mirror of https://gerrit.osmocom.org/libosmocore
timer: add scalable RB-tree based timer infrastructure
This patch adds RB-tree based timers which scales better than the previous list-based implementation. It does not require any API changes. It breaks ABI because the osmo_timer_list structure has changed though (to avoid this in the future, we can put internal data in some private structure). The following table summarizes the worst-case computational complexity of this new implementation versus the previous one: rb-tree list-based ------- ---------- calculate next timer to expire O(1) O(n) insertion of new timer O(log n) O(n) deletion of timer O(log n) O(1) timer-fired scheduler O(log n) O(3n) The most repeated cases are: * the calculation of the next timer to expire, that happens in every loop of our select function. * the timer-fired scheduler execution. This new implementation only loses in the deletion of timer scenario, this happens because we may need to rebalance the tree after the removal. So I think there is some real gain if we have some situation in which we have to handle lots of timers.
This commit is contained in:
parent
f74db0b33d
commit
066c912fd3
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@ -32,6 +32,7 @@
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#include <sys/time.h>
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#include <osmocom/core/linuxlist.h>
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#include <osmocom/core/linuxrbtree.h>
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/**
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* Timer management:
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@ -51,11 +52,10 @@
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*/
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/*! \brief A structure representing a single instance of a timer */
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struct osmo_timer_list {
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struct llist_head entry; /*!< \brief linked list header */
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struct rb_node node; /*!< \brief rb-tree node header */
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struct llist_head list; /*!< \brief internal list header */
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struct timeval timeout; /*!< \brief expiration time */
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unsigned int active : 1; /*!< \brief is it active? */
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unsigned int handled : 1; /*!< \brief did we already handle it */
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unsigned int in_list : 1; /*!< \brief is it in the global list? */
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void (*cb)(void*); /*!< \brief call-back called at timeout */
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void *data; /*!< \brief user data for callback */
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174
src/timer.c
174
src/timer.c
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@ -1,7 +1,12 @@
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/*
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* (C) 2008,2009 by Holger Hans Peter Freyther <zecke@selfish.org>
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* (C) 2011 by Harald Welte <laforge@gnumonks.org>
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* All Rights Reserved
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*
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* Authors: Holger Hans Peter Freyther <zecke@selfish.org>
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* Harald Welte <laforge@gnumonks.org>
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* Pablo Neira Ayuso <pablo@gnumonks.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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@ -18,6 +23,10 @@
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*
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*/
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/* These store the amount of time that we wait until next timer expires. */
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static struct timeval nearest;
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static struct timeval *nearest_p;
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/*! \addtogroup timer
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* @{
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*/
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@ -27,35 +36,41 @@
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#include <assert.h>
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#include <string.h>
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#include <limits.h>
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#include <osmocom/core/timer.h>
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#include <osmocom/core/linuxlist.h>
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static LLIST_HEAD(timer_list);
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static struct timeval s_nearest_time;
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static struct timeval s_select_time;
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static struct rb_root timer_root = RB_ROOT;
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#define MICRO_SECONDS 1000000LL
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static void __add_timer(struct osmo_timer_list *timer)
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{
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struct rb_node **new = &(timer_root.rb_node);
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struct rb_node *parent = NULL;
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#define TIME_SMALLER(left, right) \
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(left.tv_sec*MICRO_SECONDS+left.tv_usec) <= (right.tv_sec*MICRO_SECONDS+right.tv_usec)
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while (*new) {
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struct osmo_timer_list *this;
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this = container_of(*new, struct osmo_timer_list, node);
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parent = *new;
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if (timercmp(&timer->timeout, &this->timeout, <))
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new = &((*new)->rb_left);
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else
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new = &((*new)->rb_right);
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}
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rb_link_node(&timer->node, parent, new);
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rb_insert_color(&timer->node, &timer_root);
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}
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/*! \brief add a new timer to the timer management
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* \param[in] timer the timer that should be added
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*/
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void osmo_timer_add(struct osmo_timer_list *timer)
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{
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struct osmo_timer_list *list_timer;
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/* TODO: Optimize and remember the closest item... */
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timer->active = 1;
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/* this might be called from within update_timers */
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llist_for_each_entry(list_timer, &timer_list, entry)
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if (timer == list_timer)
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return;
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timer->in_list = 1;
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llist_add(&timer->entry, &timer_list);
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INIT_LLIST_HEAD(&timer->list);
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__add_timer(timer);
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}
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/*! \brief schedule a timer at a given future relative time
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@ -74,10 +89,9 @@ osmo_timer_schedule(struct osmo_timer_list *timer, int seconds, int microseconds
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struct timeval current_time;
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gettimeofday(¤t_time, NULL);
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unsigned long long currentTime = current_time.tv_sec * MICRO_SECONDS + current_time.tv_usec;
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currentTime += seconds * MICRO_SECONDS + microseconds;
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timer->timeout.tv_sec = currentTime / MICRO_SECONDS;
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timer->timeout.tv_usec = currentTime % MICRO_SECONDS;
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timer->timeout.tv_sec = seconds;
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timer->timeout.tv_usec = microseconds;
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timeradd(&timer->timeout, ¤t_time, &timer->timeout);
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osmo_timer_add(timer);
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}
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@ -89,10 +103,12 @@ osmo_timer_schedule(struct osmo_timer_list *timer, int seconds, int microseconds
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*/
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void osmo_timer_del(struct osmo_timer_list *timer)
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{
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if (timer->in_list) {
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if (timer->active) {
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timer->active = 0;
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timer->in_list = 0;
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llist_del(&timer->entry);
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rb_erase(&timer->node, &timer_root);
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/* make sure this is not already scheduled for removal. */
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if (!llist_empty(&timer->list))
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llist_del_init(&timer->list);
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}
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}
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@ -116,26 +132,28 @@ int osmo_timer_pending(struct osmo_timer_list *timer)
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*/
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struct timeval *osmo_timers_nearest(void)
