gh-138004: Encode thread names on Solaris-based platforms as ASCII and fix main/worker threading test

Lib/test/test_threading.py

@@ -2358,10 +2358,17 @@ def work():
             with self.subTest(name=name, expected=expected):
                 work_name = None
                 thread = threading.Thread(target=work, name=name)
-                thread.start()
-                thread.join()
-                self.assertEqual(work_name, expected,
-                                 f"{len(work_name)=} and {len(expected)=}")
+                try:
+                    thread.start()
+                    thread.join()
+                    self.assertEqual(work_name, expected,
+                                     f"{len(work_name)=} and {len(expected)=}")
+                except OSError as exc:
+                    # Accept EINVAL (22) for non-ASCII names on platforms that do not support them
+                    if getattr(exc, 'errno', None) == 22 and any(ord(c) > 127 for c in name):
+                        self.skipTest(f"Platform does not support non-ASCII thread names: {exc}")
+                    else:
+                        raise
 
     @unittest.skipUnless(hasattr(_thread, 'set_name'), "missing _thread.set_name")
     @unittest.skipUnless(hasattr(_thread, '_get_name'), "missing _thread._get_name")

Misc/ACKS

@@ -483,6 +483,7 @@ Weilin Du
 John DuBois
 Paul Dubois
 Jacques Ducasse
+Jadon Duff
 Andrei Dorian Duma
 Graham Dumpleton
 Quinn Dunkan

Misc/NEWS.d/next/Core_and_Builtins/2025-08-21-06-31-42.gh-issue-138004.FH2Hre.rst

@@ -0,0 +1,7 @@
+```
+Core and Builtins
+-----------------
+
+* _thread.set_name() now retries with an ASCII fallback if pthread_setname_np() rejects UTF-8 names on some platforms (e.g. OpenIndiana).
+* test_threading.py was updated to skip non-ASCII thread name tests on platforms that do not support them.
+```

Modules/_threadmodule.c

@@ -2611,20 +2611,57 @@ _thread_set_name_impl(PyObject *module, PyObject *name_obj)
 #endif
 
     const char *name = PyBytes_AS_STRING(name_encoded);
+    int rc;
 #ifdef __APPLE__
-    int rc = pthread_setname_np(name);
+    rc = pthread_setname_np(name);
 #elif defined(__NetBSD__)
     pthread_t thread = pthread_self();
-    int rc = pthread_setname_np(thread, "%s", (void *)name);
+    rc = pthread_setname_np(thread, "%s", (void *)name);
 #elif defined(HAVE_PTHREAD_SETNAME_NP)
     pthread_t thread = pthread_self();
-    int rc = pthread_setname_np(thread, name);
+    rc = pthread_setname_np(thread, name);
 #else /* defined(HAVE_PTHREAD_SET_NAME_NP) */
     pthread_t thread = pthread_self();
-    int rc = 0; /* pthread_set_name_np() returns void */
+    rc = 0; /* pthread_set_name_np() returns void */
     pthread_set_name_np(thread, name);
 #endif
     Py_DECREF(name_encoded);
+
+    // Fallback: If EINVAL, try ASCII encoding with "replace"
+    if (rc == EINVAL) {
+        name_encoded = PyUnicode_AsEncodedString(name_obj, "ascii", "replace");
+        if (name_encoded == NULL) {
+            return NULL;
+        }
+#ifdef _PYTHREAD_NAME_MAXLEN
+        if (PyBytes_GET_SIZE(name_encoded) > _PYTHREAD_NAME_MAXLEN) {
+            PyObject *truncated;
+            truncated = PyBytes_FromStringAndSize(PyBytes_AS_STRING(name_encoded),
+                                                  _PYTHREAD_NAME_MAXLEN);
+            if (truncated == NULL) {
+                Py_DECREF(name_encoded);
+                return NULL;
+            }
+            Py_SETREF(name_encoded, truncated);
+        }
+#endif
+        name = PyBytes_AS_STRING(name_encoded);
+#ifdef __APPLE__
+        rc = pthread_setname_np(name);
+#elif defined(__NetBSD__)
+        thread = pthread_self();
+        rc = pthread_setname_np(thread, "%s", (void *)name);
+#elif defined(HAVE_PTHREAD_SETNAME_NP)
+        thread = pthread_self();
+        rc = pthread_setname_np(thread, name);
+#else /* defined(HAVE_PTHREAD_SET_NAME_NP) */
+        thread = pthread_self();
+        rc = 0;
+        pthread_set_name_np(thread, name);
+#endif
+        Py_DECREF(name_encoded);
+    }
+
     if (rc) {
         errno = rc;
         return PyErr_SetFromErrno(PyExc_OSError);