Address review iteration 2: whatsnew entry + Py_ssize_t

- Add a 'faulthandler' entry to Doc/whatsnew/3.15.rst (per
  @ZeroIntensity).
- Switch the max_threads parameters/fields and the nthreads loop
  counter in _Py_DumpTracebackThreads to Py_ssize_t (per @vstinner).

Author: efroemling

Doc/whatsnew/3.15.rst

@@ -894,6 +894,14 @@ difflib
   (Contributed by Jiahao Li in :gh:`134580`.)
 
 
+faulthandler
+------------
+
+* Added the *max_threads* parameter in :func:`faulthandler.enable`,
+  :func:`faulthandler.dump_traceback`, and :func:`faulthandler.dump_traceback_later`.
+  (Contributed by Eric Froemling in :gh:`149085`.)
+
+
 functools
 ---------
 

Include/internal/pycore_faulthandler.h

@@ -57,7 +57,7 @@ struct _faulthandler_runtime_state {
         void *exc_handler;
 #endif
         int c_stack;
-        unsigned int max_threads;
+        Py_ssize_t max_threads;
     } fatal_error;
 
     struct {
@@ -69,7 +69,7 @@ struct _faulthandler_runtime_state {
         int exit;
         char *header;
         size_t header_len;
-        unsigned int max_threads;
+        Py_ssize_t max_threads;
         /* The main thread always holds this lock. It is only released when
            faulthandler_thread() is interrupted before this thread exits, or at
            Python exit. */

Include/internal/pycore_traceback.h

@@ -62,7 +62,7 @@ extern const char* _Py_DumpTracebackThreads(
     int fd,
     PyInterpreterState *interp,
     PyThreadState *current_tstate,
-    unsigned int max_threads);
+    Py_ssize_t max_threads);
 
 /* Write a Unicode object into the file descriptor fd. Encode the string to
    ASCII using the backslashreplace error handler.

Modules/clinic/faulthandler.c.h

@@ -186,7 +186,7 @@ get_thread_state(void)
 static void
 faulthandler_dump_traceback(int fd, int all_threads,
                             PyInterpreterState *interp,
-                            unsigned int max_threads)
+                            Py_ssize_t max_threads)
 {
     static volatile int reentrant = 0;
 
@@ -245,7 +245,7 @@ faulthandler.dump_traceback as faulthandler_dump_traceback_py
     file: object(py_default="sys.stderr") = NULL
     all_threads: bool = True
     *
-    max_threads: unsigned_int(bitwise=False) = 100
+    max_threads: Py_ssize_t = 100
 
 Dump the traceback of the current thread into file.
 
@@ -255,9 +255,8 @@ caps the number of threads dumped.
 
 static PyObject *
 faulthandler_dump_traceback_py_impl(PyObject *module, PyObject *file,
-                                    int all_threads,
-                                    unsigned int max_threads)
-/*[clinic end generated code: output=e2b1d5c6bb275cb5 input=3f84b644d7b226a6]*/
+                                    int all_threads, Py_ssize_t max_threads)
+/*[clinic end generated code: output=ee1bbc2668e56e77 input=38630eb40e641de6]*/
 {
     PyThreadState *tstate;
     const char *errmsg;
@@ -598,16 +597,16 @@ faulthandler.enable as faulthandler_py_enable
     all_threads: bool = True
     c_stack: bool = True
     *
-    max_threads: unsigned_int(bitwise=False) = 100
+    max_threads: Py_ssize_t = 100
 
 Enable the fault handler.
 [clinic start generated code]*/
 
 static PyObject *
 faulthandler_py_enable_impl(PyObject *module, PyObject *file,
                             int all_threads, int c_stack,
-                            unsigned int max_threads)
-/*[clinic end generated code: output=5050dceeeeda70a4 input=e2607dfbb2c7f4ac]*/
+                            Py_ssize_t max_threads)
+/*[clinic end generated code: output=7ee655332317c47a input=e64759714f27b466]*/
 {
     int fd;
     PyThreadState *tstate;
@@ -790,7 +789,7 @@ faulthandler.dump_traceback_later
     file: object(py_default="sys.stderr") = NULL
     exit: bool = False
     *
-    max_threads: unsigned_int(bitwise=False) = 100
+    max_threads: Py_ssize_t = 100
 
 Dump the traceback of all threads in timeout seconds.
 
@@ -803,8 +802,8 @@ static PyObject *
 faulthandler_dump_traceback_later_impl(PyObject *module,
                                        PyObject *timeout_obj, int repeat,
                                        PyObject *file, int exit,
-                                       unsigned int max_threads)
-/*[clinic end generated code: output=a0a1551011fe9f5f input=9aabfe7079a05dd3]*/
+                                       Py_ssize_t max_threads)
+/*[clinic end generated code: output=543a0f3807113394 input=6836555ee157ddb4]*/
 {
     PyTime_t timeout, timeout_us;
     int fd;

Modules/faulthandler.c

@@ -1266,7 +1266,7 @@ write_thread_id(int fd, PyThreadState *tstate, int is_current)
 const char* _Py_NO_SANITIZE_THREAD
 _Py_DumpTracebackThreads(int fd, PyInterpreterState *interp,
                          PyThreadState *current_tstate,
-                         unsigned int max_threads)
+                         Py_ssize_t max_threads)
 {
     if (max_threads == 0) {
         max_threads = DEFAULT_MAX_NTHREADS;
@@ -1315,7 +1315,7 @@ _Py_DumpTracebackThreads(int fd, PyInterpreterState *interp,
         return "unable to get the thread head state";
 
     /* Dump the traceback of each thread */
-    unsigned int nthreads = 0;
+    Py_ssize_t nthreads = 0;
     _Py_BEGIN_SUPPRESS_IPH
     do
     {