[ovs-dev] [flow-stats 08/14] poll-loop: Track the poll timeout as an absolute, not a relative time.
Ethan Jackson
ethan at nicira.com
Mon Dec 19 21:21:42 UTC 2011
> -/* Max time to wait in next call to poll_block(), in milliseconds, or -1 to
> +/* Time at which to wake up next call to poll_block(), in milliseconds as
> + * returned by time_msec(), LLONG_MIN to wake up immediately, or LLONG_MAX to
Oh also, did you mean to have a 'the' before 'next call to poll_block()'?
Ethan
> * wait forever. */
> -static int timeout = -1;
> +static long long int timeout_when = LLONG_MAX;
>
> /* Location where waiter created. */
> static const char *timeout_where;
> @@ -82,16 +83,6 @@ poll_fd_wait(int fd, short int events, const char *where)
> return new_waiter(fd, events, where);
> }
>
> -/* The caller must ensure that 'msec' is not negative. */
> -static void
> -poll_timer_wait__(int msec, const char *where)
> -{
> - if (timeout < 0 || msec < timeout) {
> - timeout = msec;
> - timeout_where = where;
> - }
> -}
> -
> /* Causes the following call to poll_block() to block for no more than 'msec'
> * milliseconds. If 'msec' is nonpositive, the following call to poll_block()
> * will not block at all.
> @@ -105,14 +96,25 @@ poll_timer_wait__(int msec, const char *where)
> void
> poll_timer_wait(long long int msec, const char *where)
> {
> - poll_timer_wait__((msec < 0 ? 0
> - : msec > INT_MAX ? INT_MAX
> - : msec),
> - where);
> + long long int now = time_msec();
> + long long int when;
> +
> + if (msec <= 0) {
> + /* Wake up immediately. */
> + when = LLONG_MIN;
> + } else if ((unsigned long long int) now + msec <= LLONG_MAX) {
> + /* Normal case. */
> + when = now + msec;
> + } else {
> + /* now + msec would overflow. */
> + when = LLONG_MAX;
> + }
> +
> + poll_timer_wait_until(when, where);
> }
>
> /* Causes the following call to poll_block() to wake up when the current time,
> - * as returned by time_msec(), reaches 'msec' or later. If 'msec' is earlier
> + * as returned by time_msec(), reaches 'when' or later. If 'when' is earlier
> * than the current time, the following call to poll_block() will not block at
> * all.
> *
> @@ -123,13 +125,12 @@ poll_timer_wait(long long int msec, const char *where)
> * Ordinarily the 'where' argument is supplied automatically; see poll-loop.h
> * for more information. */
> void
> -poll_timer_wait_until(long long int msec, const char *where)
> +poll_timer_wait_until(long long int when, const char *where)
> {
> - long long int now = time_msec();
> - poll_timer_wait__((msec <= now ? 0
> - : msec < now + INT_MAX ? msec - now
> - : INT_MAX),
> - where);
> + if (when < timeout_when) {
> + timeout_when = when;
> + timeout_where = where;
> + }
> }
>
> /* Causes the following call to poll_block() to wake up immediately, without
> @@ -215,6 +216,7 @@ poll_block(void)
>
> struct poll_waiter *pw, *next;
> int n_waiters, n_pollfds;
> + int elapsed;
> int retval;
>
> /* Register fatal signal events before actually doing any real work for
> @@ -236,15 +238,15 @@ poll_block(void)
> n_pollfds++;
> }
>
> - if (!timeout) {
> + if (timeout_when == LLONG_MIN) {
> COVERAGE_INC(poll_zero_timeout);
> }
> - retval = time_poll(pollfds, n_pollfds, timeout);
> + retval = time_poll(pollfds, n_pollfds, timeout_when, &elapsed);
> if (retval < 0) {
> static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
> VLOG_ERR_RL(&rl, "poll: %s", strerror(-retval));
> } else if (!retval) {
> - log_wakeup(timeout_where, NULL, timeout);
> + log_wakeup(timeout_where, NULL, elapsed);
> }
>
> LIST_FOR_EACH_SAFE (pw, next, node, &waiters) {
> @@ -254,7 +256,7 @@ poll_block(void)
> poll_cancel(pw);
> }
>
> - timeout = -1;
> + timeout_when = LLONG_MAX;
> timeout_where = NULL;
>
> /* Handle any pending signals before doing anything else. */
> diff --git a/lib/timeval.c b/lib/timeval.c
> index 88a6679..bc7411f 100644
> --- a/lib/timeval.c
> +++ b/lib/timeval.c
> @@ -269,16 +269,21 @@ time_alarm(unsigned int secs)
>
> /* Like poll(), except:
> *
> + * - The timeout is specified as an absolute time, as defined by
> + * time_msec(), instead of a duration.
> + *
> * - On error, returns a negative error code (instead of setting errno).
> *
> * - If interrupted by a signal, retries automatically until the original
> - * 'timeout' expires. (Because of this property, this function will
> + * timeout is reached. (Because of this property, this function will
> * never return -EINTR.)
> *
> * - As a side effect, refreshes the current time (like time_refresh()).
> - */
> + *
> + * Stores the number of milliseconds elapsed during poll in '*elapsed'. */
> int
> -time_poll(struct pollfd *pollfds, int n_pollfds, int timeout)
> +time_poll(struct pollfd *pollfds, int n_pollfds, long long int timeout_when,
> + int *elapsed)
> {
> static long long int last_wakeup;
> long long int start;
> @@ -292,12 +297,15 @@ time_poll(struct pollfd *pollfds, int n_pollfds, int timeout)
> start = time_msec();
> blocked = false;
> for (;;) {
> + long long int now = time_msec();
> int time_left;
> - if (timeout > 0) {
> - long long int elapsed = time_msec() - start;
> - time_left = timeout >= elapsed ? timeout - elapsed : 0;
> +
> + if (now >= timeout_when) {
> + time_left = 0;
> + } else if ((unsigned long long int) timeout_when - now > INT_MAX) {
> + time_left = INT_MAX;
> } else {
> - time_left = timeout;
> + time_left = timeout_when - now;
> }
>
> retval = poll(pollfds, n_pollfds, time_left);
> @@ -319,6 +327,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds, int timeout)
> }
> last_wakeup = time_msec();
> refresh_rusage();
> + *elapsed = last_wakeup - start;
> return retval;
> }
>
> diff --git a/lib/timeval.h b/lib/timeval.h
> index 517524c..e57f7ac 100644
> --- a/lib/timeval.h
> +++ b/lib/timeval.h
> @@ -55,7 +55,8 @@ long long int time_wall_msec(void);
> void time_timespec(struct timespec *);
> void time_wall_timespec(struct timespec *);
> void time_alarm(unsigned int secs);
> -int time_poll(struct pollfd *, int n_pollfds, int timeout);
> +int time_poll(struct pollfd *, int n_pollfds, long long int timeout_when,
> + int *elapsed);
>
> long long int timespec_to_msec(const struct timespec *);
> long long int timeval_to_msec(const struct timeval *);
> --
> 1.7.4.4
>
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