--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/src/unix/async.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,418 @@
+/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+/* This file contains both the uv__async internal infrastructure and the
+ * user-facing uv_async_t functions.
+ */
+
+#include "uv.h"
+#include "internal.h"
+
+#include <errno.h>
+#include <stdatomic.h>
+#include <stdio.h>  /* snprintf() */
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sched.h>  /* sched_yield() */
+
+#ifdef __linux__
+#include <sys/eventfd.h>
+#endif
+
+#if UV__KQUEUE_EVFILT_USER
+static uv_once_t kqueue_runtime_detection_guard = UV_ONCE_INIT;
+static int kqueue_evfilt_user_support = 1;
+
+
+static void uv__kqueue_runtime_detection(void) {
+  int kq;
+  struct kevent ev[2];
+  struct timespec timeout = {0, 0};
+
+  /* Perform the runtime detection to ensure that kqueue with
+   * EVFILT_USER actually works. */
+  kq = kqueue();
+  EV_SET(ev, UV__KQUEUE_EVFILT_USER_IDENT, EVFILT_USER,
+         EV_ADD | EV_CLEAR, 0, 0, 0);
+  EV_SET(ev + 1, UV__KQUEUE_EVFILT_USER_IDENT, EVFILT_USER,
+         0, NOTE_TRIGGER, 0, 0);
+  if (kevent(kq, ev, 2, ev, 1, &timeout) < 1 ||
+      ev[0].filter != EVFILT_USER ||
+      ev[0].ident != UV__KQUEUE_EVFILT_USER_IDENT ||
+      ev[0].flags & EV_ERROR)
+    /* If we wind up here, we can assume that EVFILT_USER is defined but
+     * broken on the current system. */
+    kqueue_evfilt_user_support = 0;
+  uv__close(kq);
+}
+#endif
+
+static void uv__async_send(uv_loop_t* loop);
+static int uv__async_start(uv_loop_t* loop);
+static void uv__cpu_relax(void);
+
+
+int uv_async_init(uv_loop_t* loop, uv_async_t* handle, uv_async_cb async_cb) {
+  int err;
+
+  err = uv__async_start(loop);
+  if (err)
+    return err;
+
+  uv__handle_init(loop, (uv_handle_t*)handle, UV_ASYNC);
+  handle->async_cb = async_cb;
+  handle->pending = 0;
+  handle->u.fd = 0; /* This will be used as a busy flag. */
+
+  uv__queue_insert_tail(&loop->async_handles, &handle->queue);
+  uv__handle_start(handle);
+
+  return 0;
+}
+
+
+int uv_async_send(uv_async_t* handle) {
+  _Atomic int* pending;
+  _Atomic int* busy;
+
+  pending = (_Atomic int*) &handle->pending;
+  busy = (_Atomic int*) &handle->u.fd;
+
+  /* Do a cheap read first. */
+  if (atomic_load_explicit(pending, memory_order_relaxed) != 0)
+    return 0;
+
+  /* Set the loop to busy. */
+  atomic_fetch_add(busy, 1);
+
+  /* Wake up the other thread's event loop. */
+  if (atomic_exchange(pending, 1) == 0)
+    uv__async_send(handle->loop);
+
+  /* Set the loop to not-busy. */
+  atomic_fetch_add(busy, -1);
+
+  return 0;
+}
+
+
+/* Wait for the busy flag to clear before closing.
+ * Only call this from the event loop thread. */
+static void uv__async_spin(uv_async_t* handle) {
+  _Atomic int* pending;
+  _Atomic int* busy;
+  int i;
+
+  pending = (_Atomic int*) &handle->pending;
+  busy = (_Atomic int*) &handle->u.fd;
+
+  /* Set the pending flag first, so no new events will be added by other
+   * threads after this function returns. */
+  atomic_store(pending, 1);
+
+  for (;;) {
+    /* 997 is not completely chosen at random. It's a prime number, acyclic by
+     * nature, and should therefore hopefully dampen sympathetic resonance.
+     */
+    for (i = 0; i < 997; i++) {
+      if (atomic_load(busy) == 0)
+        return;
+
+      /* Other thread is busy with this handle, spin until it's done. */
+      uv__cpu_relax();
+    }
+
+    /* Yield the CPU. We may have preempted the other thread while it's
+     * inside the critical section and if it's running on the same CPU
+     * as us, we'll just burn CPU cycles until the end of our time slice.
