--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-signal-multiple-loops.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,325 @@
+/* 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 test does not pretend to be cross-platform. */
+#ifndef _WIN32
+
+#include "uv.h"
+#include "task.h"
+
+#include <errno.h>
+#include <signal.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+/* The value of NUM_SIGNAL_HANDLING_THREADS is not arbitrary; it needs to be a
+ * multiple of three for reasons that will become clear when you scroll down.
+ * We're basically creating three different thread groups.  The total needs
+ * to be divisible by three in order for the numbers in the final check to
+ * match up.
+ */
+#define NUM_SIGNAL_HANDLING_THREADS 24
+#define NUM_LOOP_CREATING_THREADS 10
+
+enum signal_action {
+  ONLY_SIGUSR1,
+  ONLY_SIGUSR2,
+  SIGUSR1_AND_SIGUSR2
+};
+
+static uv_sem_t sem;
+static uv_mutex_t lock;
+static int stop = 0;
+
+static int signal1_cb_counter = 0;
+static int signal2_cb_counter = 0;
+static int loop_creation_counter = 0;
+
+
+static void increment_counter(int* counter) {
+  uv_mutex_lock(&lock);
+  ++(*counter);
+  uv_mutex_unlock(&lock);
+}
+
+
+static void signal1_cb(uv_signal_t* handle, int signum) {
+  ASSERT_EQ(signum, SIGUSR1);
+  increment_counter(&signal1_cb_counter);
+  uv_signal_stop(handle);
+}
+
+
+static void signal2_cb(uv_signal_t* handle, int signum) {
+  ASSERT_EQ(signum, SIGUSR2);
+  increment_counter(&signal2_cb_counter);
+  uv_signal_stop(handle);
+}
+
+
+static void signal_handling_worker(void* context) {
+  enum signal_action action;
+  uv_signal_t signal1a;
+  uv_signal_t signal1b;
+  uv_signal_t signal2;
+  uv_loop_t loop;
+  int r;
+
+  action = (enum signal_action) (uintptr_t) context;
+
+  ASSERT_OK(uv_loop_init(&loop));
+
+  /* Setup the signal watchers and start them. */
+  if (action == ONLY_SIGUSR1 || action == SIGUSR1_AND_SIGUSR2) {
+    r = uv_signal_init(&loop, &signal1a);
+    ASSERT_OK(r);
+    r = uv_signal_start(&signal1a, signal1_cb, SIGUSR1);
+    ASSERT_OK(r);
+    r = uv_signal_init(&loop, &signal1b);
+    ASSERT_OK(r);
+    r = uv_signal_start(&signal1b, signal1_cb, SIGUSR1);
+    ASSERT_OK(r);
+  }
+
+  if (action == ONLY_SIGUSR2 || action == SIGUSR1_AND_SIGUSR2) {
+    r = uv_signal_init(&loop, &signal2);
+    ASSERT_OK(r);
+    r = uv_signal_start(&signal2, signal2_cb, SIGUSR2);
+    ASSERT_OK(r);
+  }
+
+  /* Signal watchers are now set up. */
+  uv_sem_post(&sem);
+
+  /* Wait for all signals. The signal callbacks stop the watcher, so uv_run
+   * will return when all signal watchers caught a signal.
+   */
+  r = uv_run(&loop, UV_RUN_DEFAULT);
+  ASSERT_OK(r);
+
+  /* Restart the signal watchers. */
+  if (action == ONLY_SIGUSR1 || action == SIGUSR1_AND_SIGUSR2) {
+    r = uv_signal_start(&signal1a, signal1_cb, SIGUSR1);
+    ASSERT_OK(r);
+    r = uv_signal_start(&signal1b, signal1_cb, SIGUSR1);
+    ASSERT_OK(r);
+  }
+
+  if (action == ONLY_SIGUSR2 || action == SIGUSR1_AND_SIGUSR2) {
+    r = uv_signal_start(&signal2, signal2_cb, SIGUSR2);
+    ASSERT_OK(r);
+  }
+
+  /* Wait for signals once more. */
+  uv_sem_post(&sem);
+
+  r = uv_run(&loop, UV_RUN_DEFAULT);
+  ASSERT_OK(r);
+
+  /* Close the watchers. */
+  if (action == ONLY_SIGUSR1 || action == SIGUSR1_AND_SIGUSR2) {
+    uv_close((uv_handle_t*) &signal1a, NULL);
+    uv_close((uv_handle_t*) &signal1b, NULL);
+  }
+
+  if (action == ONLY_SIGUSR2 || action == SIGUSR1_AND_SIGUSR2) {
+    uv_close((uv_handle_t*) &signal2, NULL);
+  }
+
+  /* Wait for the signal watchers to close. */
+  r = uv_run(&loop, UV_RUN_DEFAULT);
+  ASSERT_OK(r);
+
+  uv_loop_close(&loop);
+}
+
+
+static void signal_unexpected_cb(uv_signal_t* handle, int signum) {
+  ASSERT(0 && "signal_unexpected_cb should never be called");
+}
+
+
+static void loop_creating_worker(void* context) {
+  int done;
+
+  (void) context;
+
+  do {
+    uv_loop_t *loop;
+    uv_signal_t signal;
+    int r;
+
+    loop = malloc(sizeof(*loop));
+    ASSERT_NOT_NULL(loop);
+    ASSERT_OK(uv_loop_init(loop));
+
+    r = uv_signal_init(loop, &signal);
+    ASSERT_OK(r);
+
+    r = uv_signal_start(&signal, signal_unexpected_cb, SIGTERM);
+    ASSERT_OK(r);
+
+    uv_close((uv_handle_t*) &signal, NULL);
+
+    r = uv_run(loop, UV_RUN_DEFAULT);
+    ASSERT_OK(r);
+
+    uv_loop_close(loop);
+    free(loop);
+
+    increment_counter(&loop_creation_counter);
+
+    uv_mutex_lock(&lock);
+    done = stop;
+    uv_mutex_unlock(&lock);
+  } while (!done);
+}
+
+
+TEST_IMPL(signal_multiple_loops) {
+#if defined(__CYGWIN__) || defined(__MSYS__)
+  /* FIXME: This test needs more investigation.  Somehow the `read` in
+     uv__signal_lock fails spuriously with EACCES or even EAGAIN even
+     though it is supposed to be blocking.  Also the test hangs during
+     thread setup occasionally.  */
+  RETURN_SKIP("FIXME: This test needs more investigation on Cygwin");
+#endif
+/* TODO(gengjiawen): Fix test on QEMU. */
+#if defined(__QEMU__)
+  /* See https://github.com/libuv/libuv/issues/2859 */
+  RETURN_SKIP("QEMU's signal emulation code is notoriously tricky");
+#endif
+#if defined(__ASAN__) || defined(__MSAN__)
+  /* See https://github.com/libuv/libuv/issues/3956 */
+  RETURN_SKIP("Test is too slow to run under ASan or MSan");
+#endif
+#if defined(__TSAN__)
+  /* ThreadSanitizer complains - likely legitimately - about data races
+   * in uv__signal_compare() in src/unix/signal.c but that's pre-existing.
