GCQ(3) | Library Functions Manual | GCQ(3)

# NAME

`GCQ_INIT`, `GCQ_INIT_HEAD`, `gcq_init`, `gcq_init_head`, `gcq_q`, `gcq_hq`, `gcq_head`, `gcq_remove`, `gcq_onlist`, `gcq_empty`, `gcq_linked`, `gcq_insert_after`, `gcq_insert_before`, `gcq_insert_head`, `gcq_insert_tail`, `gcq_tie`, `gcq_tie_after`, `gcq_tie_before`, `gcq_merge`, `gcq_merge_head`, `gcq_merge_tail`, `gcq_clear`, `gcq_remove_all`, `GCQ_ITEM`, `GCQ_GOT_FIRST`, `GCQ_GOT_LAST`, `GCQ_GOT_NEXT`, `GCQ_GOT_PREV`, `GCQ_DEQUEUED_FIRST`, `GCQ_DEQUEUED_LAST`, `GCQ_DEQUEUED_NEXT`, `GCQ_DEQUEUED_PREV`, `GCQ_GOT_FIRST_TYPED`, `GCQ_GOT_LAST_TYPED`, `GCQ_GOT_NEXT_TYPED`, `GCQ_GOT_PREV_TYPED`, `GCQ_DEQUEUED_FIRST_TYPED`, `GCQ_DEQUEUED_LAST_TYPED`, `GCQ_DEQUEUED_NEXT_TYPED`, `GCQ_DEQUEUED_PREV_TYPED`, `GCQ_GOT_FIRST_COND`, `GCQ_GOT_LAST_COND`, `GCQ_GOT_NEXT_COND`, `GCQ_GOT_PREV_COND`, `GCQ_DEQUEUED_FIRST_COND`, `GCQ_DEQUEUED_LAST_COND`, `GCQ_DEQUEUED_NEXT_COND`, `GCQ_DEQUEUED_PREV_COND`, `GCQ_GOT_FIRST_COND_TYPED`, `GCQ_GOT_LAST_COND_TYPED`, `GCQ_GOT_NEXT_COND_TYPED`, `GCQ_GOT_PREV_COND_TYPED`, `GCQ_DEQUEUED_FIRST_COND_TYPED`, `GCQ_DEQUEUED_LAST_COND_TYPED`, `GCQ_DEQUEUED_NEXT_COND_TYPED`, `GCQ_DEQUEUED_PREV_COND_TYPED`, `GCQ_FOREACH`, `GCQ_FOREACH_REV`, `GCQ_FOREACH_NVAR`, `GCQ_FOREACH_NVAR_REV`, `GCQ_FOREACH_RO`, `GCQ_FOREACH_RO_REV`, `GCQ_FOREACH_DEQUEUED`, `GCQ_FOREACH_DEQUEUED_REV`, `GCQ_FOREACH_TYPED`, `GCQ_FOREACH_REV_TYPED`, `GCQ_FOREACH_NVAR_TYPED`, `GCQ_FOREACH_NVAR_REV_TYPED`, `GCQ_FOREACH_RO_TYPED`, `GCQ_FOREACH_RO_REV_TYPED`, `GCQ_FOREACH_DEQUEUED_TYPED`, `GCQ_FOREACH_DEQUEUED_REV_TYPED`, `GCQ_FIND`, `GCQ_FIND_REV`, `GCQ_FIND_TYPED`, `GCQ_FIND_REV_TYPED` —
Generic Circular Queues

# SYNOPSIS

`#include <sys/gcq.h>`

struct gcq;
struct gcq_head;

`GCQ_INIT`(name);

