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>

2 files changed, 69 insertions, 0 deletions

diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index fe22555..d05161f 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -2104,6 +2104,66 @@ class MiscTestCase(unittest.TestCase):
         support.check__all__(self, threading, ('threading', '_thread'),
                              extra=extra, not_exported=not_exported)
 
+    @unittest.skipUnless(hasattr(_thread, 'set_name'), "missing _thread.set_name")
+    @unittest.skipUnless(hasattr(_thread, '_get_name'), "missing _thread._get_name")
+    def test_set_name(self):
+        # set_name() limit in bytes
+        truncate = getattr(_thread, "_NAME_MAXLEN", None)
+        limit = truncate or 100
+
+        tests = [
+            # test short ASCII name
+            "CustomName",
+
+            # test short non-ASCII name
+            "namé€",
+
+            # embedded null character: name is truncated
+            # at the first null character
+            "embed\0null",
+
+            # Test long ASCII names (not truncated)
+            "x" * limit,
+
+            # Test long ASCII names (truncated)
+            "x" * (limit + 10),
+
+            # Test long non-ASCII name (truncated)
+            "x" * (limit - 1) + "é€",
+        ]
+        if os_helper.FS_NONASCII:
+            tests.append(f"nonascii:{os_helper.FS_NONASCII}")
+        if os_helper.TESTFN_UNENCODABLE:
+            tests.append(os_helper.TESTFN_UNENCODABLE)
+
+        if sys.platform.startswith("solaris"):
+            encoding = "utf-8"
+        else:
+            encoding = sys.getfilesystemencoding()
+
+        def work():
+            nonlocal work_name
+            work_name = _thread._get_name()
+
+        for name in tests:
+            encoded = name.encode(encoding, "replace")
+            if b'\0' in encoded:
+                encoded = encoded.split(b'\0', 1)[0]
+            if truncate is not None:
+                encoded = encoded[:truncate]
+            if sys.platform.startswith("solaris"):
+                expected = encoded.decode("utf-8", "surrogateescape")
+            else:
+                expected = os.fsdecode(encoded)
+
+            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)=}")
+
 
 class InterruptMainTests(unittest.TestCase):
     def check_interrupt_main_with_signal_handler(self, signum):
diff --git a/Lib/threading.py b/Lib/threading.py
index 94ea2f0..3abd22a 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -48,6 +48,10 @@ try:
     __all__.append('get_native_id')
 except AttributeError:
     _HAVE_THREAD_NATIVE_ID = False
+try:
+    _set_name = _thread.set_name
+except AttributeError:
+    _set_name = None
 ThreadError = _thread.error
 try:
     _CRLock = _thread.RLock
@@ -1027,6 +1031,11 @@ class Thread:
             self._set_ident()
             if _HAVE_THREAD_NATIVE_ID:
                 self._set_native_id()
+            if _set_name is not None and self._name:
+                try:
+                    _set_name(self._name)
+                except OSError:
+                    pass
             self._started.set()
             with _active_limbo_lock:
                 _active[self._ident] = self