python · miss-islington · Oct 11, 2020 · Apr 28, 2020 · Apr 27, 2020 · Oct 10, 2020
diff --git a/Misc/NEWS.d/next/C API/2020-10-10-14-05-24.bpo-40422.sh8IDY.rst b/Misc/NEWS.d/next/C API/2020-10-10-14-05-24.bpo-40422.sh8IDY.rst
@@ -0,0 +1 @@
+Add `_Py_closerange` function to provide performant closing of a range of file descriptors.
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
@@ -250,29 +250,18 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_fds_to_keep)
     long end_fd = safe_get_max_fd();
     Py_ssize_t num_fds_to_keep = PyTuple_GET_SIZE(py_fds_to_keep);
     Py_ssize_t keep_seq_idx;
-    int fd_num;
     /* As py_fds_to_keep is sorted we can loop through the list closing
      * fds in between any in the keep list falling within our range. */
     for (keep_seq_idx = 0; keep_seq_idx < num_fds_to_keep; ++keep_seq_idx) {
         PyObject* py_keep_fd = PyTuple_GET_ITEM(py_fds_to_keep, keep_seq_idx);
         int keep_fd = PyLong_AsLong(py_keep_fd);
         if (keep_fd < start_fd)
             continue;
-        for (fd_num = start_fd; fd_num < keep_fd; ++fd_num) {
-            close(fd_num);
-        }
+        _Py_closerange(start_fd, keep_fd - 1);
         start_fd = keep_fd + 1;
     }
     if (start_fd <= end_fd) {
-#if defined(__FreeBSD__)
-        /* Any errors encountered while closing file descriptors are ignored */
-        closefrom(start_fd);
-#else
-        for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
-            /* Ignore errors */
-            (void)close(fd_num);
-        }
-#endif
+        _Py_closerange(start_fd, end_fd);
     }
 }
 

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
@@ -8740,8 +8740,23 @@ os_close_impl(PyObject *module, int fd)
     Py_RETURN_NONE;
 }
 
+/* Our selection logic for which function to use is as follows:
+ * 1. If closefrom(2) is available, we'll attempt to use that next if we're
+ *    closing up to sysconf(_SC_OPEN_MAX).
+ * 1a. Fallback to fdwalk(3) if we're not closing up to sysconf(_SC_OPEN_MAX),
+ *    as that will be more performant if the range happens to have any chunk of
+ *    non-opened fd in the middle.
+ * 1b. If fdwalk(3) isn't available, just do a plain close(2) loop.
+ */
+#ifdef __FreeBSD__
+#define USE_CLOSEFROM
+#endif /* __FreeBSD__ */
 
 #ifdef HAVE_FDWALK
+#define USE_FDWALK
+#endif /* HAVE_FDWALK */
+
+#ifdef USE_FDWALK
 static int
 _fdwalk_close_func(void *lohi, int fd)
 {
@@ -8757,7 +8772,36 @@ _fdwalk_close_func(void *lohi, int fd)
     }
     return 0;
 }
-#endif /* HAVE_FDWALK */
+#endif /* USE_FDWALK */
+
+/* Closes all file descriptors in [first, last], ignoring errors. */
+void
+_Py_closerange(int first, int last)
+{
+    first = Py_MAX(first, 0);
+#ifdef USE_CLOSEFROM
+    if (last >= sysconf(_SC_OPEN_MAX)) {
+        /* Any errors encountered while closing file descriptors are ignored */
+        closefrom(first);
+    }
+    else
+#endif /* USE_CLOSEFROM */
+#ifdef USE_FDWALK
+    {
+        int lohi[2];
+        lohi[0] = first;
+        lohi[1] = last + 1;
+        fdwalk(_fdwalk_close_func, lohi);
+    }
+#else
+    {
+        for (int i = first; i <= last; i++) {
+            /* Ignore errors */
+            (void)close(i);
+        }
+    }
+#endif /* USE_FDWALK */
+}
 
 /*[clinic input]
 os.closerange
@@ -8773,31 +8817,9 @@ static PyObject *
 os_closerange_impl(PyObject *module, int fd_low, int fd_high)
 /*[clinic end generated code: output=0ce5c20fcda681c2 input=5855a3d053ebd4ec]*/
 {
-#ifdef HAVE_FDWALK
-    int lohi[2];
-#endif
     Py_BEGIN_ALLOW_THREADS
     _Py_BEGIN_SUPPRESS_IPH
-#ifdef HAVE_FDWALK
-    lohi[0] = Py_MAX(fd_low, 0);
-    lohi[1] = fd_high;
-    fdwalk(_fdwalk_close_func, lohi);
-#else
-    fd_low = Py_MAX(fd_low, 0);
-#ifdef __FreeBSD__
-    if (fd_high >= sysconf(_SC_OPEN_MAX)) {
-        /* Any errors encountered while closing file descriptors are ignored */
-        closefrom(fd_low);
-    }
-    else
-#endif
-    {
-        for (int i = fd_low; i < fd_high; i++) {
-            /* Ignore errors */
-            (void)close(i);
-        }
-    }
-#endif
+    _Py_closerange(fd_low, fd_high - 1);
     _Py_END_SUPPRESS_IPH
     Py_END_ALLOW_THREADS
     Py_RETURN_NONE;

diff --git a/Modules/posixmodule.h b/Modules/posixmodule.h
@@ -28,6 +28,8 @@ PyAPI_FUNC(int) _Py_Sigset_Converter(PyObject *, void *);
 #endif /* HAVE_SIGSET_T */
 #endif /* Py_LIMITED_API */
 
+PyAPI_FUNC(void) _Py_closerange(int first, int last);
+
 #ifdef __cplusplus
 }
 #endif
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Add `_Py_closerange` function to provide performant closing of a range of file descriptors.