`GCQ_INIT_HEAD`(name);

static inline void
`gcq_init`(struct gcq *q);

static inline void
`gcq_init_head`(struct gcq_head *head);

static inline struct gcq *
`gcq_q`(struct gcq_head *head);

static inline struct gcq *
`gcq_hq`(struct gcq_head *head);

static inline struct gcq_head *
`gcq_head`(struct gcq *q);

static inline struct gcq *
`gcq_remove`(struct gcq *q);

static inline bool
`gcq_onlist`(struct gcq *q);

static inline bool
`gcq_empty`(struct gcq_head *head);

static inline bool
`gcq_linked`(struct gcq *prev, struct gcq *next);

static inline void
`gcq_insert_after`(struct gcq *on, struct gcq *off);

static inline void
`gcq_insert_before`(struct gcq *on, struct gcq *off);

static inline void
`gcq_insert_head`(struct gcq_head *head, struct gcq *q);

static inline void
`gcq_insert_tail`(struct gcq_head *head, struct gcq *q);

static inline void
`gcq_tie`(struct gcq *dst, struct gcq *src);

static inline void
`gcq_tie_after`(struct gcq *dst, struct gcq *src);

static inline void
`gcq_tie_before`(struct gcq *dst, struct gcq *src);

static inline void
`gcq_merge`(struct gcq *dst, struct gcq *src);

static inline void
`gcq_merge_tail`(struct gcq_head *dst, struct gcq_head *src);

static inline void
`gcq_merge_head`(struct gcq_head *dst, struct gcq_head *src);

static inline void
`gcq_clear`(struct gcq *q);

static inline void
`gcq_remove_all`(struct gcq_head *head);

type *
`GCQ_ITEM`(q, type, name);

bool
`GCQ_GOT_FIRST`(var, head);

bool
`GCQ_GOT_LAST`(var, head);

bool
`GCQ_GOT_NEXT`(var, current, head, start);

bool
`GCQ_GOT_PREV`(var, current, head, start);

bool
`GCQ_DEQUEUED_FIRST`(var, head);

bool
`GCQ_DEQUEUED_LAST`(var, head);

bool
`GCQ_DEQUEUED_NEXT`(var, current, head, start);

bool
`GCQ_DEQUEUED_PREV`(var, current, head, start);

bool
`GCQ_GOT_FIRST_TYPED`(tvar, head, type, name);

bool
`GCQ_GOT_LAST_TYPED`(tvar, head, type, name);

bool
`GCQ_GOT_NEXT_TYPED`(tvar, current, head, start, type, name);

bool
`GCQ_GOT_PREV_TYPED`(tvar, current, head, start, type, name);

bool
`GCQ_DEQUEUED_FIRST_TYPED`(tvar, head, type, name);

bool
`GCQ_DEQUEUED_LAST_TYPED`(tvar, head, type, name);

bool
`GCQ_DEQUEUED_NEXT_TYPED`(tvar, current, head, start, type, name);

bool
`GCQ_DEQUEUED_PREV_TYPED`(tvar, current, head, start, type, name);

bool
`GCQ_GOT_FIRST_COND`(var, head, cond);

bool
`GCQ_GOT_LAST_COND`(var, head, cond);

bool
`GCQ_GOT_NEXT_COND`(var, current, head, start, cond);

bool
`GCQ_GOT_PREV_COND`(var, current, head, start, cond);

bool
`GCQ_DEQUEUED_FIRST_COND`(var, head, cond);

bool
`GCQ_DEQUEUED_LAST_COND`(var, head, cond);

bool
`GCQ_DEQUEUED_NEXT_COND`(var, current, head, start, cond);

bool
`GCQ_DEQUEUED_PREV_COND`(var, current, head, start, cond);

bool
`GCQ_GOT_FIRST_COND_TYPED`(tvar, head, type, name, cond);

bool
`GCQ_GOT_LAST_COND_TYPED`(tvar, head, type, name, cond);

bool
`GCQ_GOT_NEXT_COND_TYPED`(tvar, current, head, start, type, name, cond);

bool
`GCQ_GOT_PREV_COND_TYPED`(tvar, current, head, start, type, name, cond);

bool
`GCQ_DEQUEUED_FIRST_COND_TYPED`(tvar, head, type, name, cond);

bool
`GCQ_DEQUEUED_LAST_COND_TYPED`(tvar, head, type, name, cond);

bool
`GCQ_DEQUEUED_NEXT_COND_TYPED`(tvar, current, head, start, type, name, cond);

bool
`GCQ_DEQUEUED_PREV_COND_TYPED`(tvar, current, head, start, type, name, cond);

