gh-142434: Use ppoll() if available in select.poll

Author: vstinner

Doc/library/select.rst

@@ -478,6 +478,8 @@ linearly scanned again. :c:func:`!select` is *O*\ (*highest file descriptor*), w
 
    .. versionchanged:: 3.15
       Accepts any real number as *timeout*, not only integer or float.
+      If ``ppoll()`` function is available, *timeout* has a resolution
+      of ``1`` ns (``1e-6`` ms) instead of ``1`` ms.
 
 
 .. _kqueue-objects:

Lib/test/test_poll.py

@@ -173,17 +173,25 @@ def test_poll3(self):
     @cpython_only
     def test_poll_c_limits(self):
         try:
+            import _testcapi
             from _testcapi import USHRT_MAX, INT_MAX, UINT_MAX
+            HAVE_PPOLL = getattr(_testcapi, 'HAVE_PPOLL', False)
         except ImportError:
             raise unittest.SkipTest("requires _testcapi")
+
         pollster = select.poll()
         pollster.register(1)
 
         # Issues #15989, #17919
         self.assertRaises(OverflowError, pollster.register, 0, USHRT_MAX + 1)
         self.assertRaises(OverflowError, pollster.modify, 1, USHRT_MAX + 1)
-        self.assertRaises(OverflowError, pollster.poll, INT_MAX + 1)
-        self.assertRaises(OverflowError, pollster.poll, UINT_MAX + 1)
+        if HAVE_PPOLL:
+            MS_TO_NS = 1_000_000
+            tmax = _testcapi.INT64_MAX // MS_TO_NS
+            self.assertRaises(OverflowError, pollster.poll, tmax + 1)
+        else:
+            self.assertRaises(OverflowError, pollster.poll, INT_MAX + 1)
+            self.assertRaises(OverflowError, pollster.poll, UINT_MAX + 1)
 
     @threading_helper.reap_threads
     def test_threaded_poll(self):

Misc/NEWS.d/next/Library/2026-01-07-19-01-59.gh-issue-142434.SHRS5p.rst

@@ -0,0 +1,3 @@
+Use ``ppoll()`` if available in :func:`select.poll` to have a timeout
+resolution of 1 nanosecond, instead of a resolution of 1 ms. Patch by Victor
+Stinner.

Modules/_testcapimodule.c

@@ -3359,6 +3359,12 @@ _testcapi_exec(PyObject *m)
     PyModule_AddObject(m, "INT64_MAX", PyLong_FromInt64(INT64_MAX));
     PyModule_AddObject(m, "UINT64_MAX", PyLong_FromUInt64(UINT64_MAX));
 
+#ifdef HAVE_PPOLL
+    if (PyModule_AddObjectRef(m, "HAVE_PPOLL", Py_True) < 0) {
+        return -1;
+    }
+#endif
+
     if (PyModule_AddIntMacro(m, _Py_STACK_GROWS_DOWN)) {
         return -1;
     }

Modules/selectmodule.c

@@ -427,7 +427,7 @@ select_select_impl(PyObject *module, PyObject *rlist, PyObject *wlist,
     return ret;
 }
 
-#if defined(HAVE_POLL) && !defined(HAVE_BROKEN_POLL)
+#if (defined(HAVE_POLL) || defined(HAVE_PPOLL)) && !defined(HAVE_BROKEN_POLL)
 /*
  * poll() support
  */
@@ -626,7 +626,7 @@ select_poll_poll_impl(pollObject *self, PyObject *timeout_obj)
     PyObject *result_list = NULL;
     int poll_result, i, j;
     PyObject *value = NULL, *num = NULL;
-    PyTime_t timeout = -1, ms = -1, deadline = 0;
+    PyTime_t timeout = -1, deadline = 0;
     int async_err = 0;
 
     if (timeout_obj != Py_None) {
@@ -639,15 +639,28 @@ select_poll_poll_impl(pollObject *self, PyObject *timeout_obj)
             }
             return NULL;
         }
+    }
 
