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improve comments and add more explanation about subtleties 

svn path=/trunk/netsurf/; revision=11686
This commit is contained in:
Vincent Sanders 2011-02-15 11:55:09 +00:00
parent e4035987a7
commit 3407760e64
2 changed files with 38 additions and 12 deletions
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22
windows/schedule.c
View File

@ -50,7 +50,6 @@ struct nscallback
* The callback function will be called as soon as possible after t cs have
* passed.
*/
void schedule(int cs_ival, void (*callback)(void *p), void *p)
{
struct nscallback *nscb;
@ -61,7 +60,7 @@ void schedule(int cs_ival, void (*callback)(void *p), void *p)
nscb = calloc(1, sizeof(struct nscallback));
LOG(("adding callback %p for %p(%p) at %d cs", nscb, callback, p, cs_ival));
LOG(("adding callback %p for %p(%p) at %d cs", nscb, callback, p, cs_ival));
gettimeofday(&nscb->tv, NULL);
timeradd(&nscb->tv, &tv, &nscb->tv);
@ -123,12 +122,8 @@ void schedule_remove(void (*callback)(void *p), void *p)
}
}
/**
* Process scheduled callbacks up to current time.
*
* @return The number of milliseconds untill the next scheduled event
* or -1 for no event.
*/
/* exported interface documented in schedule.h */
int
schedule_run(void)
{
@ -169,11 +164,13 @@ schedule_run(void)
free(unlnk_nscb);
/* need to deal with callback modifying the list. */
/* dispatched events can modify the list,
* instead of locking we simply reset list
* enumeration to the start.
*/
if (schedule_list == NULL)
return -1; /* no more callbacks scheduled */
/* reset enumeration to the start of the list */
cur_nscb = schedule_list;
prev_nscb = NULL;
nexttime = cur_nscb->tv;
@ -190,16 +187,17 @@ schedule_run(void)
}
}
/* make rettime relative to now */
/* make returned time relative to now */
timersub(&nexttime, &tv, &rettime);
#if DEBUG_SCHEDULER
#if defined(DEBUG_SCHEDULER)
LOG(("returning time to next event as %ldms",(rettime.tv_sec * 1000) + (rettime.tv_usec / 1000)));
#endif
/* return next event time in milliseconds (24days max wait) */
return (rettime.tv_sec * 1000) + (rettime.tv_usec / 1000);
}
/* exported interface documented in schedule.h */
void list_schedule(void)
{
struct timeval tv;

28
windows/schedule.h
View File

@ -19,7 +19,35 @@
#ifndef FRAMEBUFFER_SCHEDULE_H
#define FRAMEBUFFER_SCHEDULE_H
/**
* Process scheduled callbacks up to current time.
*
* This walks the list of outstanding scheduled events and dispatches
* them if they have met their scheduled time. Due to legacy issues
* there are a couple of subtleties with how this operates:
*
* - Generally there are so few entries on the list the overhead of
* ordering the list exceeds the cost of simply enumerating them.
*
* - The scheduled time is the time *after* which we should call the
* operation back, this can result in the next scheduled time
* being zero. This is exceedingly rare as the core schedules in
* 10ms (cs) quanta and we almost always get called to schedule
* after the event time.
*
* - The callbacks can cause the schedule list to be re-arranged added
* to or even completely deleted. This means we must reset the
* list enumeration to the beginning every time an event is
* dispatched.
*
* @return The number of milliseconds untill the next scheduled event
* or -1 for no event.
*/
int schedule_run(void);
/**
* LOG all current scheduled events.
*/
void list_schedule(void);
#endif