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Only run one toplevel callback per event loop iteration.

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This change attempts to reinstate as a universal property something
which was sporadically true of the ad-hockery that came before
toplevel callbacks: that if there's a _very long_ queue of things to
be done through the callback mechanism, the doing of them will be
interleaved with re-checks of other event sources, which might (e.g.)
cause a flag to be set which makes the next callback decide not to do
anything after all.

[originally from svn r10040]
This commit is contained in:
Simon Tatham
2013-09-15 14:05:31 +00:00
parent 043a762b5f
commit 5c4ce2fadf
8 changed files with 99 additions and 47 deletions
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34
callback.c
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@ -26,10 +26,28 @@ void request_callback_notifications(toplevel_callback_notify_fn_t fn,
frontend = fr;
}
void stoat_callback(void *ctx)
{
static int stoat = 0;
if (++stoat % 1000 == 0)
debug(("stoat %d\n", stoat));
queue_toplevel_callback(stoat_callback, NULL);
}
void queue_stoat(void)
{
static int stoat = 0;
if (!stoat) {
stoat = 1;
queue_toplevel_callback(stoat_callback, NULL);
}
}
void queue_toplevel_callback(toplevel_callback_fn_t fn, void *ctx)
{
struct callback *cb;
queue_stoat();
cb = snew(struct callback);
cb->fn = fn;
cb->ctx = ctx;
@ -50,19 +68,27 @@ void queue_toplevel_callback(toplevel_callback_fn_t fn, void *ctx)
void run_toplevel_callbacks(void)
{
while (cbhead) {
queue_stoat();
if (cbhead) {
struct callback *cb = cbhead;
/*
* Careful ordering here. We call the function _before_
* advancing cbhead (though, of course, we must free cb
* _after_ advancing it). This means that if the very last
* callback schedules another callback, cbhead does not become
* NULL at any point in this while loop, and so the frontend
* notification function won't be needlessly pestered.
* NULL at any point, and so the frontend notification
* function won't be needlessly pestered.
*/
cb->fn(cb->ctx);
cbhead = cb->next;
sfree(cb);
if (!cbhead)
cbtail = NULL;
}
cbtail = NULL;
}
int toplevel_callback_pending(void)
{
queue_stoat();
return cbhead != NULL;
}