-        ms = _PyTime_AsMilliseconds(timeout, _PyTime_ROUND_TIMEOUT);
-        if (ms < INT_MIN || ms > INT_MAX) {
-            PyErr_SetString(PyExc_OverflowError, "timeout is too large");
+#ifdef HAVE_PPOLL
+    struct timespec ts, *ts_p = NULL;
+
+    if (timeout_obj != Py_None) {
+        if (_PyTime_AsTimespec(timeout, &ts) < 0) {
             return NULL;
         }
 
         if (timeout >= 0) {
-            deadline = _PyDeadline_Init(timeout);
+            ts_p = &ts;
+        }
+    }
+#else
+    PyTime_t ms = -1;
+
+    if (timeout_obj != Py_None) {
+        ms = _PyTime_AsMilliseconds(timeout, _PyTime_ROUND_TIMEOUT);
+        if (ms < INT_MIN || ms > INT_MAX) {
+            PyErr_SetString(PyExc_OverflowError, "timeout is too large");
+            return NULL;
         }
     }
 
@@ -661,6 +674,11 @@ select_poll_poll_impl(pollObject *self, PyObject *timeout_obj)
         ms = -1;
 #endif
     }
+#endif
+
+    if (timeout >= 0) {
+        deadline = _PyDeadline_Init(timeout);
+    }
 
     /* Avoid concurrent poll() invocation, issue 8865 */
     if (self->poll_running) {
@@ -681,7 +699,11 @@ select_poll_poll_impl(pollObject *self, PyObject *timeout_obj)
     do {
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
+#ifdef HAVE_PPOLL
+        poll_result = ppoll(self->ufds, self->ufd_len, ts_p, NULL);
+#else
         poll_result = poll(self->ufds, self->ufd_len, (int)ms);
+#endif
         Py_END_ALLOW_THREADS
 
         if (errno != EINTR)
@@ -699,8 +721,16 @@ select_poll_poll_impl(pollObject *self, PyObject *timeout_obj)
                 poll_result = 0;
                 break;
             }
+#ifdef HAVE_PPOLL
+            if (_PyTime_AsTimespec(timeout, &ts) < 0) {
+                poll_result = -1;
+                break;
+            }
+            assert(ts_p == &ts);
+#else
             ms = _PyTime_AsMilliseconds(timeout, _PyTime_ROUND_CEILING);
-            /* retry poll() with the recomputed timeout */
+#endif
+            /* retry poll()/ppoll() with the recomputed timeout */
         }
     } while (1);
 
@@ -2466,7 +2496,7 @@ static PyGetSetDef kqueue_queue_getsetlist[] = {
 
 #include "clinic/selectmodule.c.h"
 
-#if defined(HAVE_POLL) && !defined(HAVE_BROKEN_POLL)
+#if (defined(HAVE_POLL) || defined(HAVE_PPOLL)) && !defined(HAVE_BROKEN_POLL)
 
 static PyMethodDef poll_methods[] = {
     SELECT_POLL_REGISTER_METHODDEF
@@ -2661,7 +2691,7 @@ _select_exec(PyObject *m)
     ADD_INT(PIPE_BUF);
 #endif
 
-#if defined(HAVE_POLL) && !defined(HAVE_BROKEN_POLL)
+#if (defined(HAVE_POLL) || defined(HAVE_PPOLL)) && !defined(HAVE_BROKEN_POLL)
 #ifdef __APPLE__
     if (select_have_broken_poll()) {
         if (PyObject_DelAttrString(m, "poll") == -1) {

configure

@@ -5253,7 +5253,7 @@ AC_CHECK_FUNCS([ \
   getspnam getuid getwd grantpt if_nameindex initgroups kill killpg lchown linkat \
   lockf lstat lutimes madvise mbrtowc memrchr mkdirat mkfifo mkfifoat \
   mknod mknodat mktime mmap mremap nice openat opendir pathconf pause pipe \
-  pipe2 plock poll posix_fadvise posix_fallocate posix_openpt posix_spawn posix_spawnp \
+  pipe2 plock poll ppoll posix_fadvise posix_fallocate posix_openpt posix_spawn posix_spawnp \
   posix_spawn_file_actions_addclosefrom_np \
   pread preadv preadv2 process_vm_readv \
   pthread_cond_timedwait_relative_np pthread_condattr_setclock pthread_init \

configure.ac

@@ -979,6 +979,9 @@
    function. */
 #undef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCLOSEFROM_NP
 
+/* Define to 1 if you have the 'ppoll' function. */
+#undef HAVE_PPOLL
+
 /* Define to 1 if you have the 'pread' function. */
 #undef HAVE_PREAD