/*
- * Copyright (C) 2006-2014 Andre Noll <maan@systemlinux.org>
+ * Copyright (C) 2006 Andre Noll <maan@tuebingen.mpg.de>
*
* 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 "time.h"
#include "error.h"
-static struct timeval now_struct;
-struct timeval *now = &now_struct;
+/**
+ * The possible states of a task.
+ *
+ * In addition to the states listed here, a task may also enter zombie state.
+ * This happens when its ->post_select function returns negative, the ->status
+ * field is then set to this return value. Such tasks are not scheduled any
+ * more (i.e. ->pre_select() and ->post_select() are no longer called), but
+ * they stay on the scheduler task list until \ref task_reap() or
+ * \ref sched_shutdown() is called.
+ */
+enum task_status {
+ /** Task has been reaped and may be removed from the task list. */
+ TS_DEAD,
+ /** Task is active. */
+ TS_RUNNING,
+};
-static inline bool timeout_is_zero(struct sched *s)
-{
- struct timeval *tv = &s->select_timeout;
- return tv->tv_sec == 0 && tv->tv_usec == 0;
-}
+struct task {
+ /** A copy of the task name supplied when the task was registered. */
+ char *name;
+ /** Copied during task_register(). */
+ struct task_info info;
+ /* TS_RUNNING, TS_DEAD, or zombie (negative value). */
+ int status;
+ /** Position of the task in the task list of the scheduler. */
+ struct list_head node;
+ /** If less than zero, the task was notified by another task. */
+ int notification;
+};
+
+static struct timeval now_struct;
+const struct timeval *now = &now_struct;
static void sched_preselect(struct sched *s)
{
struct task *t, *tmp;
list_for_each_entry_safe(t, tmp, &s->task_list, node) {
- if (t->error < 0)
+ if (t->status < 0)
continue;
if (t->notification != 0)
sched_min_delay(s);
- if (t->pre_select)
- t->pre_select(s, t);
+ if (t->info.pre_select)
+ t->info.pre_select(s, t->info.context);
}
}
+static void unlink_and_free_task(struct task *t)
+{
+ PARA_INFO_LOG("freeing task %s\n", t->name);
+ list_del(&t->node);
+ free(t->name);
+ free(t);
+}
+
//#define SCHED_DEBUG 1
static inline void call_post_select(struct sched *s, struct task *t)
{
+ int ret;
+
#ifndef SCHED_DEBUG
- t->error = t->post_select(s, t);
+ ret = t->info.post_select(s, t->info.context);
#else
struct timeval t1, t2, diff;
unsigned long pst;
clock_get_realtime(&t1);
- t->error = t->post_select(s, t);
+ ret = t->info.post_select(s, t->info.context);
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);
+ t->name, pst);
#endif
+ t->status = ret < 0? ret : TS_RUNNING;
}
-static void sched_post_select(struct sched *s)
+static unsigned sched_post_select(struct sched *s)
{
struct task *t, *tmp;
+ unsigned num_running_tasks = 0;
list_for_each_entry_safe(t, tmp, &s->task_list, node) {
- call_post_select(s, t);
- t->notification = 0;
- if (t->error < 0)
- list_del(&t->node);
+ if (t->status == TS_DEAD) /* task has been reaped */
+ unlink_and_free_task(t);
+ else if (t->status == TS_RUNNING) {
+ call_post_select(s, t); /* sets t->status */
+ t->notification = 0;
+ if (t->status == TS_RUNNING)
+ num_running_tasks++;
+ }
}
+ return num_running_tasks;
}
/**
* \return Zero if no more tasks are left in the task list, negative if the
* select function returned an error.
*
- * \sa \ref task, \ref now.
+ * \sa \ref now.
*/
int schedule(struct sched *s)
{
int ret;
+ unsigned num_running_tasks;
if (!s->select_function)
s->select_function = para_select;
FD_ZERO(&s->wfds);
s->select_timeout = s->default_timeout;
s->max_fileno = -1;
- clock_get_realtime(now);
+ clock_get_realtime(&now_struct);
sched_preselect(s);
ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
&s->select_timeout);
FD_ZERO(&s->rfds);
FD_ZERO(&s->wfds);
}
- clock_get_realtime(now);
- sched_post_select(s);
- if (list_empty(&s->task_list))
+ clock_get_realtime(&now_struct);
+ num_running_tasks = sched_post_select(s);
+ if (num_running_tasks == 0)
return 0;
goto again;
}
/**
- * Add a task to the scheduler.