+   */
+  RETURN_SKIP("Fix test under ThreadSanitizer");
+#endif
+  uv_thread_t loop_creating_threads[NUM_LOOP_CREATING_THREADS];
+  uv_thread_t signal_handling_threads[NUM_SIGNAL_HANDLING_THREADS];
+  enum signal_action action;
+  sigset_t sigset;
+  int i;
+  int r;
+
+  r = uv_sem_init(&sem, 0);
+  ASSERT_OK(r);
+
+  r = uv_mutex_init(&lock);
+  ASSERT_OK(r);
+
+  /* Create a couple of threads that create a destroy loops continuously. */
+  for (i = 0; i < NUM_LOOP_CREATING_THREADS; i++) {
+    r = uv_thread_create(&loop_creating_threads[i],
+                         loop_creating_worker,
+                         NULL);
+    ASSERT_OK(r);
+  }
+
+  /* Create a couple of threads that actually handle signals. */
+  for (i = 0; i < NUM_SIGNAL_HANDLING_THREADS; i++) {
+    switch (i % 3) {
+      case 0: action = ONLY_SIGUSR1; break;
+      case 1: action = ONLY_SIGUSR2; break;
+      case 2: action = SIGUSR1_AND_SIGUSR2; break;
+    }
+
+    r = uv_thread_create(&signal_handling_threads[i],
+                         signal_handling_worker,
+                         (void*) (uintptr_t) action);
+    ASSERT_OK(r);
+  }
+
+  /* Wait until all threads have started and set up their signal watchers. */
+  for (i = 0; i < NUM_SIGNAL_HANDLING_THREADS; i++)
+    uv_sem_wait(&sem);
+
+  r = kill(getpid(), SIGUSR1);
+  ASSERT_OK(r);
+  r = kill(getpid(), SIGUSR2);
+  ASSERT_OK(r);
+
+  /* Wait for all threads to handle these signals. */
+  for (i = 0; i < NUM_SIGNAL_HANDLING_THREADS; i++)
+    uv_sem_wait(&sem);
+
+  /* Block all signals to this thread, so we are sure that from here the signal
+   * handler runs in another thread. This is more likely to catch thread and
+   * signal safety issues if there are any.
+   */
+  sigfillset(&sigset);
+  pthread_sigmask(SIG_SETMASK, &sigset, NULL);
+
+  r = kill(getpid(), SIGUSR1);
+  ASSERT_OK(r);
+  r = kill(getpid(), SIGUSR2);
+  ASSERT_OK(r);
+
+  /* Wait for all signal handling threads to exit. */
+  for (i = 0; i < NUM_SIGNAL_HANDLING_THREADS; i++) {
+    r = uv_thread_join(&signal_handling_threads[i]);
+    ASSERT_OK(r);
+  }
+
+  /* Tell all loop creating threads to stop. */
+  uv_mutex_lock(&lock);
+  stop = 1;
+  uv_mutex_unlock(&lock);
+
+  /* Wait for all loop creating threads to exit. */
+  for (i = 0; i < NUM_LOOP_CREATING_THREADS; i++) {
+    r = uv_thread_join(&loop_creating_threads[i]);
+    ASSERT_OK(r);
+  }
+
+  uv_sem_destroy(&sem);
+  printf("signal1_cb calls: %d\n", signal1_cb_counter);
+  printf("signal2_cb calls: %d\n", signal2_cb_counter);
+  printf("loops created and destroyed: %d\n", loop_creation_counter);
+
+  /* The division by three reflects the fact that we spawn three different
+   * thread groups of (NUM_SIGNAL_HANDLING_THREADS / 3) threads each.
+   */
+  ASSERT_EQ(signal1_cb_counter, 8 * (NUM_SIGNAL_HANDLING_THREADS / 3));
+  ASSERT_EQ(signal2_cb_counter, 4 * (NUM_SIGNAL_HANDLING_THREADS / 3));
+
+  /* We don't know exactly how much loops will be created and destroyed, but at
+   * least there should be 1 for every loop creating thread.
+   */
+  ASSERT_GE(loop_creation_counter, NUM_LOOP_CREATING_THREADS);
+
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+}
+
+#else
+
+typedef int file_has_no_tests; /* ISO C forbids an empty translation unit. */
+
+#endif /* !_WIN32 */