--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-async.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,134 @@
+/* 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.
+ */
+
+#include "uv.h"
+#include "task.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+static uv_thread_t thread;
+static uv_mutex_t mutex;
+
+static uv_prepare_t prepare;
+static uv_async_t async;
+
+static volatile int async_cb_called;
+static int prepare_cb_called;
+static int close_cb_called;
+
+
+static void thread_cb(void *arg) {
+  int n;
+  int r;
+
+  for (;;) {
+    uv_mutex_lock(&mutex);
+    n = async_cb_called;
+    uv_mutex_unlock(&mutex);
+
+    if (n == 3) {
+      break;
+    }
+
+    r = uv_async_send(&async);
+    ASSERT_OK(r);
+
+    /* Work around a bug in Valgrind.
+     *
+     * Valgrind runs threads not in parallel but sequentially, i.e. one after
+     * the other. It also doesn't preempt them, instead it depends on threads
+     * yielding voluntarily by making a syscall.
+     *
+     * That never happens here: the pipe that is associated with the async
+     * handle is written to once but that's too early for Valgrind's scheduler
+     * to kick in. Afterwards, the thread busy-loops, starving the main thread.
+     * Therefore, we yield.
+     *
+     * This behavior has been observed with Valgrind 3.7.0 and 3.9.0.
+     */
+    uv_sleep(0);
+  }
+}
+
+
+static void close_cb(uv_handle_t* handle) {
+  ASSERT_NOT_NULL(handle);
+  close_cb_called++;
+}
+
+
+static void async_cb(uv_async_t* handle) {
+  int n;
+
+  ASSERT_PTR_EQ(handle, &async);
+
+  uv_mutex_lock(&mutex);
+  n = ++async_cb_called;
+  uv_mutex_unlock(&mutex);
+
+  if (n == 3) {
+    uv_close((uv_handle_t*)&async, close_cb);
+    uv_close((uv_handle_t*)&prepare, close_cb);
+  }
+}
+
+
+static void prepare_cb(uv_prepare_t* handle) {
+  int r;
+
+  ASSERT_PTR_EQ(handle, &prepare);
+
+  if (prepare_cb_called++)
+    return;
+
+  r = uv_thread_create(&thread, thread_cb, NULL);
+  ASSERT_OK(r);
+  uv_mutex_unlock(&mutex);
+}
+
+
+TEST_IMPL(async) {
+  int r;
+
+  r = uv_mutex_init(&mutex);
+  ASSERT_OK(r);
+  uv_mutex_lock(&mutex);
+
+  r = uv_prepare_init(uv_default_loop(), &prepare);
+  ASSERT_OK(r);
+  r = uv_prepare_start(&prepare, prepare_cb);
+  ASSERT_OK(r);
+
+  r = uv_async_init(uv_default_loop(), &async, async_cb);
+  ASSERT_OK(r);
+
+  r = uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+  ASSERT_OK(r);
+
+  ASSERT_GT(prepare_cb_called, 0);
+  ASSERT_EQ(3, async_cb_called);
+  ASSERT_EQ(2, close_cb_called);
+
+  ASSERT_OK(uv_thread_join(&thread));
+
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+}