queue(7) - man - phpMan

QUEUE(7)                              Linux Programmer's Manual                             QUEUE(7)



NAME
       queue - implementations of linked lists and queues

DESCRIPTION
       The <sys/queue.h> header file provides a set of macros that define and operate on the follow‐
       ing data structures:

       *  singly linked lists (SLIST)

       *  doubly linked lists (LIST)

       *  singly linked tail queues (STAILQ)

       *  doubly linked tail queues (TAILQ)

       *  doubly linked circular queues (CIRCLEQ)

       All structures support the following functionality:

       *  Insertion of a new entry at the head of the list.

       *  Insertion of a new entry after any element in the list.

       *  O(1) removal of an entry from the head of the list.

       *  Forward traversal through the list.

       Code size and execution time depend on the complexity of the data structure  being  used,  so
       programmers should take care to choose the appropriate one.

   Singly linked lists (SLIST)
       Singly linked lists are the simplest and support only the above functionality.  Singly linked
       lists are ideal for applications with large datasets and few or no removals,  or  for  imple‐
       menting a LIFO queue.  Singly linked lists add the following functionality:

       *  O(n) removal of any entry in the list.

   Singly linked tail queues (STAILQ)
       Singly linked tail queues add the following functionality:

       *  Entries can be added at the end of a list.

       *  O(n) removal of any entry in the list.

       *  They may be concatenated.

       However:

       *  All list insertions must specify the head of the list.

       *  Each head entry requires two pointers rather than one.

       Singly  linked  tail  queues are ideal for applications with large datasets and few or no re‐
       movals, or for implementing a FIFO queue.

   Doubly linked data structures
       All doubly linked types of data structures (lists and tail queues) additionally allow:

       *  Insertion of a new entry before any element in the list.

       *  O(1) removal of any entry in the list.

       However:

       *  Each element requires two pointers rather than one.

   Doubly linked lists (LIST)
       Linked lists are the simplest of the doubly linked data structures.  They add  the  following
       functionality over the above:

       *  They may be traversed backwards.

       However:

       *  To  traverse  backwards,  an entry to begin the traversal and the list in which it is con‐
          tained must be specified.

   Doubly linked tail queues (TAILQ)
       Tail queues add the following functionality:

       *  Entries can be added at the end of a list.

       *  They may be traversed backwards, from tail to head.

       *  They may be concatenated.

       However:

       *  All list insertions and removals must specify the head of the list.

       *  Each head entry requires two pointers rather than one.

   Doubly linked circular queues (CIRCLEQ)
       Circular queues add the following functionality over the above:

       *  The first and last entries are connected.

       However:

       *  The termination condition for traversal is more complex.

CONFORMING TO
       Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008.  Present on  the  BSDs.   <sys/queue.h>  macros
       first appeared in 4.4BSD.

SEE ALSO
       circleq(3), insque(3), list(3), slist(3), stailq(3), tailq(3)

COLOPHON
       This  page  is  part  of  release  5.10 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of this page, can be  found
       at https://www.kernel.org/doc/man-pages/.



GNU                                          2020-11-16                                     QUEUE(7)