122 Entries can be added at the end of a list.
 123 .IP 2.
 124 Entries can be added before another entry.
 125 .IP 3.
 126 They may be traversed backwards, from tail to head.
 127 .RE
 128 .PP
 129 However:
 130 .RS
 131 .IP 1. 4
 132 All list insertions and removals must specify the head of the list.
 133 .IP 2.
 134 Each head entry requires two pointers rather than one.
 135 .IP 3.
 136 The termination condition for traversal is more complex.
 137 .IP 4.
 138 Code size is about 40% greater and operations run about 45% slower
 139 than lists.
 140 .RE
 141 .PP
 142 In the macro definitions,
 143 .I TYPE
 144 is the name of a user defined structure,
 145 that must contain a field of type
 146 .IR "LIST_ENTRY" ,
 147 .IR "TAILQ_ENTRY" ,
 148 or
 149 .IR "CIRCLEQ_ENTRY" ,
 150 named
 151 .IR NAME .
 152 The argument
 153 .I HEADNAME
 154 is the name of a user defined structure that must be declared
 155 using the macros
 156 .IR "LIST_HEAD" ,
 157 .IR "TAILQ_HEAD" ,
 158 or
 159 .IR "CIRCLEQ_HEAD" .
 160 See the examples below for further explanation of how these
 161 macros are used.
 162 .SS Lists
 163 A list is headed by a structure defined by the
 164 LIST_HEAD macro.
 165 This structure contains a single pointer to the first element
 166 on the list.
 167 The elements are doubly linked so that an arbitrary element can be
 168 removed without traversing the list.
 169 New elements can be added to the list after an existing element or
 170 at the head of the list.
 171 A
 172 .I LIST_HEAD
 173 structure is declared as follows:
 174 .in +4n
 175 .nf
 176
 177 LIST_HEAD(HEADNAME, TYPE) head;
 178 .fi
 179 .in
 180 .sp
 181 where
 182 .I HEADNAME
 183 is the name of the structure to be defined, and
 184 .I TYPE
 185 is the type of the elements to be linked into the list.
 186 A pointer to the head of the list can later be declared as:
 187 .in +4n
 188 .nf
 189
 190 struct HEADNAME *headp;
 191 .fi
 192 .in
 193 .sp
 194 (The names
 195 .IR "head"
 196 and
 197 .IR "headp"
 198 are user selectable.)
 199 .sp
 200 The macro
 201 .B LIST_ENTRY
 202 declares a structure that connects the elements in
 203 the list.
 204 .sp
 205 The macro
 206 .B LIST_INIT
 207 initializes the list referenced by
 208 .IR head .
 209 .sp
 210 The macro
 211 .B LIST_INSERT_HEAD
 212 inserts the new element
 213 .I elm
 214 at the head of the list.
 215 .sp
 216 The macro
 217 .B LIST_INSERT_AFTER
 218 inserts the new element
 219 .I elm
 220 after the element
 221 .IR listelm .
 222 .sp
 223 The macro
 224 .B LIST_REMOVE
 225 removes the element
 226 .I elm
 227 from the list.
 228 .SS List Example
 229 .nf
 230 LIST_HEAD(listhead, entry) head;
 231 struct listhead *headp;                 /* List head. */
 232 struct entry {
 233     ...
 234     LIST_ENTRY(entry) entries;          /* List. */
 235     ...
 236 } *n1, *n2, *np;
 237
 238 LIST_INIT(&head);                       /* Initialize the list. */
 239
 240 n1 = malloc(sizeof(struct entry));      /* Insert at the head. */
 241 LIST_INSERT_HEAD(&head, n1, entries);
 242
 243 n2 = malloc(sizeof(struct entry));      /* Insert after. */
 244 LIST_INSERT_AFTER(n1, n2, entries);
 245                                         /* Forward traversal. */
 246 for (np = head.lh_first; np != NULL; np = np\->entries.le_next)
 247     np\-> ...
