[paraslash.git] / sched.c

/*
 * Copyright (C) 2006-2013 Andre Noll <maan@systemlinux.org>
 *
 * Licensed under the GPL v2. For licencing details see COPYING.
 */

/** \file sched.c Paraslash's scheduling functions. */

#include <regex.h>
#include <assert.h>

#include "para.h"
#include "ipc.h"
#include "fd.h"
#include "list.h"
#include "sched.h"
#include "string.h"
#include "time.h"
#include "error.h"

static struct timeval now_struct;
struct timeval *now = &now_struct;

/*
 * Remove a task from the scheduler.
 *
 * \param t The task to remove.
 *
 * If the pre_select pointer of \a t is not \p NULL, it is removed from
 * the pre_select list of the scheduler. Same goes for \a post_select.
 */
static void unregister_task(struct task *t)
{
        assert(t->error < 0);
        PARA_INFO_LOG("unregistering %s (%s)\n", t->status,
                para_strerror(-t->error));
        if (t->pre_select)
                list_del(&t->pre_select_node);
        if (t->new_post_select || t->post_select)
                list_del(&t->post_select_node);
}

static inline bool timeout_is_zero(struct sched *s)
{
        struct timeval *tv = &s->select_timeout;
        return tv->tv_sec == 0 && tv->tv_usec == 0;
}

static void sched_preselect(struct sched *s)
{
        struct task *t, *tmp;

        list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
                if (t->notification != 0)
                        sched_min_delay(s);
                if (t->pre_select)
                        t->pre_select(s, t);
        }
}

//#define SCHED_DEBUG 1
static inline void call_post_select(struct sched *s, struct task *t)
{
#ifndef SCHED_DEBUG
        if (t->new_post_select) {
                t->error = t->new_post_select(s, t);
                return;
        }
        return t->post_select(s, t);
#else
        struct timeval t1, t2, diff;
        unsigned long pst;

        clock_get_realtime(&t1);
        if (t->new_post_select)
                t->error = t->new_post_select(s, t);
        else
                t->post_select(s, t);
        clock_get_realtime(&t2);
        tv_diff(&t1, &t2, &diff);
        pst = tv2ms(&diff);
        if (pst > 50)
                PARA_WARNING_LOG("%s: post_select time: %lums\n",
                        t->status, pst);
#endif
}

static void sched_post_select(struct sched *s)
{
        struct task *t, *tmp;

        list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
                if (t->error >= 0)
                        call_post_select(s, t);
//              PARA_INFO_LOG("%s: %d\n", t->status, t->ret);
                t->notification = 0;
                if (t->error >= 0)
                        continue;
                unregister_task(t);
        }
}

/**
 * The core function for all paraslash programs.
 *
 * \param s Pointer to the scheduler struct.
 *
 * This function updates the global \a now pointer, calls all registered
 * pre_select hooks which may set the timeout and add any file descriptors to
 * the fd sets of \a s.  Next, it calls para_select() and makes the result available
 * to the registered tasks by calling their post_select hook.
 *
 * \return Zero if no more tasks are left in either of the two lists, negative
 * if para_select returned an error.
 *
 * \sa task, now.
 */
int schedule(struct sched *s)
{
        int ret;

        if (!s->select_function)
                s->select_function = para_select;
again:
        FD_ZERO(&s->rfds);
        FD_ZERO(&s->wfds);
        s->select_timeout = s->default_timeout;
        s->max_fileno = -1;
        clock_get_realtime(now);
        sched_preselect(s);
        ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
                &s->select_timeout);
        if (ret < 0)
                return ret;
        if (ret == 0) {
                /*
                 * APUE: Be careful not to check the descriptor sets on return
                 * unless the return value is greater than zero. The return
                 * state of the descriptor sets is implementation dependent if
                 * either a signal is caught or the timer expires.
                 */
                FD_ZERO(&s->rfds);
                FD_ZERO(&s->wfds);
        }
        clock_get_realtime(now);
        sched_post_select(s);
        if (list_empty(&s->pre_select_list) && list_empty(&s->post_select_list))
                return 0;
        goto again;
}

/**
 * Add a task to the scheduler.
 *
 * \param t The task to add.
 * \param s The scheduler instance to add the task to.
 *
 * If the pre_select pointer of \a t is not \p NULL, it is added to
 * the pre_select list of the scheduler. Same goes for post_select.
 *
 * \sa task::pre_select, task::post_select
 */
void register_task(struct sched *s, struct task *t)
{
        PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
        t->notification = 0;
        if (!s->pre_select_list.next)
                INIT_LIST_HEAD(&s->pre_select_list);
        if (!s->post_select_list.next)
                INIT_LIST_HEAD(&s->post_select_list);
        if (t->pre_select) {
                PARA_DEBUG_LOG("pre_select: %p\n", &t->pre_select);
                list_add_tail(&t->pre_select_node, &s->pre_select_list);
        }
        if (t->new_post_select) {
                PARA_DEBUG_LOG("post_select: %p\n", &t->new_post_select);
                list_add_tail(&t->post_select_node, &s->post_select_list);
        } else if ((t->post_select)) {
                PARA_DEBUG_LOG("post_select: %p\n", &t->post_select);
                list_add_tail(&t->post_select_node, &s->post_select_list);
        }
}

