--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-thread-affinity.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,154 @@
+/* Copyright libuv project 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 <string.h>
+
+#ifndef NO_CPU_AFFINITY
+
+static void check_affinity(void* arg) {
+  int r;
+  char* cpumask;
+  int cpumasksize;
+  uv_thread_t tid;
+
+  cpumask = (char*)arg;
+  cpumasksize = uv_cpumask_size();
+  ASSERT_GT(cpumasksize, 0);
+  tid = uv_thread_self();
+  r = uv_thread_setaffinity(&tid, cpumask, NULL, cpumasksize);
+  ASSERT_OK(r);
+  r = uv_thread_setaffinity(&tid, cpumask + cpumasksize, cpumask, cpumasksize);
+  ASSERT_OK(r);
+}
+
+
+TEST_IMPL(thread_affinity) {
+  int t1first;
+  int t1second;
+  int t2first;
+  int t2second;
+  int cpumasksize;
+  char* cpumask;
+  int ncpus;
+  int r;
+  int c;
+  int i;
+  uv_thread_t threads[3];
+
+#ifdef _WIN32
+  /* uv_thread_self isn't defined for the main thread on Windows */
+  threads[0] = GetCurrentThread();
+#else
+  threads[0] = uv_thread_self();
+#endif
+  cpumasksize = uv_cpumask_size();
+  ASSERT_GT(cpumasksize, 0);
+
+  cpumask = calloc(4 * cpumasksize, 1);
+  ASSERT(cpumask);
+
+  r = uv_thread_getaffinity(&threads[0], cpumask, cpumasksize);
+  ASSERT_OK(r);
+  ASSERT(cpumask[0] && "test must be run with cpu 0 affinity");
+  ncpus = 0;
+  while (cpumask[++ncpus]) { }
+  memset(cpumask, 0, 4 * cpumasksize);
+
+  t1first = cpumasksize * 0;
+  t1second = cpumasksize * 1;
+  t2first = cpumasksize * 2;
+  t2second = cpumasksize * 3;
+
+  cpumask[t1second + 0] = 1;
+  cpumask[t2first + 0] = 1;
+  cpumask[t1first + (ncpus >= 2)] = 1;
+  cpumask[t2second + (ncpus >= 2)] = 1;
+#ifdef __linux__
+  cpumask[t1second + 2] = 1;
+  cpumask[t2first + 2] = 1;
+  cpumask[t1first + 3] = 1;
+  cpumask[t2second + 3] = 1;
+#else
+  if (ncpus >= 3) {
+    cpumask[t1second + 2] = 1;
+    cpumask[t2first + 2] = 1;
+  }
+  if (ncpus >= 4) {
+    cpumask[t1first + 3] = 1;
+    cpumask[t2second + 3] = 1;
+  }
+#endif
+
+  ASSERT_OK(uv_thread_create(threads + 1,
+                             check_affinity,
+                             &cpumask[t1first]));
+  ASSERT_OK(uv_thread_create(threads + 2,
+                             check_affinity,
+                             &cpumask[t2first]));
+  ASSERT_OK(uv_thread_join(threads + 1));
+  ASSERT_OK(uv_thread_join(threads + 2));
+
+  ASSERT(cpumask[t1first + 0] == (ncpus == 1));
+  ASSERT(cpumask[t1first + 1] == (ncpus >= 2));
+  ASSERT_OK(cpumask[t1first + 2]);
+  ASSERT(cpumask[t1first + 3] == (ncpus >= 4));
+
+  ASSERT_EQ(1, cpumask[t2first + 0]);
+  ASSERT_OK(cpumask[t2first + 1]);
+  ASSERT(cpumask[t2first + 2] == (ncpus >= 3));
+  ASSERT_OK(cpumask[t2first + 3]);
+
+  c = uv_thread_getcpu();
+  ASSERT_GE(c, 0);
+
+  memset(cpumask, 0, cpumasksize);
+  cpumask[c] = 1;
+  r = uv_thread_setaffinity(&threads[0], cpumask, NULL, cpumasksize);
+  ASSERT_OK(r);
+
+  memset(cpumask, 0, cpumasksize);
+  r = uv_thread_getaffinity(&threads[0], cpumask, cpumasksize);
+  ASSERT_OK(r);
+  for (i = 0; i < cpumasksize; i++) {
+    if (i == c)
+      ASSERT_EQ(1, cpumask[i]);
+    else
+      ASSERT_OK(cpumask[i]);
+  }
+
+  free(cpumask);
+
+  return 0;
+}
+
+#else
+
+TEST_IMPL(thread_affinity) {
+  int cpumasksize;
+  cpumasksize = uv_cpumask_size();
+  ASSERT_EQ(cpumasksize, UV_ENOTSUP);
+  return 0;
+}
+
+#endif