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QL, QR: Add documentation.

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David Goldblatt 2020-04-10 11:38:33 -07:00 committed by David Goldblatt
parent 79ae7f9211
commit 877af247a8
2 changed files with 162 additions and 10 deletions
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86
include/jemalloc/internal/ql.h
View File

@ -3,45 +3,85 @@
#include "jemalloc/internal/qr.h"
/*
* A linked-list implementation.
*
* This is built on top of the ring implementation, but that can be viewed as an
* implementation detail (i.e. trying to advance past the tail of the list
* doesn't wrap around).
*
* You define a struct like so:
* typedef strucy my_s my_t;
* struct my_s {
* int data;
* ql_elm(my_t) my_link;
* };
*
* // We wobble between "list" and "head" for this type; we're now mostly
* // heading towards "list".
* typedef ql_head(my_t) my_list_t;
*
* You then pass a my_list_t * for a_head arguments, a my_t * for a_elm
* arguments, the token "my_link" for a_field arguments, and the token "my_t"
* for a_type arguments.
*/
/* List definitions. */
#define ql_head(a_type) \
struct { \
a_type *qlh_first; \
}
/* Static initializer for an empty list. */
#define ql_head_initializer(a_head) {NULL}
/* The field definition. */
#define ql_elm(a_type) qr(a_type)
/* List functions. */
/* A pointer to the first element in the list, or NULL if the list is empty. */
#define ql_first(a_head) ((a_head)->qlh_first)
/* Dynamically initializes a list. */
#define ql_new(a_head) do { \
ql_first(a_head) = NULL; \
} while (0)
#define ql_clear(a_head) ql_new(a_head)
/*
* Sets dest to be the contents of src (overwriting any elements there), leaving
* src empty.
*/
#define ql_move(a_head_dest, a_head_src) do { \
ql_first(a_head_dest) = ql_first(a_head_src); \
ql_clear(a_head_src); \
ql_new(a_head_src); \
} while (0)
/* True if the list is empty, otherwise false. */
#define ql_empty(a_head) (ql_first(a_head) == NULL)
/*
* Initializes a ql_elm. Must be called even if the field is about to be
* overwritten.
*/
#define ql_elm_new(a_elm, a_field) qr_new((a_elm), a_field)
/*
* Obtains the last item in the list.
*/
#define ql_last(a_head, a_field) \
(ql_empty(a_head) ? NULL : qr_prev(ql_first(a_head), a_field))
/*
* Gets a pointer to the next/prev element in the list. Trying to advance past
* the end or retreat before the beginning of the list returns NULL.
*/
#define ql_next(a_head, a_elm, a_field) \
((ql_last(a_head, a_field) != (a_elm)) \
? qr_next((a_elm), a_field) : NULL)
#define ql_prev(a_head, a_elm, a_field) \
((ql_first(a_head) != (a_elm)) ? qr_prev((a_elm), a_field) \
: NULL)
/* Inserts a_elm before a_qlelm in the list. */
#define ql_before_insert(a_head, a_qlelm, a_elm, a_field) do { \
qr_before_insert((a_qlelm), (a_elm), a_field); \
if (ql_first(a_head) == (a_qlelm)) { \
@ -49,9 +89,11 @@ struct { \
} \
} while (0)
/* Inserts a_elm after a_qlelm in the list. */
#define ql_after_insert(a_qlelm, a_elm, a_field) \
qr_after_insert((a_qlelm), (a_elm), a_field)
/* Inserts a_elm as the first item in the list. */
#define ql_head_insert(a_head, a_elm, a_field) do { \
if (!ql_empty(a_head)) { \
qr_before_insert(ql_first(a_head), (a_elm), a_field); \
@ -59,6 +101,7 @@ struct { \
ql_first(a_head) = (a_elm); \
} while (0)
/* Inserts a_elm as the last item in the list. */
#define ql_tail_insert(a_head, a_elm, a_field) do { \
if (!ql_empty(a_head)) { \
qr_before_insert(ql_first(a_head), (a_elm), a_field); \
@ -66,16 +109,21 @@ struct { \
ql_first(a_head) = qr_next((a_elm), a_field); \
} while (0)
/*
* Given lists a = [a_1, ..., a_n] and [b_1, ..., b_n], results in:
* a = [a1, ..., a_n, b_1, ..., b_n] and b = [].
*/
#define ql_concat(a_head_a, a_head_b, a_field) do { \
if (ql_empty(a_head_a)) { \
ql_move(a_head_a, a_head_b); \
} else if (!ql_empty(a_head_b)) { \
qr_meld(ql_first(a_head_a), ql_first(a_head_b), \
a_field); \
ql_clear(a_head_b); \
ql_new(a_head_b); \
} \
} while (0)
/* Removes a_elm from the list. */
#define ql_remove(a_head, a_elm, a_field) do { \
if (ql_first(a_head) == (a_elm)) { \
ql_first(a_head) = qr_next(ql_first(a_head), a_field); \
@ -83,20 +131,29 @@ struct { \
if (ql_first(a_head) != (a_elm)) { \
qr_remove((a_elm), a_field); \
} else { \
ql_clear(a_head); \
ql_new(a_head); \
} \
} while (0)
/* Removes the first item in the list. */
#define ql_head_remove(a_head, a_type, a_field) do { \
a_type *t = ql_first(a_head); \
ql_remove((a_head), t, a_field); \
} while (0)
/* Removes the last item in the list. */
#define ql_tail_remove(a_head, a_type, a_field) do { \
a_type *t = ql_last(a_head, a_field); \
ql_remove((a_head), t, a_field); \
} while (0)
/*
* Given a = [a_1, a_2, ..., a_n-1, a_n, a_n+1, ...],
* ql_split(a, a_n, b, some_field) results in
* a = [a_1, a_2, ..., a_n-1]
* and replaces b's contents with:
* b = [a_n, a_n+1, ...]
*/
#define ql_split(a_head_a, a_elm, a_head_b, a_field) do { \
if (ql_first(a_head_a) == (a_elm)) { \
ql_move(a_head_b, a_head_a); \
@ -116,6 +173,21 @@ struct { \
ql_first(a_head) = qr_next(ql_first(a_head), a_field); \
} while (0)
/*
* Helper macro to iterate over each element in a list in order, starting from
* the head (or in reverse order, starting from the tail). The usage is
* (assuming my_t and my_list_t defined as above).
*
* int sum(my_list_t *list) {
* int sum = 0;
* my_t *iter;
* ql_foreach(iter, list, link) {
* sum += iter->data;
* }
* return sum;
* }
*/
#define ql_foreach(a_var, a_head, a_field) \
qr_foreach((a_var), ql_first(a_head), a_field)

