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input: avoid using wakeup pipe if it's not needed 

If input is not waiting for select(), writing to the wakeup pipe is
wasteful, and, if there are many wakeups, might even block the wakeup
threads if the pipe gets full.

However, if it's waiting for select(), the wakup pipe must be used to
unblock the waiting thread. Actually there's a small race condition: we
might determine that the main thread is in select(), and write to the
wakeup pipe (whether we do this while unlocked or locked doesn't really
matter). Then, the main thread might leave select() before reading from
the wakup pipe. This should be harmless, because at worst more wakeups
than needed happen, but never fewer.
This commit is contained in:
wm4 2013-12-15 21:33:31 +01:00
parent 048bb2464d
commit e8f21b1f0a
1 changed files with 9 additions and 1 deletions
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10
mpvcore/input/input.c
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@ -607,6 +607,7 @@ struct input_ctx {
struct cmd_queue cmd_queue;
bool in_select;
int wakeup_pipe[2];
};
@ -1798,6 +1799,7 @@ static void input_wait_read(struct input_ctx *ictx, int time)
tv.tv_sec = time / 1000;
tv.tv_usec = (time % 1000) * 1000;
time_val = &tv;
ictx->in_select = true;
input_unlock(ictx);
if (select(max_fd + 1, &fds, NULL, NULL, time_val) < 0) {
if (errno != EINTR)
@ -1805,6 +1807,7 @@ static void input_wait_read(struct input_ctx *ictx, int time)
FD_ZERO(&fds);
}
input_lock(ictx);
ictx->in_select = false;
for (int i = 0; i < ictx->num_fds; i++) {
if (ictx->fds[i].select && !FD_ISSET(ictx->fds[i].fd, &fds))
continue;
@ -1874,6 +1877,7 @@ int mp_input_queue_cmd(struct input_ctx *ictx, mp_cmd_t *cmd)
if (cmd)
queue_add_tail(&ictx->cmd_queue, cmd);
input_unlock(ictx);
mp_input_wakeup(ictx);
return 1;
}
@ -2511,8 +2515,12 @@ static int print_cmd_list(m_option_t *cfg, char *optname, char *optparam)
void mp_input_wakeup(struct input_ctx *ictx)
{
input_lock(ictx);
bool send_wakeup = ictx->in_select;
ictx->got_new_events = true;
input_unlock(ictx);
// Safe without locking
if (ictx->wakeup_pipe[1] >= 0)
if (send_wakeup && ictx->wakeup_pipe[1] >= 0)
write(ictx->wakeup_pipe[1], &(char){0}, 1);
}