src/task.c

/*
 * Task management functions.
 *
 * Copyright 2000-2009 Willy Tarreau <w@1wt.eu>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 */

#include <string.h>

#include <common/config.h>
#include <common/memory.h>
#include <common/mini-clist.h>
#include <common/standard.h>
#include <common/time.h>
#include <eb32tree.h>

#include <proto/proxy.h>
#include <proto/stream.h>
#include <proto/task.h>

struct pool_head *pool2_task;

unsigned int nb_tasks = 0;
unsigned int tasks_run_queue = 0;
unsigned int tasks_run_queue_cur = 0;    /* copy of the run queue size */
unsigned int nb_tasks_cur = 0;     /* copy of the tasks count */
unsigned int niced_tasks = 0;      /* number of niced tasks in the run queue */


static struct eb_root timers;      /* sorted timers tree */
static struct eb_root rqueue;      /* tree constituting the run queue */
static unsigned int rqueue_ticks;  /* insertion count */

/* Puts the task <t> in run queue at a position depending on t->nice. <t> is
 * returned. The nice value assigns boosts in 32th of the run queue size. A
 * nice value of -1024 sets the task to -tasks_run_queue*32, while a nice value
 * of 1024 sets the task to tasks_run_queue*32. The state flags are cleared, so
 * the caller will have to set its flags after this call.
 * The task must not already be in the run queue. If unsure, use the safer
 * task_wakeup() function.
 */
struct task *__task_wakeup(struct task *t)
{
	tasks_run_queue++;
	t->rq.key = ++rqueue_ticks;

	if (likely(t->nice)) {
		int offset;

		niced_tasks++;
		if (likely(t->nice > 0))
			offset = (unsigned)((tasks_run_queue * (unsigned int)t->nice) / 32U);
		else
			offset = -(unsigned)((tasks_run_queue * (unsigned int)-t->nice) / 32U);
		t->rq.key += offset;
	}

	/* reset flag to pending ones
	 * Note: __task_wakeup must not be called
	 * if task is running
	 */
	t->state = t->pending_state;
	eb32_insert(&rqueue, &t->rq);
	return t;
}

/*
 * __task_queue()
 *
 * Inserts a task into the wait queue at the position given by its expiration
 * date. It does not matter if the task was already in the wait queue or not,
 * as it will be unlinked. The task must not have an infinite expiration timer.
 * Last, tasks must not be queued further than the end of the tree, which is
 * between <now_ms> and <now_ms> + 2^31 ms (now+24days in 32bit).
 *
 * This function should not be used directly, it is meant to be called by the
 * inline version of task_queue() which performs a few cheap preliminary tests
 * before deciding to call __task_queue().
 */
void __task_queue(struct task *task)
{
	if (likely(task_in_wq(task)))
		__task_unlink_wq(task);

	/* the task is not in the queue now */
	task->wq.key = task->expire;
#ifdef DEBUG_CHECK_INVALID_EXPIRATION_DATES
	if (tick_is_lt(task->wq.key, now_ms))
		/* we're queuing too far away or in the past (most likely) */
		return;
#endif

	eb32_insert(&timers, &task->wq);

	return;
}

/*
 * Extract all expired timers from the timer queue, and wakes up all
 * associated tasks. Returns the date of next event (or eternity).
 */
int wake_expired_tasks()
{
	struct task *task;
	struct eb32_node *eb;

	while (1) {
		eb = eb32_lookup_ge(&timers, now_ms - TIMER_LOOK_BACK);
		if (unlikely(!eb)) {
			/* we might have reached the end of the tree, typically because
			* <now_ms> is in the first half and we're first scanning the last
			* half. Let's loop back to the beginning of the tree now.
			*/
			eb = eb32_first(&timers);
			if (likely(!eb))
				break;
		}

		if (likely(tick_is_lt(now_ms, eb->key))) {
			/* timer not expired yet, revisit it later */
			return eb->key;
		}

		/* timer looks expired, detach it from the queue */
		task = eb32_entry(eb, struct task, wq);
		__task_unlink_wq(task);