86
include/jemalloc/internal/qr.h
View File

@ -1,6 +1,21 @@
#ifndef JEMALLOC_INTERNAL_QR_H
#define JEMALLOC_INTERNAL_QR_H
/*
* A ring implementation based on an embedded circular doubly-linked list.
*
* You define your struct like so:
*
* typedef struct my_s my_t;
* struct my_s {
* int data;
* qr(my_t) my_link;
* };
*
* And then pass a my_t * into macros for a_qr arguments, and the token
* "my_link" into a_field fields.
*/
/* Ring definitions. */
#define qr(a_type) \
struct { \
@ -8,17 +23,41 @@ struct { \
a_type *qre_prev; \
}
/* Ring functions. */
/*
* Initialize a qr link. Every link must be initialized before being used, even
* if that initialization is going to be immediately overwritten (say, by being
* passed into an insertion macro).
*/
#define qr_new(a_qr, a_field) do { \
(a_qr)->a_field.qre_next = (a_qr); \
(a_qr)->a_field.qre_prev = (a_qr); \
} while (0)
/*
* Go forwards or backwards in the ring. Note that (the ring being circular), this
* always succeeds -- you just keep looping around and around the ring if you
* chase pointers without end.
*/
#define qr_next(a_qr, a_field) ((a_qr)->a_field.qre_next)
#define qr_prev(a_qr, a_field) ((a_qr)->a_field.qre_prev)
/* a_qr_a can directly be a qr_next() macro, but a_qr_b cannot. */
/*
* Given two rings:
* a -> a_1 -> ... -> a_n --
* ^ |
* |------------------------
*
* b -> b_1 -> ... -> b_n --
* ^ |
* |------------------------
*
* Results in the ring:
* a -> a_1 -> ... -> a_n -> b -> b_1 -> ... -> b_n --
* ^ |
* |-------------------------------------------------|
*
* a_qr_a can directly be a qr_next() macro, but a_qr_b cannot.
*/
#define qr_meld(a_qr_a, a_qr_b, a_field) do { \
(a_qr_b)->a_field.qre_prev->a_field.qre_next = \
(a_qr_a)->a_field.qre_prev; \
@ -29,28 +68,69 @@ struct { \
(a_qr_b)->a_field.qre_prev->a_field.qre_next = (a_qr_b); \
} while (0)
/*
* Logically, this is just a meld. The intent, though, is that a_qrelm is a
* single-element ring, so that "before" has a more obvious interpretation than
* meld.
*/
#define qr_before_insert(a_qrelm, a_qr, a_field) \
qr_meld((a_qrelm), (a_qr), a_field)
/* Ditto, but inserting after rather than before. */
#define qr_after_insert(a_qrelm, a_qr, a_field) \
qr_before_insert(qr_next(a_qrelm, a_field), (a_qr), a_field)
/*
* Inverts meld; given the ring:
* a -> a_1 -> ... -> a_n -> b -> b_1 -> ... -> b_n --
* ^ |
* |-------------------------------------------------|
*
* Results in two rings:
* a -> a_1 -> ... -> a_n --
* ^ |
* |------------------------
*
* b -> b_1 -> ... -> b_n --
* ^ |
* |------------------------
*
* qr_meld() and qr_split() are functionally equivalent, so there's no need to
* have two copies of the code.
*/
#define qr_split(a_qr_a, a_qr_b, a_field) \
qr_meld((a_qr_a), (a_qr_b), a_field)
/*
* Splits off a_qr from the rest of its ring, so that it becomes a
* single-element ring.
*/
#define qr_remove(a_qr, a_field) \
qr_split(qr_next(a_qr, a_field), (a_qr), a_field)
/*
* Helper macro to iterate over each element in a ring exactly once, starting
* with a_qr. The usage is (assuming my_t defined as above):
*
* int sum(my_t *item) {
* int sum = 0;
* my_t *iter;
* qr_foreach(iter, item, link) {
* sum += iter->data;
* }
* return sum;
* }
*/
#define qr_foreach(var, a_qr, a_field) \
for ((var) = (a_qr); \
(var) != NULL; \
(var) = (((var)->a_field.qre_next != (a_qr)) \
? (var)->a_field.qre_next : NULL))
/*
* The same (and with the same usage) as qr_foreach, but in the opposite order,
* ending with a_qr.
*/
#define qr_reverse_foreach(var, a_qr, a_field) \
for ((var) = ((a_qr) != NULL) ? qr_prev(a_qr, a_field) : NULL; \
(var) != NULL; \