commit 23c46778d65870784cb6d4de30f43aac62d71e73
author Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Thu Sep 09 09:35:43 2021 -0700
committer GitHub <noreply@github.com> Thu Sep 09 18:35:43 2021 +0200
tree 3c359476d5179bbbf8843d43b1b9d8c08ad5238e
parent 11103eb1f2199cacd8c2e29e3db0d19199885b45

bpo-44219: Release the GIL during isatty syscalls (GH-28250) (GH-28255)

Release the GIL while performing isatty() system calls on arbitrary
file descriptors. In particular, this affects os.isatty(),
os.device_encoding() and io.TextIOWrapper. By extension,
io.open() in text mode is also affected.
(cherry picked from commit 06148b1870fceb1a21738761b8e1ac3bf654319b)

Co-authored-by: Vincent Michel <vxgmichel@gmail.com>

Python/fileutils.c

diff --git a/Python/fileutils.c b/Python/fileutils.c
index e8a7eda..9e732dd 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -67,9 +67,11 @@ PyObject *
 _Py_device_encoding(int fd)
 {
     int valid;
+    Py_BEGIN_ALLOW_THREADS
     _Py_BEGIN_SUPPRESS_IPH
     valid = isatty(fd);
     _Py_END_SUPPRESS_IPH
+    Py_END_ALLOW_THREADS
     if (!valid)
         Py_RETURN_NONE;
 
@@ -1776,12 +1778,22 @@ _Py_write_impl(int fd, const void *buf, size_t count, int gil_held)
 
     _Py_BEGIN_SUPPRESS_IPH
 #ifdef MS_WINDOWS
-    if (count > 32767 && isatty(fd)) {
+    if (count > 32767) {
         /* Issue #11395: the Windows console returns an error (12: not
            enough space error) on writing into stdout if stdout mode is
            binary and the length is greater than 66,000 bytes (or less,
            depending on heap usage). */
-        count = 32767;
+        if (gil_held) {
+            Py_BEGIN_ALLOW_THREADS
+            if (isatty(fd)) {
+                count = 32767;
+            }
+            Py_END_ALLOW_THREADS
+        } else {
+            if (isatty(fd)) {
+                count = 32767;
+            }
+        }
     }
 #endif
     if (count > _PY_WRITE_MAX) {