/*
* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* See the COPYRIGHT file distributed with this work for additional
* information regarding copyright ownership.
*/
/*
* This is a generic implementation of a two-lock concurrent queue.
* There are built-in mutex locks for the head and tail of the queue,
* allowing elements to be safely added and removed at the same time.
*
* NULL is "end of list"
* -1 is "not linked"
*/
#ifndef ISC_QUEUE_H
#define ISC_QUEUE_H 1
#include <isc/assertions.h>
#include <isc/boolean.h>
#include <isc/mutex.h>
#ifdef ISC_QUEUE_CHECKINIT
#define ISC_QLINK_INSIST(x) ISC_INSIST(x)
#else
#define ISC_QLINK_INSIST(x) (void)0
#endif
#define ISC_QLINK(type) struct { type *prev, *next; }
#define ISC_QLINK_INIT(elt, link) \
do { \
(elt)->link.next = (elt)->link.prev = (void *)(-1); \
} while(0)
#define ISC_QLINK_LINKED(elt, link) ((void*)(elt)->link.next != (void*)(-1))
#define ISC_QUEUE(type) struct { \
type *head, *tail; \
isc_mutex_t headlock, taillock; \
}
#define ISC_QUEUE_INIT(queue, link) \
do { \
(void) isc_mutex_init(&(queue).taillock); \
(void) isc_mutex_init(&(queue).headlock); \
(queue).tail = (queue).head = NULL; \
} while (0)
#define ISC_QUEUE_EMPTY(queue) ISC_TF((queue).head == NULL)
#define ISC_QUEUE_DESTROY(queue) \
do { \
ISC_QLINK_INSIST(ISC_QUEUE_EMPTY(queue)); \
(void) isc_mutex_destroy(&(queue).taillock); \
(void) isc_mutex_destroy(&(queue).headlock); \
} while (0)
/*
* queues are meant to separate the locks at either end. For best effect, that
* means keeping the ends separate - i.e. non-empty queues work best.
*
* a push to an empty queue has to take the pop lock to update
* the pop side of the queue.
* Popping the last entry has to take the push lock to update
* the push side of the queue.
*
* The order is (pop, push), because a pop is presumably in the
* latency path and a push is when we're done.
*
* We do an MT hot test in push to see if we need both locks, so we can
* acquire them in order. Hopefully that makes the case where we get
* the push lock and find we need the pop lock (and have to release it) rare.
*
* > 1 entry - no collision, push works on one end, pop on the other
* 0 entry - headlock race
* pop wins - return(NULL), push adds new as both head/tail
* push wins - updates head/tail, becomes 1 entry case.
* 1 entry - taillock race
* pop wins - return(pop) sets head/tail NULL, becomes 0 entry case
* push wins - updates {head,tail}->link.next, pop updates head
* with new ->link.next and doesn't update tail
*
*/
#define ISC_QUEUE_PUSH(queue, elt, link) \
do { \
isc_boolean_t headlocked = ISC_FALSE; \
ISC_QLINK_INSIST(!ISC_QLINK_LINKED(elt, link)); \
if ((queue).head == NULL) { \
LOCK(&(queue).headlock); \
headlocked = ISC_TRUE; \
} \
LOCK(&(queue).taillock); \
if ((queue).tail == NULL && !headlocked) { \
UNLOCK(&(queue).taillock); \
LOCK(&(queue).headlock); \
LOCK(&(queue).taillock); \
headlocked = ISC_TRUE; \
} \
(elt)->link.prev = (queue).tail; \
(elt)->link.next = NULL; \
if ((queue).tail != NULL) \
(queue).tail->link.next = (elt); \
(queue).tail = (elt); \
UNLOCK(&(queue).taillock); \
if (headlocked) { \
if ((queue).head == NULL) \
(queue).head = (elt); \
UNLOCK(&(queue).headlock); \
} \
} while (0)
#define ISC_QUEUE_POP(queue, link, ret) \
do { \
LOCK(&(queue).headlock); \
ret = (queue).head; \
while (ret != NULL) { \
if (ret->link.next == NULL) { \
LOCK(&(queue).taillock); \
if (ret->link.next == NULL) { \
(queue).head = (queue).tail = NULL; \
UNLOCK(&(queue).taillock); \
break; \
}\
UNLOCK(&(queue).taillock); \
} \
(queue).head = ret->link.next; \
(queue).head->link.prev = NULL; \
break; \
} \
UNLOCK(&(queue).headlock); \
if (ret != NULL) \
(ret)->link.next = (ret)->link.prev = (void *)(-1); \
} while(0)
#define ISC_QUEUE_UNLINK(queue, elt, link) \
do { \
ISC_QLINK_INSIST(ISC_QLINK_LINKED(elt, link)); \
LOCK(&(queue).headlock); \
LOCK(&(queue).taillock); \
if ((elt)->link.prev == NULL) \
(queue).head = (elt)->link.next; \
else \
(elt)->link.prev->link.next = (elt)->link.next; \
if ((elt)->link.next == NULL) \
(queue).tail = (elt)->link.prev; \
else \
(elt)->link.next->link.prev = (elt)->link.prev; \
UNLOCK(&(queue).taillock); \
UNLOCK(&(queue).headlock); \
(elt)->link.next = (elt)->link.prev = (void *)(-1); \
} while(0)
#endif /* ISC_QUEUE_H */