--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-mutexes.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,182 @@
+/* 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_cond_t condvar;
+static uv_mutex_t mutex;
+static uv_rwlock_t rwlock;
+static int step;
+
+/* The mutex and rwlock tests are really poor.
+ * They're very basic sanity checks and nothing more.
+ * Apologies if that rhymes.
+ */
+
+TEST_IMPL(thread_mutex) {
+  uv_mutex_t mutex;
+  int r;
+
+  r = uv_mutex_init(&mutex);
+  ASSERT_OK(r);
+
+  uv_mutex_lock(&mutex);
+  uv_mutex_unlock(&mutex);
+  uv_mutex_destroy(&mutex);
+
+  return 0;
+}
+
+
+TEST_IMPL(thread_mutex_recursive) {
+  uv_mutex_t mutex;
+  int r;
+
+  r = uv_mutex_init_recursive(&mutex);
+  ASSERT_OK(r);
+
+  uv_mutex_lock(&mutex);
+  uv_mutex_lock(&mutex);
+  ASSERT_OK(uv_mutex_trylock(&mutex));
+
+  uv_mutex_unlock(&mutex);
+  uv_mutex_unlock(&mutex);
+  uv_mutex_unlock(&mutex);
+  uv_mutex_destroy(&mutex);
+
+  return 0;
+}
+
+
+TEST_IMPL(thread_rwlock) {
+  uv_rwlock_t rwlock;
+  int r;
+
+  r = uv_rwlock_init(&rwlock);
+  ASSERT_OK(r);
+
+  uv_rwlock_rdlock(&rwlock);
+  uv_rwlock_rdunlock(&rwlock);
+  uv_rwlock_wrlock(&rwlock);
+  uv_rwlock_wrunlock(&rwlock);
+  uv_rwlock_destroy(&rwlock);
+
+  return 0;
+}
+
+
+/* Call when holding |mutex|. */
+static void synchronize_nowait(void) {
+  step += 1;
+  uv_cond_signal(&condvar);
+}
+
+
+/* Call when holding |mutex|. */
+static void synchronize(void) {
+  int current;
+
+  synchronize_nowait();
+  /* Wait for the other thread.  Guard against spurious wakeups. */
+  for (current = step; current == step; uv_cond_wait(&condvar, &mutex));
+  ASSERT_EQ(step, current + 1);
+}
+
+
+static void thread_rwlock_trylock_peer(void* unused) {
+  (void) &unused;
+
+  uv_mutex_lock(&mutex);
+
+  /* Write lock held by other thread. */
+  ASSERT_EQ(UV_EBUSY, uv_rwlock_tryrdlock(&rwlock));
+  ASSERT_EQ(UV_EBUSY, uv_rwlock_trywrlock(&rwlock));
+  synchronize();
+
+  /* Read lock held by other thread. */
+  ASSERT_OK(uv_rwlock_tryrdlock(&rwlock));
+  uv_rwlock_rdunlock(&rwlock);
+  ASSERT_EQ(UV_EBUSY, uv_rwlock_trywrlock(&rwlock));
+  synchronize();
+
+  /* Acquire write lock. */
+  ASSERT_OK(uv_rwlock_trywrlock(&rwlock));
+  synchronize();
+
+  /* Release write lock and acquire read lock. */
+  uv_rwlock_wrunlock(&rwlock);
+  ASSERT_OK(uv_rwlock_tryrdlock(&rwlock));
+  synchronize();
+
+  uv_rwlock_rdunlock(&rwlock);
+  synchronize_nowait();  /* Signal main thread we're going away. */
+  uv_mutex_unlock(&mutex);
+}
+
+
+TEST_IMPL(thread_rwlock_trylock) {
+  uv_thread_t thread;
+
+  ASSERT_OK(uv_cond_init(&condvar));
+  ASSERT_OK(uv_mutex_init(&mutex));
+  ASSERT_OK(uv_rwlock_init(&rwlock));
+
+  uv_mutex_lock(&mutex);
+  ASSERT_OK(uv_thread_create(&thread, thread_rwlock_trylock_peer, NULL));
+
+  /* Hold write lock. */
+  ASSERT_OK(uv_rwlock_trywrlock(&rwlock));
+  synchronize();  /* Releases the mutex to the other thread. */
+
+  /* Release write lock and acquire read lock.  Pthreads doesn't support
+   * the notion of upgrading or downgrading rwlocks, so neither do we.
+   */
+  uv_rwlock_wrunlock(&rwlock);
+  ASSERT_OK(uv_rwlock_tryrdlock(&rwlock));
+  synchronize();
+
+  /* Release read lock. */
+  uv_rwlock_rdunlock(&rwlock);
+  synchronize();
+
+  /* Write lock held by other thread. */
+  ASSERT_EQ(UV_EBUSY, uv_rwlock_tryrdlock(&rwlock));
+  ASSERT_EQ(UV_EBUSY, uv_rwlock_trywrlock(&rwlock));
+  synchronize();
+
+  /* Read lock held by other thread. */
+  ASSERT_OK(uv_rwlock_tryrdlock(&rwlock));
+  uv_rwlock_rdunlock(&rwlock);
+  ASSERT_EQ(UV_EBUSY, uv_rwlock_trywrlock(&rwlock));
+  synchronize();
+
+  ASSERT_OK(uv_thread_join(&thread));
+  uv_rwlock_destroy(&rwlock);
+  uv_mutex_unlock(&mutex);
+  uv_mutex_destroy(&mutex);
+  uv_cond_destroy(&condvar);
+
+  return 0;
+}