Simplify the scheduling code.
[paraslash.git] / sched.h
1 /*
2 * Copyright (C) 2006 Andre Noll <maan@systemlinux.org>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6
7 /** \file sched.h sched and task structures and exported symbols from sched.c */
8
9
10 /**
11 * paraslash's scheduler
12 *
13 * Designed with KISS in mind. It manages two lists of tasks. The pre_select
14 * list contains pointers to functions that are called before calling select()
15 * from the main loop. Similarly, \a post_select_list is a list of function
16 * pointers each of which is called after the select call. Tasks add hooks to
17 * these lists by registering themselves to the scheduler.
18 */
19 struct sched {
20 /** initial value before any pre_select call */
21 struct timeval default_timeout;
22 /** the current timeout for the upcoming select call */
23 struct timeval timeout;
24 /** fds that should be watched for readability */
25 fd_set rfds;
26 /** fds that should be watched for writability */
27 fd_set wfds;
28 /** highest numbered file descriptor in any of the above fd sets */
29 int max_fileno;
30 };
31
32 /**
33 * paraslash's task structure
34 *
35 * before registering a task to the scheduler, the task structure must be
36 * filled in properly by the caller.
37 *
38 * If one of these functions return a negative value via \a t->ret the
39 * (optional) event_handler gets called (it may also be called in case another
40 * event happened). In many cases the only possible event is an error or an eof
41 * condition and the event handler simply unregisters the task from the
42 * scheduler.
43 *
44 * \sa struct sched
45 */
46 struct task {
47 /**
48 * the pre select hook of \a t
49 *
50 * Its purpose is to add file descriptors to the fd sets of the
51 * scheduler and to decrease the select timeout if necessary.
52 */
53 void (*pre_select)(struct sched *s, struct task *t);
54 /**
55 * the postselect hook of \a t
56 *
57 * evaluate and act upon the results of the previous select call.
58 */
59 void (*post_select)(struct sched *s, struct task *t);
60 /** Whether this task is in error state. */
61 int error;
62 /** position of the task in the pre_select list of the scheduler */
63 struct list_head pre_select_node;
64 /** position of the task in the post_select list of the scheduler */
65 struct list_head post_select_node;
66 /** descriptive text and current status of the task */
67 char status[MAXLINE];
68 };
69
70 /**
71 * This is set by the scheduler at the beginning of its main loop. It may be
72 * used (read-only) from everywhere. As none of the functions called by the
73 * scheduler are allowed to block, this value should be accurate enough so that
74 * there is no need to call gettimeofday() directly.
75 */
76 extern struct timeval *now;
77
78 void register_task(struct task *t);
79 void unregister_task(struct task *t);
80 int schedule(struct sched *s);
81 char *get_task_list(void);
82 int kill_task(char *id);