`GCQ_FOREACH`(var, head);

`GCQ_FOREACH_REV`(var, head);

`GCQ_FOREACH_NVAR`(var, nvar, head);

`GCQ_FOREACH_NVAR_REV`(var, nvar, head);

`GCQ_FOREACH_RO`(var, nvar, head);

`GCQ_FOREACH_RO_REV`(var, nvar, head);

`GCQ_FOREACH_DEQUEUED`(var, nvar, head);

`GCQ_FOREACH_DEQUEUED_REV`(var, nvar, head);

`GCQ_FOREACH_TYPED`(var, head, tvar, type, name);

`GCQ_FOREACH_REV_TYPED`(var, head, tvar, type, name);

`GCQ_FOREACH_NVAR_TYPED`(var, nvar, head, tvar, type, name);

`GCQ_FOREACH_NVAR_REV_TYPED`(var, nvar, head, tvar, type, name);

`GCQ_FOREACH_RO_TYPED`(var, nvar, head, tvar, type, name);

`GCQ_FOREACH_RO_REV_TYPED`(var, nvar, head, tvar, type, name);

`GCQ_FOREACH_DEQUEUED_TYPED`(var, nvar, head, tvar, type, name);

`GCQ_FOREACH_DEQUEUED_REV_TYPED`(var, nvar, head, tvar, type, name);

`GCQ_FIND`(var, head, cond);

`GCQ_FIND_REV`(var, head, cond);

`GCQ_FIND_TYPED`(var, head, tvar, type, name, cond);

`GCQ_FIND_REV_TYPED`(var, head, tvar, type, name, cond);

`GCQ_ASSERT`(cond);

# DESCRIPTION

The generic circular queue is a doubly linked list designed for efficient merge operations and unconditional removal. All basic operations can be performed with or without use of a separate head, allowing easy replacement of any pointers where efficient removal is desired. The meaning of the data type will not change; direct use and defined operations can be mixed when convenient. The basic type is:

    struct gcq {
    	struct gcq *q_next;
    	struct gcq *q_prev;
    };

The structure must first be initialized such that the q_next and q_prev members point to the beginning of the struct gcq. This can be done with `gcq_init`() and `gcq_init_head`() or with constant initializers `GCQ_INIT`() and `GCQ_INIT_HEAD`(). A struct gcq should never be given `NULL` values.

The structure containing the struct gcq can be retrieved by pointer arithmetic in the `GCQ_ITEM`() macro. List traversal normally requires knowledge of the list head to safely retrieve list items.

Capitalized operation names are macros and should be assumed to cause multiple evaluation of arguments. `TYPED` variants of macros set a typed pointer variable instead of or in addition to struct gcq * arguments. Additional type specific inlines and macros around some GCQ operations can be useful.

A few assertions are provided when `DIAGNOSTIC` is defined in the kernel or `_DIAGNOSTIC` is defined in userland. If `GCQ_USE_ASSERT` is defined prior to header inclusions then `assert`() will be used for assertions and `NDEBUG` can be used to turn them off. `GCQ_ASSERT`() is a wrapper around the used assertion function. None of the operations accept `NULL` arguments, however this is not tested by assertion.

The head is separately named for type checking but contains only a struct gcq, a pointer to which can be retrieved via `gcq_hq`(). The reverse operation is performed by `gcq_head`(), turning the supplied struct gcq * into struct gcq_head *. `gcq_q`() returns its struct gcq * argument and is used for type checking in `GCQ_ITEM`(). There are no functions for retrieving the raw q_prev and q_next pointers as these are usually clearer when used directly (if at all).