+     */
+    sched_yield();
+  }
+}
+
+
+void uv__async_close(uv_async_t* handle) {
+  uv__async_spin(handle);
+  uv__queue_remove(&handle->queue);
+  uv__handle_stop(handle);
+}
+
+
+static void uv__async_io(uv_loop_t* loop, uv__io_t* w, unsigned int events) {
+  char buf[1024];
+  ssize_t r;
+  struct uv__queue queue;
+  struct uv__queue* q;
+  uv_async_t* h;
+  _Atomic int *pending;
+
+  assert(w == &loop->async_io_watcher);
+
+#if UV__KQUEUE_EVFILT_USER
+  for (;!kqueue_evfilt_user_support;) {
+#else
+  for (;;) {
+#endif
+    r = read(w->fd, buf, sizeof(buf));
+
+    if (r == sizeof(buf))
+      continue;
+
+    if (r != -1)
+      break;
+
+    if (errno == EAGAIN || errno == EWOULDBLOCK)
+      break;
+
+    if (errno == EINTR)
+      continue;
+
+    abort();
+  }
+
+  uv__queue_move(&loop->async_handles, &queue);
+  while (!uv__queue_empty(&queue)) {
+    q = uv__queue_head(&queue);
+    h = uv__queue_data(q, uv_async_t, queue);
+
+    uv__queue_remove(q);
+    uv__queue_insert_tail(&loop->async_handles, q);
+
+    /* Atomically fetch and clear pending flag */
+    pending = (_Atomic int*) &h->pending;
+    if (atomic_exchange(pending, 0) == 0)
+      continue;
+
+    if (h->async_cb == NULL)
+      continue;
+
+    h->async_cb(h);
+  }
+}
+
+
+static void uv__async_send(uv_loop_t* loop) {
+  const void* buf;
+  ssize_t len;
+  int fd;
+  int r;
+
+  buf = "";
+  len = 1;
+  fd = loop->async_wfd;
+
+#if defined(__linux__)
+  if (fd == -1) {
+    static const uint64_t val = 1;
+    buf = &val;
+    len = sizeof(val);
+    fd = loop->async_io_watcher.fd;  /* eventfd */
+  }
+#elif UV__KQUEUE_EVFILT_USER
+  struct kevent ev;
+
+  if (kqueue_evfilt_user_support) {
+    fd = loop->async_io_watcher.fd; /* magic number for EVFILT_USER */
+    EV_SET(&ev, fd, EVFILT_USER, 0, NOTE_TRIGGER, 0, 0);
+    r = kevent(loop->backend_fd, &ev, 1, NULL, 0, NULL);
+    if (r == 0)
+      return;
+    abort();
+  }
+#endif
+
+  do
+    r = write(fd, buf, len);
+  while (r == -1 && errno == EINTR);
+
+  if (r == len)
+    return;
+
+  if (r == -1)
+    if (errno == EAGAIN || errno == EWOULDBLOCK)
+      return;
+
+  abort();
+}
+
+
+static int uv__async_start(uv_loop_t* loop) {
+  int pipefd[2];
+  int err;
+#if UV__KQUEUE_EVFILT_USER
+  struct kevent ev;
+#endif
+
+  if (loop->async_io_watcher.fd != -1)
+    return 0;
+
+#ifdef __linux__
+  err = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
+  if (err < 0)
+    return UV__ERR(errno);
+
+  pipefd[0] = err;
+  pipefd[1] = -1;
+#elif UV__KQUEUE_EVFILT_USER
+  uv_once(&kqueue_runtime_detection_guard, uv__kqueue_runtime_detection);
+  if (kqueue_evfilt_user_support) {
+    /* In order not to break the generic pattern of I/O polling, a valid
+     * file descriptor is required to take up a room in loop->watchers,
+     * thus we create one for that, but this fd will not be actually used,
+     * it's just a placeholder and magic number which is going to be closed
+     * during the cleanup, as other FDs. */
+    err = uv__open_cloexec("/", O_RDONLY);
+    if (err < 0)
+      return err;
+
+    pipefd[0] = err;
+    pipefd[1] = -1;
+
+    /* When using EVFILT_USER event to wake up the kqueue, this event must be
+     * registered beforehand. Otherwise, calling kevent() to issue an
+     * unregistered EVFILT_USER event will get an ENOENT.
