Add scheduler documentation

and a GPL header

diff --git a/sched.h b/sched.h
index bd1ad796dfb4fa015e0053c05d83eeb5f5150704..8a6ed1a80fb9fca7493f311bbf9116234c19bdb3 100644 (file)
--- a/sched.h
+++ b/sched.h
@@ -1,22 +1,92 @@
+/*
+ * Copyright (C) 2006 Andre Noll <maan@systemlinux.org>
+ *
+ *     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.
+ *
+ *     This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ *
+ *     You should have received a copy of the GNU General Public License
+ *     along with this program; if not, write to the Free Software
+ *     Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
+ */
+
+/** \file sched.c Paraslash's task and scheduling functions */
+
+
+/**
+ * paraslash's scheduler
+ *
+ * desinged with KISS in mind. It maintains two lists: The pre_select list
+ * and the post_select list. Tasks add hokks to these lists by registering
+ * themselves to the scheduler.
+ */
 struct sched {
-       struct timeval now, timeout;
+       /** initial value before any pre_select call */
+       struct timeval default_timeout;
+       /** the current timeout for the upcoming select call */
+       struct timeval timeout;
+       /** fds that should be watched for readability */
+       fd_set rfds;
+       /** fds that should be watched for writability */
+       fd_set wfds;
+       /** highest numbered file descriptor in any of the above fd sets */
        int max_fileno;
-       fd_set rfds, wfds;
+       /** the return value of the previous select call */
        int select_ret;
-       struct timeval default_timeout;
 };
 
+/**
+ * paraslash's task structure
+ *
+ * before registering a task to the scheduler, the task structure must be
+ * filled in properly by the caller.
+ *
+ * The  pre_select or the post_select pointer, but not both may be NULL.  Once
+ * a task is registered, its pre_select and post_select function gets called
+ * from the scheduler's mainloop. The purpose of the pre_select loop is to add
+ * file descriptors to the fd sets of the scheduler and to decrease the select
+ * timeout if neccessary. The post_select function may then evaluate these fd
+ * sets and act upon the results.
+
+ * If one of these functions return a negative value via \a t->ret the
+ * (optional) event_handler gets called (it may also be called in case another
+ * event happend). In many cases the only possible event is an error or an eof
+ * condition and the event handler simply unregisters the task from the
+ * scheduler.
+ *
+ * \sa struct sched
+ */
 struct task {
+       /** pointer to the struct this task is embedded in */
        void *private_data;
-       int ret;
+       /** pre_select hook */
        void (*pre_select)(struct sched *s, struct task *t);
+       /** post_select hook */
        void (*post_select)(struct sched *s, struct task *t);
+       /** gets called */
        void (*event_handler)(struct task *t);
+       /** pre_select() and post_select store their return value here */
+       int ret;
+       /** position of the task in the pre_select list of the scheduler */
        struct list_head pre_select_node;
+       /** position of the task in the post_select list of the scheduler */
        struct list_head post_select_node;
+       /** descriptive text and current status of the task */
        char status[MAXLINE];
 };
 
+/**
+ * This is set by the scheduler at the beginning of its main loop.  It may be
+ * used (read-only) from everywhere. As none of the functions called by the
+ * scheduler are allowed to block, this value should be accurate enough so that
+ * there is no need to call gettimeofday() directly.
+ */
 extern struct timeval *now;
 
 void *register_task(struct task *t);