gh-59705: Add _thread.set_name() function (#127338)

On Linux, threading.Thread now sets the thread name to the operating
system.

* configure now checks if pthread_getname_np()
  and pthread_setname_np() functions are available.
* Add PYTHREAD_NAME_MAXLEN macro.
* Add _thread._NAME_MAXLEN constant for test_threading.

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Modules/_threadmodule.c

@@ -17,6 +17,8 @@
 #  include <signal.h>             // SIGINT
 #endif
 
+#include "clinic/_threadmodule.c.h"
+
 // ThreadError is just an alias to PyExc_RuntimeError
 #define ThreadError PyExc_RuntimeError
 
@@ -44,6 +46,13 @@ get_thread_state(PyObject *module)
     return (thread_module_state *)state;
 }
 
+
+/*[clinic input]
+module _thread
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=be8dbe5cc4b16df7]*/
+
+
 // _ThreadHandle type
 
 // Handles state transitions according to the following diagram:
@@ -2354,6 +2363,96 @@ PyDoc_STRVAR(thread__get_main_thread_ident_doc,
 Internal only. Return a non-zero integer that uniquely identifies the main thread\n\
 of the main interpreter.");
 
+
+#ifdef HAVE_PTHREAD_GETNAME_NP
+/*[clinic input]
+_thread._get_name
+
+Get the name of the current thread.
+[clinic start generated code]*/
+
+static PyObject *
+_thread__get_name_impl(PyObject *module)
+/*[clinic end generated code: output=20026e7ee3da3dd7 input=35cec676833d04c8]*/
+{
+    // Linux and macOS are limited to respectively 16 and 64 bytes
+    char name[100];
+    pthread_t thread = pthread_self();
+    int rc = pthread_getname_np(thread, name, Py_ARRAY_LENGTH(name));
+    if (rc) {
+        errno = rc;
+        return PyErr_SetFromErrno(PyExc_OSError);
+    }
+
+#ifdef __sun
+    return PyUnicode_DecodeUTF8(name, strlen(name), "surrogateescape");
+#else
+    return PyUnicode_DecodeFSDefault(name);
+#endif
+}
+#endif  // HAVE_PTHREAD_GETNAME_NP
+
+
+#ifdef HAVE_PTHREAD_SETNAME_NP
+/*[clinic input]
+_thread.set_name
+
+    name as name_obj: unicode
+
+Set the name of the current thread.
+[clinic start generated code]*/
+
+static PyObject *
+_thread_set_name_impl(PyObject *module, PyObject *name_obj)
+/*[clinic end generated code: output=402b0c68e0c0daed input=7e7acd98261be82f]*/
+{
+#ifdef __sun
+    // Solaris always uses UTF-8
+    const char *encoding = "utf-8";
+#else
+    // Encode the thread name to the filesystem encoding using the "replace"
+    // error handler
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    const char *encoding = interp->unicode.fs_codec.encoding;
+#endif
+    PyObject *name_encoded;
+    name_encoded = PyUnicode_AsEncodedString(name_obj, encoding, "replace");
+    if (name_encoded == NULL) {
+        return NULL;
+    }
+
+#ifdef PYTHREAD_NAME_MAXLEN
+    // Truncate to PYTHREAD_NAME_MAXLEN bytes + the NUL byte if needed
+    size_t len = PyBytes_GET_SIZE(name_encoded);
+    if (len > 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
+
+    const char *name = PyBytes_AS_STRING(name_encoded);
+#ifdef __APPLE__
+    int rc = pthread_setname_np(name);
+#else
+    pthread_t thread = pthread_self();
+    int rc = pthread_setname_np(thread, name);
+#endif
+    Py_DECREF(name_encoded);
+    if (rc) {
+        errno = rc;
+        return PyErr_SetFromErrno(PyExc_OSError);
+    }
+    Py_RETURN_NONE;
+}
+#endif  // HAVE_PTHREAD_SETNAME_NP
+
+
 static PyMethodDef thread_methods[] = {
     {"start_new_thread",        (PyCFunction)thread_PyThread_start_new_thread,
      METH_VARARGS, start_new_thread_doc},
@@ -2393,6 +2492,8 @@ static PyMethodDef thread_methods[] = {
      METH_O, thread__make_thread_handle_doc},
     {"_get_main_thread_ident", thread__get_main_thread_ident,
      METH_NOARGS, thread__get_main_thread_ident_doc},
+    _THREAD_SET_NAME_METHODDEF
+    _THREAD__GET_NAME_METHODDEF
     {NULL,                      NULL}           /* sentinel */
 };
 
@@ -2484,6 +2585,13 @@ thread_module_exec(PyObject *module)
 
     llist_init(&state->shutdown_handles);
 
+#ifdef PYTHREAD_NAME_MAXLEN
+    if (PyModule_AddIntConstant(module, "_NAME_MAXLEN",
+                                PYTHREAD_NAME_MAXLEN) < 0) {
+        return -1;
+    }
+#endif
+
     return 0;
 }