+     * Since uv__async_send() may happen before uv__io_poll() with multi-threads,
+     * we can't defer this registration of EVFILT_USER event as we did for other
+     * events, but must perform it right away. */
+    EV_SET(&ev, err, EVFILT_USER, EV_ADD | EV_CLEAR, 0, 0, 0);
+    err = kevent(loop->backend_fd, &ev, 1, NULL, 0, NULL);
+    if (err < 0)
+      return UV__ERR(errno);
+  } else {
+    err = uv__make_pipe(pipefd, UV_NONBLOCK_PIPE);
+    if (err < 0)
+      return err;
+  }
+#else
+  err = uv__make_pipe(pipefd, UV_NONBLOCK_PIPE);
+  if (err < 0)
+    return err;
+#endif
+
+  err = uv__io_init_start(loop, &loop->async_io_watcher, uv__async_io,
+                          pipefd[0], POLLIN);
+  if (err < 0) {
+    uv__close(pipefd[0]);
+    if (pipefd[1] != -1)
+      uv__close(pipefd[1]);
+    return err;
+  }
+  loop->async_wfd = pipefd[1];
+
+#if UV__KQUEUE_EVFILT_USER
+  /* Prevent the EVFILT_USER event from being added to kqueue redundantly
+   * and mistakenly later in uv__io_poll(). */
+  if (kqueue_evfilt_user_support)
+    loop->async_io_watcher.events = loop->async_io_watcher.pevents;
+#endif
+
+  return 0;
+}
+
+
+void uv__async_stop(uv_loop_t* loop) {
+  struct uv__queue queue;
+  struct uv__queue* q;
+  uv_async_t* h;
+
+  if (loop->async_io_watcher.fd == -1)
+    return;
+
+  /* Make sure no other thread is accessing the async handle fd after the loop
+   * cleanup.
+   */
+  uv__queue_move(&loop->async_handles, &queue);
+  while (!uv__queue_empty(&queue)) {
+    q = uv__queue_head(&queue);
+    h = uv__queue_data(q, uv_async_t, queue);
+
+    uv__queue_remove(q);
+    uv__queue_insert_tail(&loop->async_handles, q);
+
+    uv__async_spin(h);
+  }
+
+  if (loop->async_wfd != -1) {
+    if (loop->async_wfd != loop->async_io_watcher.fd)
+      uv__close(loop->async_wfd);
+    loop->async_wfd = -1;
+  }
+
+  uv__io_stop(loop, &loop->async_io_watcher, POLLIN);
+  uv__close(loop->async_io_watcher.fd);
+  loop->async_io_watcher.fd = -1;
+}
+
+
+int uv__async_fork(uv_loop_t* loop) {
+  struct uv__queue queue;
+  struct uv__queue* q;
+  uv_async_t* h;
+
+  if (loop->async_io_watcher.fd == -1) /* never started */
+    return 0;
+
+  uv__queue_move(&loop->async_handles, &queue);
+  while (!uv__queue_empty(&queue)) {
+    q = uv__queue_head(&queue);
+    h = uv__queue_data(q, uv_async_t, queue);
+
+    uv__queue_remove(q);
+    uv__queue_insert_tail(&loop->async_handles, q);
+
+    /* The state of any thread that set pending is now likely corrupt in this
+     * child because the user called fork, so just clear these flags and move
+     * on. Calling most libc functions after `fork` is declared to be undefined
+     * behavior anyways, unless async-signal-safe, for multithreaded programs
+     * like libuv, and nothing interesting in pthreads is async-signal-safe.
+     */
+    h->pending = 0;
+    /* This is the busy flag, and we just abruptly lost all other threads. */
+    h->u.fd = 0;
+  }
+
+  /* Recreate these, since they still exist, but belong to the wrong pid now. */
+  if (loop->async_wfd != -1) {
+    if (loop->async_wfd != loop->async_io_watcher.fd)
+      uv__close(loop->async_wfd);
+    loop->async_wfd = -1;
+  }
+
+  uv__io_stop(loop, &loop->async_io_watcher, POLLIN);
+  uv__close(loop->async_io_watcher.fd);
+  loop->async_io_watcher.fd = -1;
+
+  return uv__async_start(loop);
+}
+
+
+static void uv__cpu_relax(void) {
+#if defined(__i386__) || defined(__x86_64__)
+  __asm__ __volatile__ ("rep; nop" ::: "memory");  /* a.k.a. PAUSE */
+#elif (defined(__arm__) && __ARM_ARCH >= 7) || defined(__aarch64__)
+  __asm__ __volatile__ ("yield" ::: "memory");
+#elif (defined(__ppc__) || defined(__ppc64__)) && defined(__APPLE__)
+  __asm volatile ("" : : : "memory");
+#elif !defined(__APPLE__) && (defined(__powerpc64__) || defined(__ppc64__) || defined(__PPC64__))
+  __asm__ __volatile__ ("or 1,1,1; or 2,2,2" ::: "memory");
+#endif
+}