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{
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struct timeval current_time;
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static struct timeval no_timers = { 0, 0 };
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if (s_nearest_time.tv_sec == 0 && s_nearest_time.tv_usec == 0)
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return NULL;
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if (nearest_p != NULL && !timerisset(nearest_p))
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return nearest_p;
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else
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return &no_timers;
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}
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if (gettimeofday(¤t_time, NULL) == -1)
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return NULL;
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unsigned long long nearestTime = s_nearest_time.tv_sec * MICRO_SECONDS + s_nearest_time.tv_usec;
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unsigned long long currentTime = current_time.tv_sec * MICRO_SECONDS + current_time.tv_usec;
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if (nearestTime < currentTime) {
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s_select_time.tv_sec = 0;
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s_select_time.tv_usec = 0;
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} else {
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s_select_time.tv_sec = (nearestTime - currentTime) / MICRO_SECONDS;
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s_select_time.tv_usec = (nearestTime - currentTime) % MICRO_SECONDS;
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static void update_nearest(struct timeval *cand, struct timeval *current)
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{
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if (cand->tv_sec != LONG_MAX) {
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if (timercmp(cand, current, >))
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timersub(cand, current, &nearest);
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else {
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/* loop again inmediately */
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nearest.tv_sec = 0;
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nearest.tv_usec = 0;
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}
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nearest_p = &nearest;
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} else {
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nearest_p = NULL;
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}
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return &s_select_time;
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}
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/*
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*/
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void osmo_timers_prepare(void)
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{
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struct osmo_timer_list *timer, *nearest_timer = NULL;
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llist_for_each_entry(timer, &timer_list, entry) {
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if (!nearest_timer || TIME_SMALLER(timer->timeout, nearest_timer->timeout)) {
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nearest_timer = timer;
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}
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}
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struct rb_node *node;
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struct timeval current;
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if (nearest_timer) {
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s_nearest_time = nearest_timer->timeout;
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gettimeofday(¤t, NULL);
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node = rb_first(&timer_root);
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if (node) {
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struct osmo_timer_list *this;
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this = container_of(node, struct osmo_timer_list, node);
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update_nearest(&this->timeout, ¤t);
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} else {
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memset(&s_nearest_time, 0, sizeof(struct timeval));
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nearest_p = NULL;
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}
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}
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int osmo_timers_update(void)
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{
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struct timeval current_time;
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struct osmo_timer_list *timer, *tmp;
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struct rb_node *node;
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struct llist_head timer_eviction_list;
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struct osmo_timer_list *this;
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int work = 0;
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gettimeofday(¤t_time, NULL);
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INIT_LLIST_HEAD(&timer_eviction_list);
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for (node = rb_first(&timer_root); node; node = rb_next(node)) {
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this = container_of(node, struct osmo_timer_list, node);
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if (timercmp(&this->timeout, ¤t_time, >))
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break;
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llist_add(&this->list, &timer_eviction_list);
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}
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/*
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* The callbacks might mess with our list and in this case
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* even llist_for_each_entry_safe is not safe to use. To allow
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* del_timer, add_timer, schedule_timer to be called from within
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* the callback we jump through some loops.
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* osmo_timer_del to be called from within the callback we need
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* to restart the iteration for each element scheduled for removal.
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*
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* First we set the handled flag of each active timer to zero,
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* then we iterate over the list and execute the callbacks. As the
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* list might have been changed (specially the next) from within
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* the callback we have to start over again. Once every callback
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* is dispatched we will remove the non-active from the list.
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*
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* TODO: If this is a performance issue we can poison a global
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* variable in add_timer and del_timer and only then restart.
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* The problematic scenario is the following: Given two timers A
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* and B that have expired at the same time. Thus, they are both
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* in the eviction list in this order: A, then B. If we remove
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* timer B from the A's callback, we continue with B in the next
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* iteration step, leading to an access-after-release.
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*/
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llist_for_each_entry(timer, &timer_list, entry) {
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timer->handled = 0;
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}
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restart:
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llist_for_each_entry(timer, &timer_list, entry) {
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if (!timer->handled && TIME_SMALLER(timer->timeout, current_time)) {
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timer->handled = 1;
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timer->active = 0;
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(*timer->cb)(timer->data);
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llist_for_each_entry(this, &timer_eviction_list, list) {
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osmo_timer_del(this);
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this->cb(this->data);
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work = 1;
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goto restart;
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}
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}
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llist_for_each_entry_safe(timer, tmp, &timer_list, entry) {
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timer->handled = 0;
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if (!timer->active) {
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osmo_timer_del(timer);
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}
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}
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return work;
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}
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int osmo_timers_check(void)
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{
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struct osmo_timer_list *timer;
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struct rb_node *node;
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int i = 0;
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llist_for_each_entry(timer, &timer_list, entry) {
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for (node = rb_first(&timer_root); node; node = rb_next(node)) {
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i++;
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}
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return i;
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