 248
 249 while (head.lh_first != NULL)           /* Delete. */
 250     LIST_REMOVE(head.lh_first, entries);
 251 .fi
 252 .SS Tail Queues
 253 A tail queue is headed by a structure defined by the
 254 TAILQ_HEAD macro.
 255 This structure contains a pair of pointers,
 256 one to the first element in the tail queue and the other to
 257 the last element in the tail queue.
 258 The elements are doubly linked so that an arbitrary element can be
 259 removed without traversing the tail queue.
 260 New elements can be added to the tail queue after an existing element,
 261 at the head of the tail queue, or at the end of the tail queue.
 262 A
 263 .I TAILQ_HEAD
 264 structure is declared as follows:
 265 .in +4n
 266 .nf
 267
 268 TAILQ_HEAD(HEADNAME, TYPE) head;
 269 .fi
 270 .in
 271 .PP
 272 where
 273 .IR "HEADNAME"
 274 is the name of the structure to be defined, and
 275 .IR "TYPE"
 276 is the type of the elements to be linked into the tail queue.
 277 A pointer to the head of the tail queue can later be declared as:
 278 .in +4n
 279 .nf
 280
 281 struct HEADNAME *headp;
 282 .fi
 283 .in
 284 .sp
 285 (The names
 286 .IR "head"
 287 and
 288 .IR "headp"
 289 are user selectable.)
 290 .sp
 291 The macro
 292 .B TAILQ_ENTRY
 293 declares a structure that connects the elements in
 294 the tail queue.
 295 .sp
 296 The macro
 297 .B TAILQ_INIT
 298 initializes the tail queue referenced by
 299 .IR head .
 300 .sp
 301 The macro
 302 .B TAILQ_INSERT_HEAD
 303 inserts the new element
 304 .I elm
 305 at the head of the tail queue.
 306 .sp
 307 The macro
 308 .B TAILQ_INSERT_TAIL
 309 inserts the new element
 310 .I elm
 311 at the end of the tail queue.
 312 .sp
 313 The macro
 314 .B TAILQ_INSERT_AFTER
 315 inserts the new element
 316 .I elm
 317 after the element
 318 .IR listelm .
 319 .sp
 320 The macro
 321 .B TAILQ_REMOVE
 322 removes the element
 323 .I elm
 324 from the tail queue.
 325 .SS Tail Queue Example
 326 .nf
 327 TAILQ_HEAD(tailhead, entry) head;
 328 struct tailhead *headp;                 /* Tail queue head. */
 329 struct entry {
 330     ...
 331     TAILQ_ENTRY(entry) entries;         /* Tail queue. */
 332     ...
 333 } *n1, *n2, *np;
 334
 335 TAILQ_INIT(&head);                      /* Initialize the queue. */
 336
 337 n1 = malloc(sizeof(struct entry));      /* Insert at the head. */
 338 TAILQ_INSERT_HEAD(&head, n1, entries);
 339
 340 n1 = malloc(sizeof(struct entry));      /* Insert at the tail. */
 341 TAILQ_INSERT_TAIL(&head, n1, entries);
 342
 343 n2 = malloc(sizeof(struct entry));      /* Insert after. */
 344 TAILQ_INSERT_AFTER(&head, n1, n2, entries);
 345                                         /* Forward traversal. */
 346 for (np = head.tqh_first; np != NULL; np = np->entries.tqe_next)
 347     np-> ...
 348                                         /* Delete. */
 349 while (head.tqh_first != NULL)
 350     TAILQ_REMOVE(&head, head.tqh_first, entries);
 351 .fi
 352 .SS Circular Queues
 353 A circular queue is headed by a structure defined by the
 354 CIRCLEQ_HEAD macro.
 355 This structure contains a pair of pointers,
 356 one to the first element in the circular queue and the other to the
 357 last element in the circular queue.
 358 The elements are doubly linked so that an arbitrary element can be
 359 removed without traversing the queue.
