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velzieandClaude Opus 4.8
14bc64c3e6
eventfd and timerfd each have unit tests and were checked by hand against a guest, but the thing they exist for is the three composed -- an epoll loop that an eventfd wakes and a timerfd paces, which is the core of libuv and so of Node. This runs exactly that and requires byte-identical output against QEMU. Deterministic on purpose so QEMU can be the oracle: a one-shot timer and a fixed eventfd counter, output that names what happened rather than when. The eventfd is ready before the loop and the timer fires 30ms in, so the order is fixed -- eventfd, then timer -- and both engines print the same four lines. Co-Authored-By: Claude Opus 4.8 <[email protected]> Claude-Session: https://claude.ai/code/session_019b4VWMhJUWoGKQh4EeFfPm
68 lines
2.3 KiB
C
68 lines
2.3 KiB
C
/* epoll over an eventfd and a timerfd -- the core an event loop is built on.
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*
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* Deterministic on purpose, so QEMU can be the oracle: a one-shot timer and a
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* fixed eventfd counter, with output that names *what* happened rather than
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* *when*. The timing (how long epoll_wait blocks) differs between engines; the
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* bytes printed do not.
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*/
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#include <sys/epoll.h>
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#include <sys/eventfd.h>
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#include <sys/timerfd.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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int main(void) {
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int ep = epoll_create1(0);
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int ef = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
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int tf = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
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if (ep < 0 || ef < 0 || tf < 0) {
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perror("create");
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return 1;
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}
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/* A one-shot timer 30ms out, and an eventfd already carrying a count. */
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struct itimerspec its;
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memset(&its, 0, sizeof its);
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its.it_value.tv_nsec = 30 * 1000 * 1000;
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timerfd_settime(tf, 0, &its, NULL);
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uint64_t seed = 7;
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write(ef, &seed, 8);
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struct epoll_event add = {.events = EPOLLIN, .data.fd = ef};
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epoll_ctl(ep, EPOLL_CTL_ADD, ef, &add);
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add.data.fd = tf;
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epoll_ctl(ep, EPOLL_CTL_ADD, tf, &add);
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int saw_ef = 0, saw_tf = 0;
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struct epoll_event out[4];
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/* Loop until both fds have been seen ready and drained once. */
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while (!(saw_ef && saw_tf)) {
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int n = epoll_wait(ep, out, 4, 2000);
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if (n <= 0) {
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printf("timed out waiting (saw_ef=%d saw_tf=%d)\n", saw_ef, saw_tf);
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return 1;
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}
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for (int i = 0; i < n; i++) {
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uint64_t v = 0;
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if (out[i].data.fd == ef && !saw_ef) {
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if (read(ef, &v, 8) == 8) {
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printf("eventfd delivered %llu\n", (unsigned long long)v);
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saw_ef = 1;
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}
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} else if (out[i].data.fd == tf && !saw_tf) {
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if (read(tf, &v, 8) == 8) {
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printf("timerfd fired, expirations %llu\n", (unsigned long long)v);
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saw_tf = 1;
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}
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}
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}
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}
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/* Both drained: a further wait with no timer armed times out at once. */
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int n = epoll_wait(ep, out, 4, 0);
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printf("drained, epoll_wait ready=%d\n", n);
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printf("event loop ok\n");
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return 0;
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}
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