		/* It is possible that this task was left at an earlier place in the
		 * tree because a recent call to task_queue() has not moved it. This
		 * happens when the new expiration date is later than the old one.
		 * Since it is very unlikely that we reach a timeout anyway, it's a
		 * lot cheaper to proceed like this because we almost never update
		 * the tree. We may also find disabled expiration dates there. Since
		 * we have detached the task from the tree, we simply call task_queue
		 * to take care of this. Note that we might occasionally requeue it at
		 * the same place, before <eb>, so we have to check if this happens,
		 * and adjust <eb>, otherwise we may skip it which is not what we want.
		 * We may also not requeue the task (and not point eb at it) if its
		 * expiration time is not set.
		 */
		if (!tick_is_expired(task->expire, now_ms)) {
			if (!tick_isset(task->expire))
				continue;
			__task_queue(task);
			continue;
		}
		task_wakeup(task, TASK_WOKEN_TIMER);
	}

	/* No task is expired */
	return TICK_ETERNITY;
}

/* The run queue is chronologically sorted in a tree. An insertion counter is
 * used to assign a position to each task. This counter may be combined with
 * other variables (eg: nice value) to set the final position in the tree. The
 * counter may wrap without a problem, of course. We then limit the number of
 * tasks processed at once to 1/4 of the number of tasks in the queue, and to
 * 200 max in any case, so that general latency remains low and so that task
 * positions have a chance to be considered.
 *
 * The function adjusts <next> if a new event is closer.
 */
void process_runnable_tasks()
{
	struct task *t;
	int i;
	int max_processed;
	struct eb32_node *rq_next;
	int rewind;
	struct task *local_tasks[16];
	int local_tasks_count;
	tasks_run_queue_cur = tasks_run_queue; /* keep a copy for reporting */
	nb_tasks_cur = nb_tasks;
	max_processed = tasks_run_queue;
	if (!tasks_run_queue)
		return;

	if (max_processed > 200)
		max_processed = 200;

	if (likely(niced_tasks))
		max_processed = (max_processed + 3) / 4;

	while (max_processed > 0) {
		/* Note: this loop is one of the fastest code path in
		 * the whole program. It should not be re-arranged
		 * without a good reason.
		 */

		rewind = 0;
		rq_next = eb32_lookup_ge(&rqueue, rqueue_ticks - TIMER_LOOK_BACK);
		if (!rq_next) {
			/* we might have reached the end of the tree, typically because
			 * <rqueue_ticks> is in the first half and we're first scanning
			 * the last half. Let's loop back to the beginning of the tree now.
			 */
			rq_next = eb32_first(&rqueue);
			if (!rq_next) {
				break;
			}
			rewind = 1;
		}

		local_tasks_count = 0;
		while (local_tasks_count < 16) {
			t = eb32_entry(rq_next, struct task, rq);
			rq_next = eb32_next(rq_next);
			/* detach the task from the queue */
			__task_unlink_rq(t);
			t->state |= TASK_RUNNING;
			t->pending_state = 0;
			t->calls++;
			local_tasks[local_tasks_count++] = t;
			if (!rq_next) {
				if (rewind || !(rq_next = eb32_first(&rqueue))) {
					break;
				}
				rewind = 1;
			}
		}

		if (!local_tasks_count)
			break;


		for (i = 0; i < local_tasks_count ; i++) {
			t = local_tasks[i];
			/* This is an optimisation to help the processor's branch
			 * predictor take this most common call.
			 */
			if (likely(t->process == process_stream))
				t = process_stream(t);
			else
				t = t->process(t);
			local_tasks[i] = t;
		}

		max_processed -= local_tasks_count;
		for (i = 0; i < local_tasks_count ; i++) {
			t = local_tasks[i];
			if (likely(t != NULL)) {
				t->state &= ~TASK_RUNNING;
				/* If there is a pending state
				 * we have to wake up the task
				 * immediatly, else we defer
				 * it into wait queue
				 */
				if (t->pending_state)
					__task_wakeup(t);
				else
					task_queue(t);
			}
		}
	}
}

/* perform minimal intializations, report 0 in case of error, 1 if OK. */
int init_task()
{
	memset(&timers, 0, sizeof(timers));
	memset(&rqueue, 0, sizeof(rqueue));
	pool2_task = create_pool("task", sizeof(struct task), MEM_F_SHARED);
	return pool2_task != NULL;
}

/*
 * Local variables:
 *  c-indent-level: 8
 *  c-basic-offset: 8
 * End:
 */