 360 New elements can be added to the queue after an existing element,
 361 before an existing element, at the head of the queue, or at the end
 362 of the queue.
 363 A
 364 .I CIRCLEQ_HEAD
 365 structure is declared as follows:
 366 .in +4n
 367 .nf
 368
 369 CIRCLEQ_HEAD(HEADNAME, TYPE) head;
 370 .fi
 371 .in
 372 .sp
 373 where
 374 .IR "HEADNAME"
 375 is the name of the structure to be defined, and
 376 .IR "TYPE"
 377 is the type of the elements to be linked into the circular queue.
 378 A pointer to the head of the circular queue can later be declared as:
 379 .in +4n
 380 .nf
 381
 382 struct HEADNAME *headp;
 383 .fi
 384 .in
 385 .sp
 386 (The names
 387 .IR "head"
 388 and
 389 .IR "headp"
 390 are user selectable.)
 391 .sp
 392 The macro
 393 .B CIRCLEQ_ENTRY
 394 declares a structure that connects the elements in
 395 the circular queue.
 396 .sp
 397 The macro
 398 .B CIRCLEQ_INIT
 399 initializes the circular queue referenced by
 400 .IR head .
 401 .sp
 402 The macro
 403 .B CIRCLEQ_INSERT_HEAD
 404 inserts the new element
 405 .I elm
 406 at the head of the circular queue.
 407 .sp
 408 The macro
 409 .B CIRCLEQ_INSERT_TAIL
 410 inserts the new element
 411 .I elm
 412 at the end of the circular queue.
 413 .sp
 414 The macro
 415 .B CIRCLEQ_INSERT_AFTER
 416 inserts the new element
 417 .I elm
 418 after the element
 419 .IR listelm .
 420 .sp
 421 The macro
 422 .B CIRCLEQ_INSERT_BEFORE
 423 inserts the new element
 424 .I elm
 425 before the element
 426 .IR listelm .
 427 .sp
 428 The macro
 429 .B CIRCLEQ_REMOVE
 430 removes the element
 431 .I elm
 432 from the circular queue.
 433 .SS Circular Queue Example
 434 .nf
 435 CIRCLEQ_HEAD(circleq, entry) head;
 436 struct circleq *headp;              /* Circular queue head. */
 437 struct entry {
 438     ...
 439     CIRCLEQ_ENTRY(entry) entries;   /* Circular queue. */
 440     ...
 441 } *n1, *n2, *np;
 442
 443 CIRCLEQ_INIT(&head);                /* Initialize the circular queue. */
 444
 445 n1 = malloc(sizeof(struct entry));  /* Insert at the head. */
 446 CIRCLEQ_INSERT_HEAD(&head, n1, entries);
 447
 448 n1 = malloc(sizeof(struct entry));  /* Insert at the tail. */
 449 CIRCLEQ_INSERT_TAIL(&head, n1, entries);
 450
 451 n2 = malloc(sizeof(struct entry));  /* Insert after. */
 452 CIRCLEQ_INSERT_AFTER(&head, n1, n2, entries);
 453
 454 n2 = malloc(sizeof(struct entry));  /* Insert before. */
 455 CIRCLEQ_INSERT_BEFORE(&head, n1, n2, entries);
 456                                     /* Forward traversal. */
 457 for (np = head.cqh_first; np != (void *)&head;
 458         np = np->entries.cqe_next)
 459     np-> ...
 460                                     /* Reverse traversal. */
 461 for (np = head.cqh_last; np != (void *)&head; np = np->entries.cqe_prev)
 462     np-> ...
 463                                     /* Delete. */
 464 while (head.cqh_first != (void *)&head)
 465     CIRCLEQ_REMOVE(&head, head.cqh_first, entries);
 466 .fi
 467 .SH "CONFORMING TO"
 468 Not in POSIX.1-2001.
 469 Present on the BSDs.
 470 The
 471 queue functions first appeared in
 472 4.4BSD.