+ * Obtain the error status of a task and deallocate its resources.
+ *
+ * \param tptr Identifies the task to reap.
+ *
+ * This function is similar to wait(2) in that it returns information about a
+ * terminated task and allows to release the resources associated with the
+ * task. Until this function is called, the terminated task remains in a zombie
+ * state.
*
- * \param t The task to add.
- * \param s The scheduler instance to add the task to.
+ * \return If \a tptr is \p NULL, or \a *tptr is \p NULL, the function does
+ * nothing and returns zero. Otherwise, it is checked whether the task
+ * identified by \a tptr is still running. If it is, the function returns zero
+ * and again, no action is taken. Otherwise the (negative) error code of the
+ * terminated task is returned and \a *tptr is set to \p NULL. The task will
+ * then be removed removed from the scheduler task list.
*
- * \sa task::pre_select, task::post_select
+ * \sa \ref sched_shutdown(), wait(2).
*/
-void register_task(struct sched *s, struct task *t)
+int task_reap(struct task **tptr)
{
- PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
- assert(t->post_select);
- t->notification = 0;
+ struct task *t;
+ int ret;
+
+ if (!tptr)
+ return 0;
+ t = *tptr;
+ if (!t)
+ return 0;
+ if (t->status >= 0)
+ return 0;
+ ret = t->status;
+ /*
+ * With list_for_each_entry_safe() it is only safe to remove the
+ * _current_ list item. Since we are being called from the loop in
+ * schedule() via some task's ->post_select() function, freeing the
+ * given task here would result in use-after-free bugs in schedule().
+ * So we only set the task status to TS_DEAD which tells schedule() to
+ * free the task in the next iteration of its loop.
+ */
+ t->status = TS_DEAD;
+
+ *tptr = NULL;
+ return ret;
+}
+
+/**
+ * Deallocate all resources of all tasks of a scheduler instance.
+ *
+ * \param s The scheduler instance.
+ *
+ * This should only be called after \ref schedule() has returned.
+ */
+void sched_shutdown(struct sched *s)
+{
+ struct task *t, *tmp;
+
+ list_for_each_entry_safe(t, tmp, &s->task_list, node) {
+ if (t->status == TS_RUNNING)
+ /* The task list should contain only terminated tasks. */
+ PARA_WARNING_LOG("shutting down running task %s\n",
+ t->name);
+ unlink_and_free_task(t);
+ }
+}
+
+/**
+ * Add a task to the scheduler task list.
+ *
+ * \param info Task information supplied by the caller.
+ * \param s The scheduler instance.
+ *
+ * \return A pointer to a newly allocated task structure. It will be
+ * freed by sched_shutdown().
+ */
+struct task *task_register(struct task_info *info, struct sched *s)
+{
+ struct task *t = para_malloc(sizeof(*t));
+
+ assert(info->post_select);
+
if (!s->task_list.next)
INIT_LIST_HEAD(&s->task_list);
+
+ t->info = *info;
+ t->name = para_strdup(info->name);
+ t->notification = 0;
+ t->status = TS_RUNNING;
list_add_tail(&t->node, &s->task_list);
+ return t;
}
/**
list_for_each_entry_safe(t, tmp, &s->task_list, node) {
char *tmp_msg;
- tmp_msg = make_message("%s%p\t%s\n", msg? msg : "", t, t->status);
+ tmp_msg = make_message("%s%p\t%s\t%s\n", msg? msg : "", t,
+ t->status == TS_DEAD? "dead" :
+ (t->status == TS_RUNNING? "running" : "zombie"),
+ t->name);
free(msg);
msg = tmp_msg;
}
assert(err > 0);
if (t->notification == -err) /* ignore subsequent notifications */
return;
- PARA_INFO_LOG("notifying task %s: %s\n", t->status, para_strerror(err));
+ PARA_INFO_LOG("notifying task %s: %s\n", t->name, para_strerror(err));
t->notification = -err;
}
return t->notification;
}
+/**
+ * Return the status value of a task.
+ *
+ * \param t The task to get the status value from.
+ *
+ * \return Zero if task does not exist, one if task is running, negative error
+ * code if task has terminated.
+ */
+int task_status(const struct task *t)
+{
+ if (!t)
+ return 0;
+ if (t->status == TS_DEAD) /* pretend dead tasks don't exist */
+ return 0;
+ if (t->status == TS_RUNNING)
+ return 1;
+ return t->status;
+}
+
/**
* Set the notification value of all tasks of a scheduler instance.
*
projects / paraslash.git / blobdiff