/**
 * Get the list of all registered tasks.
 *
 * \param s The scheduler instance to get the task list from.
 *
 * \return The task list.
 *
 * Each entry of the list contains an identifier which is simply a hex number.
 * The result is dynamically allocated and must be freed by the caller.
 */
char *get_task_list(struct sched *s)
{
        struct task *t, *tmp;
        char *msg = NULL;

        list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
                char *tmp_msg;
                tmp_msg = make_message("%s%p\tpre\t%s\n", msg? msg : "", t, t->status);
                free(msg);
                msg = tmp_msg;
        }
        list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
                char *tmp_msg;
//              if (t->pre_select)
//                      continue;
                tmp_msg = make_message("%s%p\tpost\t%s\n", msg? msg : "", t, t->status);
                free(msg);
                msg = tmp_msg;
        }
        //PARA_DEBUG_LOG("task list:\n%s", msg);
        return msg;
}

/**
 * Set the notification value of a task.
 *
 * \param t The task to notify.
 * \param err A positive error code.
 *
 * Tasks which honor notifications are supposed to call \ref
 * task_get_notification() in their post_select function and act on the
 * returned notification value.
 *
 * If the scheduler detects during its pre_select loop that at least one task
 * has been notified, the loop terminates, and the post_select methods of all
 * taks are immediately called again.
 *
 * The notification for a task is reset after the call to its post_select
 * method.
 *
 * \sa \ref task_get_notification().
 */
void task_notify(struct task *t, int err)
{
        assert(err > 0);
        if (t->notification == -err) /* ignore subsequent notifications */
                return;
        PARA_INFO_LOG("notifying task %s: %s\n", t->status, para_strerror(err));
        t->notification = -err;
}

/**
 * Return the notification value of a task.
 *
 * \param t The task to get the notification value from.
 *
 * \return The notification value. If this is negative, the task has been
 * notified by another task. Tasks are supposed to check for notifications by
 * calling this function from their post_select method.
 *
 * \sa \ref task_notify().
 */
int task_get_notification(struct task *t)
{
        return t->notification;
}

/**
 * Set the notification value of all tasks of a scheduler instance.
 *
 * \param s The scheduler instance whose tasks should be notified.
 * \param err A positive error code.
 *
 * This simply iterates over all existing tasks of \a s and sets each
 * task's notification value to \p -err.
 */
void task_notify_all(struct sched *s, int err)
{
        struct task *t;

        list_for_each_entry(t, &s->pre_select_list, pre_select_node)
                task_notify(t, err);
        list_for_each_entry(t, &s->post_select_list, post_select_node)
                task_notify(t, err);
}

/**
 * Set the select timeout to the minimal possible value.
 *
 * \param s Pointer to the scheduler struct.
 *
 * This causes the next select() call to return immediately.
 */
void sched_min_delay(struct sched *s)
{
        s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
}

/**
 * Impose an upper bound for the timeout of the next select() call.
 *
 * \param to Maximal allowed timeout.
 * \param s Pointer to the scheduler struct.
 *
 * If the current scheduler timeout is already smaller than \a to, this
 * function does nothing. Otherwise the timeout for the next select() call is
 * set to the given value.
 *
 * \sa sched_request_timeout_ms().
 */
void sched_request_timeout(struct timeval *to, struct sched *s)
{
        if (tv_diff(&s->select_timeout, to, NULL) > 0)
                s->select_timeout = *to;
}

/**
 * Force the next select() call to return before the given amount of milliseconds.
 *
 * \param ms The maximal allowed timeout in milliseconds.
 * \param s Pointer to the scheduler struct.
 *
 * Like sched_request_timeout() this imposes an upper bound on the timeout
 * value for the next select() call.
 */
void sched_request_timeout_ms(long unsigned ms, struct sched *s)
{
        struct timeval tv;
        ms2tv(ms, &tv);
        sched_request_timeout(&tv, s);
}

/**
 * Force the next select() call to return before the given future time.
 *
 * \param barrier Absolute time before select() should return.
 * \param s Pointer to the scheduler struct.
 *
 * \return If \a barrier is in the past, this function does nothing and returns
 * zero. Otherwise it returns one.
 *
 * \sa sched_request_barrier_or_min_delay().
 */
int sched_request_barrier(struct timeval *barrier, struct sched *s)
{
        struct timeval diff;

        if (tv_diff(now, barrier, &diff) > 0)
                return 0;
        sched_request_timeout(&diff, s);
        return 1;
}

/**
 * Force the next select() call to return before the given time.
 *
 * \param barrier Absolute time before select() should return.
 * \param s Pointer to the scheduler struct.
 *
 * \return If \a barrier is in the past, this function requests a minimal
 * timeout and returns zero. Otherwise it returns one.
 *
 * \sa sched_min_delay(), sched_request_barrier().
 */
int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
{
        struct timeval diff;

        if (tv_diff(now, barrier, &diff) > 0) {
                sched_min_delay(s);
                return 0;
        }
        sched_request_timeout(&diff, s);
        return 1;
}