gh-125434: Display thread name in faulthandler on Windows (#140675)

Author: vstinner

Include/internal/pycore_traceback.h

@@ -103,6 +103,8 @@ extern int _Py_WriteIndent(int, PyObject *);
 PyAPI_FUNC(void) _Py_InitDumpStack(void);
 PyAPI_FUNC(void) _Py_DumpStack(int fd);
 
+extern void _Py_DumpTraceback_Init(void);
+
 #ifdef __cplusplus
 }
 #endif

Misc/NEWS.d/next/Library/2025-10-27-16-01-41.gh-issue-125434.qy0uRA.rst

@@ -0,0 +1,2 @@
+Display thread name in :mod:`faulthandler` on Windows. Patch by Victor
+Stinner.

Python/pylifecycle.c

@@ -506,6 +506,7 @@ pycore_init_runtime(_PyRuntimeState *runtime,
     _PyRuntimeState_SetFinalizing(runtime, NULL);
 
     _Py_InitVersion();
+    _Py_DumpTraceback_Init();
 
     status = _Py_HashRandomization_Init(config);
     if (_PyStatus_EXCEPTION(status)) {

Python/traceback.c

@@ -69,6 +69,13 @@ class traceback "PyTracebackObject *" "&PyTraceback_Type"
 
 #include "clinic/traceback.c.h"
 
+
+#ifdef MS_WINDOWS
+typedef HRESULT (WINAPI *PF_GET_THREAD_DESCRIPTION)(HANDLE, PCWSTR*);
+static PF_GET_THREAD_DESCRIPTION pGetThreadDescription = NULL;
+#endif
+
+
 static PyObject *
 tb_create_raw(PyTracebackObject *next, PyFrameObject *frame, int lasti,
               int lineno)
@@ -1107,23 +1114,12 @@ _Py_DumpTraceback(int fd, PyThreadState *tstate)
 # endif
 #endif
 
-/* Write the thread identifier into the file 'fd': "Current thread 0xHHHH:\" if
-   is_current is true, "Thread 0xHHHH:\n" otherwise.
-
-   This function is signal safe. */
 
+// Write the thread name
 static void
-write_thread_id(int fd, PyThreadState *tstate, int is_current)
+write_thread_name(int fd, PyThreadState *tstate)
 {
-    if (is_current)
-        PUTS(fd, "Current thread 0x");
-    else
-        PUTS(fd, "Thread 0x");
-    _Py_DumpHexadecimal(fd,
-                        tstate->thread_id,
-                        sizeof(unsigned long) * 2);
-
-    // Write the thread name
+#ifndef MS_WINDOWS
 #if defined(HAVE_PTHREAD_GETNAME_NP) || defined(HAVE_PTHREAD_GET_NAME_NP)
     char name[100];
     pthread_t thread = (pthread_t)tstate->thread_id;
@@ -1142,6 +1138,54 @@ write_thread_id(int fd, PyThreadState *tstate, int is_current)
         }
     }
 #endif
+#else
+    // Windows implementation
+    if (pGetThreadDescription == NULL) {
+        return;
+    }
+
+    HANDLE thread = OpenThread(THREAD_QUERY_LIMITED_INFORMATION, FALSE, tstate->thread_id);
+    if (thread == NULL) {
+        return;
+    }
+
+    wchar_t *wname;
+    HRESULT hr = pGetThreadDescription(thread, &wname);
+    if (!FAILED(hr)) {
+        char *name = _Py_EncodeLocaleRaw(wname, NULL);
+        if (name != NULL) {
+            size_t len = strlen(name);
+            if (len) {
+                PUTS(fd, " [");
+                (void)_Py_write_noraise(fd, name, len);
+                PUTS(fd, "]");
+            }
+            PyMem_RawFree(name);
+        }
+        LocalFree(wname);
+    }
+    CloseHandle(thread);
+#endif
+}
+
+
+/* Write the thread identifier into the file 'fd': "Current thread 0xHHHH:\" if
+   is_current is true, "Thread 0xHHHH:\n" otherwise.
+
+   This function is signal safe (except on Windows). */
+
+static void
+write_thread_id(int fd, PyThreadState *tstate, int is_current)
+{
+    if (is_current)
+        PUTS(fd, "Current thread 0x");
+    else
+        PUTS(fd, "Thread 0x");
+    _Py_DumpHexadecimal(fd,
+                        tstate->thread_id,
+                        sizeof(unsigned long) * 2);
+
+    write_thread_name(fd, tstate);
 
     PUTS(fd, " (most recent call first):\n");
 }
@@ -1336,3 +1380,20 @@ _Py_InitDumpStack(void)
     (void)backtrace(callstack, 1);
 #endif
 }
+
+
+void
+_Py_DumpTraceback_Init(void)
+{
+#ifdef MS_WINDOWS
+    if (pGetThreadDescription != NULL) {
+        return;
+    }
+
+    HMODULE kernelbase = GetModuleHandleW(L"kernelbase.dll");
+    if (kernelbase != NULL) {
+        pGetThreadDescription = (PF_GET_THREAD_DESCRIPTION)GetProcAddress(
+                                    kernelbase, "GetThreadDescription");
+    }
+#endif
+}