`gcq_remove`() returns the element removed and is always a valid operation after initialization. `gcq_onlist`() returns `false` if the structure links to itself and `true` otherwise. `gcq_empty`() is the negation of this operation performed on a head. `gcq_linked`() tests if `prev->q_next == next && next->q_prev == prev`.

`gcq_tie`() ties src after dst such that that if the old lists are DST, DST2 and SRC, SRC2, the new list is DST, SRC, SRC2, DST2. If dst and src are on the same list then any elements between but not including dst and src are cut from the list. If `dst == src` then the result is the same as `gcq_remove`(). `gcq_tie`() is equivalent to `gcq_tie_after`() except that the latter must only be used with arguments on separate lists or not on lists and asserts that `src != dst && dst->q_prev != src`. `gcq_tie_before`() performs the same operation on `dst->q_prev`.

`gcq_merge`() moves any elements on list src (but not src itself) to list dst. It is normally used with two heads via `gcq_merge_head`() or `gcq_merge_tail`(). If `GCQ_UNCONDITIONAL_MERGE` is defined prior to header inclusion then the merge operations will always perform a tie then remove src from the new list, which may reduce code size slightly.

`gcq_clear`() initializes all elements currently linked with q and is normally used with a head as `gcq_remove_all`().

`gcq_insert_after`() and `gcq_insert_before`() are slightly optimized versions of `gcq_tie`() for the case where off is not on a list and include assertions to this effect, which are also useful to detect missing initialization. `gcq_insert_head`() and `gcq_insert_tail`() are the same operations applied to a head.

`GCQ_GOT_FIRST`() and `GCQ_GOT_LAST`() set var to a pointer to the first or last struct gcq in the list or `NULL` if the list is empty and return `false` if empty and `true` otherwise. The boolean return is to emphasise that it is not normally safe and useful to directly pass the raw first/next/etc. pointer to another function. The macros are written such that the `NULL` values will be optimized out if not otherwise used. `DEQUEUED` variants also remove the member from the list. `COND` variants take an additional condition that is evaluated when the macro would otherwise return `true`. If the condition is false var or tvar is set to `NULL` and no dequeue is performed.

`GCQ_GOT_NEXT`() and variants take pointers to the current position, list head, and starting point as arguments. The list head will be skipped when it is reached unless it is equal to the starting point; upon reaching the starting point var will be set to `NULL` and the macro will return `false`. The next and prev macros also assert that current is on the list unless it is equal to start. These macros are the only provided method for iterating through the list from an arbitrary point. Traversal macros are only provided for list heads, however `gcq_head`() can be used to treat any item as a head.

Foreach variants contain an embedded `for` statement for iterating over a list. Those containing `REV` use the q_prev pointer for traversal, others use q_next. The plain `GCQ_FOREACH`() uses a single variable. `NVAR` variants save the next pointer at the top of the loop so that the current element can be removed without adjusting var. This is useful when var is passed to a function that might remove it but will not otherwise modify the list. When the head is reached both var and nvar elements are left pointing to the list head. `FOREACH` asserts that var, and `NVAR` asserts that nvar does not point to itself when starting the next loop. This assertion takes place after the variable is tested against the head so it is safe to remove all elements from the list. `RO` variants also set nvar but assert that the two variables are linked at the end of each iteration. This is useful when calling a function that is not supposed to remove the element passed. `DEQUEUED` variants are like `NVAR` but remove each element before the code block is executed. `TYPED` variants are equivalent to the untyped versions except that they take three extra arguments: a typed pointer, the type name, and the member name of the struct gcq used in this list. tvar is set to `NULL` when the head is reached.

`GCQ_FIND`() is a foreach loop that does nothing except break when the supplied condition is true. `REV` and `TYPED` variants are available.

# SEE ALSO

gcc(1), _DIAGASSERT(3), assert(3), queue(3), KASSERT(9)

# HISTORY

GCQ appeared in NetBSD 5.0.

May 1, 2007 | NetBSD 9.5