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Activate fd events in a pseudorandom order on older backends.

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New backends like poll and kqueue and so on add fds to the queue in
the order that they are triggered.  But the select backend currently
activates low-numbered fds first, whereas the poll and win32 backends
currently favor whatever fds have been on for the longest.  This is no
good for fairness.

svn:r1318
This commit is contained in:
Nick Mathewson 2009-05-27 15:35:00 +00:00
parent 11a178f2bd
commit cdaca02c29
4 changed files with 40 additions and 17 deletions
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1
ChangeLog
View File

@ -33,6 +33,7 @@ Changes in 2.0.2-alpha:
o Fix a deadlock when suspending reads in a bufferevent due to a full buffer. (Spotted by Joachim Bauch.)
o Fix a memory error when freeing a thread-enabled event base with registered events. (Spotted by Joachim Bauch.)
o Try to contain degree of failure when running on a win32 version so heavily firewalled that we can't fake a socketpair.
o Activate fd events in a pseudorandom order with O(N) backends, so that we don't systematically favor low fds (select) or earlier-added fds (poll, win32).
Changes in 2.0.1-alpha:

37
WIN32-Code/win32.c
View File

@ -282,8 +282,9 @@ win32_dispatch(struct event_base *base, struct timeval *tv)
{
struct win32op *win32op = base->evbase;
int res = 0;
unsigned i;
unsigned j, i;
int fd_count;
SOCKET s;
fd_set_copy(win32op->readset_out, win32op->readset_in);
fd_set_copy(win32op->exset_out, win32op->readset_in);
@ -314,19 +315,33 @@ win32_dispatch(struct event_base *base, struct timeval *tv)
evsig_process(base);
}
for (i=0; i<win32op->readset_out->fd_count; ++i) {
SOCKET s = win32op->readset_out->fd_array[i];
evmap_io_active(base, s, EV_READ);
if (win32op->readset_out->fd_count) {
i = rand() % win32op->readset_out->fd_count;
for (j=0; j<win32op->readset_out->fd_count; ++j) {
if (++i >= win32op->readset_out->fd_count)
i = 0;
s = win32op->readset_out->fd_array[i];
evmap_io_active(base, s, EV_READ);
}
}
for (i=0; i<win32op->exset_out->fd_count; ++i) {
SOCKET s = win32op->exset_out->fd_array[i];
evmap_io_active(base, s, EV_READ);
if (win32op->exset_out->fd_count) {
i = rand() % win32op->exset_out->fd_count;
for (j=0; j<win32op->exset_out->fd_count; ++j) {
if (++i >= win32op-exset_out->fd_count)
i = 0;
s = win32op->exset_out->fd_array[i];
evmap_io_active(base, s, EV_READ);
}
}
for (i=0; i<win32op->writeset_out->fd_count; ++i) {
SOCKET s = win32op->writeset_out->fd_array[i];
evmap_io_active(base, s, EV_WRITE);
if (win32op->writeset_out->fd_count) {
i = rand() % win32op->writeset_out->fd_count;
for (j=0; j<win32op->writeset_out->fd_count; ++j) {
if (++i >= win32op-exset_out->fd_count)
i = 0;
SOCKET s = win32op->writeset_out->fd_array[i];
evmap_io_active(base, s, EV_WRITE);
}
}
return (0);
}

12
poll.c
View File

@ -117,7 +117,7 @@ poll_check_ok(struct pollop *pop)
static int
poll_dispatch(struct event_base *base, struct timeval *tv)
{
int res, i, msec = -1, nfds;
int res, i, j, msec = -1, nfds;
struct pollop *pop = base->evbase;
poll_check_ok(pop);
@ -142,11 +142,15 @@ poll_dispatch(struct event_base *base, struct timeval *tv)
event_debug(("%s: poll reports %d", __func__, res));
if (res == 0)
if (res == 0 || nfds == 0)
return (0);
for (i = 0; i < nfds; i++) {
int what = pop->event_set[i].revents;
i = random() % nfds;
for (j = 0; j < nfds; j++) {
int what;
if (++i == nfds)
i = 0;
what = pop->event_set[i].revents;
if (!what)
continue;

7
select.c
View File

@ -114,7 +114,7 @@ check_selectop(struct selectop *sop)
static int
select_dispatch(struct event_base *base, struct timeval *tv)
{
int res, i;
int res, i, j;
struct selectop *sop = base->evbase;
check_selectop(sop);
@ -144,7 +144,10 @@ select_dispatch(struct event_base *base, struct timeval *tv)
event_debug(("%s: select reports %d", __func__, res));
check_selectop(sop);
for (i = 0; i <= sop->event_fds; ++i) {
i = random() % (sop->event_fds+1);
for (j = 0; j <= sop->event_fds; ++j) {
if (++i >= sop->event_fds+1)
i = 0;
res = 0;
if (FD_ISSET(i, sop->event_readset_out))
res |= EV_READ;