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Reduce latency of poll() on Windows

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When polling sockets poll() can now let you know about an event in about
10µs rather than 10ms. If you're not polling sockets then poll() reports
console events now in microseconds instead of milliseconds.
This commit is contained in:
Justine Tunney 2024-09-10 04:12:21 -07:00
parent a0a404a431
commit cceddd21b2
No known key found for this signature in database
GPG key ID: BE714B4575D6E328
5 changed files with 489 additions and 18 deletions
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53
libc/calls/poll-nt.c
View file

@ -28,6 +28,7 @@
#include "libc/errno.h"
#include "libc/intrin/atomic.h"
#include "libc/intrin/strace.h"
#include "libc/intrin/weaken.h"
#include "libc/macros.h"
#include "libc/mem/mem.h"
#include "libc/nt/console.h"
@ -48,6 +49,7 @@
#include "libc/stdio/sysparam.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/consts/poll.h"
#include "libc/sysv/consts/sicode.h"
#include "libc/sysv/consts/sig.h"
#include "libc/sysv/errfuns.h"
#include "libc/thread/posixthread.internal.h"
@ -78,13 +80,13 @@ static textwindows int sys_poll_nt_impl(struct pollfd *fds, uint64_t nfds,
uint32_t *ms, sigset_t sigmask) {
bool ok;
uint64_t millis;
uint32_t cm, avail, waitfor;
struct sys_pollfd_nt pipefds[64];
struct sys_pollfd_nt sockfds[64];
int pipeindices[ARRAYLEN(pipefds)];
int sockindices[ARRAYLEN(sockfds)];
struct timespec deadline, remain, now;
int i, rc, sn, pn, gotinvals, gotpipes, gotsocks;
uint32_t cm, avail, waitfor, already_slept;
int i, rc, sn, pn, sig, gotinvals, gotpipes, gotsocks, handler_was_called;
waitfor = ms ? *ms : -1u;
deadline = timespec_add(timespec_mono(), timespec_frommillis(waitfor));
@ -146,7 +148,20 @@ static textwindows int sys_poll_nt_impl(struct pollfd *fds, uint64_t nfds,
// perform the i/o and sleeping and looping
for (;;) {
// determine how long to wait
now = timespec_mono();
if (timespec_cmp(now, deadline) < 0) {
remain = timespec_sub(deadline, now);
millis = timespec_tomillis(remain);
waitfor = MIN(millis, 0xffffffffu);
waitfor = MIN(waitfor, POLL_INTERVAL_MS);
} else {
waitfor = 0;
}
// see if input is available on non-sockets
already_slept = 0;
for (gotpipes = i = 0; i < pn; ++i) {
if (pipefds[i].events & POLLWRNORM_)
// we have no way of polling if a non-socket is writeable yet
@ -171,7 +186,7 @@ static textwindows int sys_poll_nt_impl(struct pollfd *fds, uint64_t nfds,
// some programs like bash like to poll([stdin], 1, -1) so let's
// avoid busy looping in such cases. we could generalize this to
// always avoid busy loops, but we'd need poll to launch threads
if (0 && pn == 1 && sn == 0 && (pipefds[i].events & POLLRDNORM_)) {
if (!sn && (pipefds[i].events & POLLRDNORM_) && !already_slept++) {
int err = errno;
switch (CountConsoleInputBytesBlocking(waitfor, sigmask)) {
case -1:
@ -212,10 +227,12 @@ static textwindows int sys_poll_nt_impl(struct pollfd *fds, uint64_t nfds,
if (pipefds[i].revents)
++gotpipes;
}
// if we haven't found any good results yet then here we
// compute a small time slice we don't mind sleeping for
if (sn) {
if ((gotsocks = WSAPoll(sockfds, sn, 0)) == -1)
already_slept = 1;
if ((gotsocks = WSAPoll(sockfds, sn, waitfor)) == -1)
return __winsockerr();
} else {
gotsocks = 0;
@ -223,19 +240,21 @@ static textwindows int sys_poll_nt_impl(struct pollfd *fds, uint64_t nfds,
// add some artificial delay, which we use as an opportunity to also
// check for pending signals, thread cancelation, etc.
waitfor = 0;
if (!gotinvals && !gotsocks && !gotpipes) {
now = timespec_mono();
if (timespec_cmp(now, deadline) < 0) {
remain = timespec_sub(deadline, now);
millis = timespec_tomillis(remain);
waitfor = MIN(millis, 0xffffffffu);
waitfor = MIN(waitfor, POLL_INTERVAL_MS);
if (waitfor) {
POLLTRACE("poll() sleeping for %'d out of %'lu ms", waitfor,
timespec_tomillis(remain));
if (_park_norestart(waitfor, sigmask) == -1)
return -1; // eintr, ecanceled, etc.
if (!gotinvals && !gotsocks && !gotpipes && waitfor) {
if (!already_slept) {
POLLTRACE("poll() parking for %'d out of %'lu ms", waitfor,
timespec_tomillis(remain));
if (_park_norestart(waitfor, sigmask) == -1)
return -1; // eintr, ecanceled, etc.
} else {
if (_check_cancel() == -1)
return -1;
if (_weaken(__sig_get) && (sig = _weaken(__sig_get)(sigmask))) {
handler_was_called = _weaken(__sig_relay)(sig, SI_KERNEL, sigmask);
if (_check_cancel() == -1)
return -1;
if (handler_was_called)
return eintr();
}
}
}