diff --git a/Lib/pty.py b/Lib/pty.py
index 6571050886bd1d..1d97994abef3c8 100644
--- a/Lib/pty.py
+++ b/Lib/pty.py
@@ -115,12 +115,6 @@ def fork():
# Parent and child process.
return pid, master_fd
-def _writen(fd, data):
- """Write all the data to a descriptor."""
- while data:
- n = os.write(fd, data)
- data = data[n:]
-
def _read(fd):
"""Default read function."""
return os.read(fd, 1024)
@@ -130,9 +124,42 @@ def _copy(master_fd, master_read=_read, stdin_read=_read):
Copies
pty master -> standard output (master_read)
standard input -> pty master (stdin_read)"""
- fds = [master_fd, STDIN_FILENO]
- while fds:
- rfds, _wfds, _xfds = select(fds, [], [])
+ if os.get_blocking(master_fd):
+ # If we write more than tty/ndisc is willing to buffer, we may block
+ # indefinitely. So we set master_fd to non-blocking temporarily during
+ # the copy operation.
+ os.set_blocking(master_fd, False)
+ try:
+ _copy(master_fd, master_read=master_read, stdin_read=stdin_read)
+ finally:
+ # restore blocking mode for backwards compatibility
+ os.set_blocking(master_fd, True)
+ return
+ high_waterlevel = 4096
+ stdin_avail = master_fd != STDIN_FILENO
+ stdout_avail = master_fd != STDOUT_FILENO
+ i_buf = b''
+ o_buf = b''
+ while 1:
+ rfds = []
+ wfds = []
+ if stdin_avail and len(i_buf) < high_waterlevel:
+ rfds.append(STDIN_FILENO)
+ if stdout_avail and len(o_buf) < high_waterlevel:
+ rfds.append(master_fd)
+ if stdout_avail and len(o_buf) > 0:
+ wfds.append(STDOUT_FILENO)
+ if len(i_buf) > 0:
+ wfds.append(master_fd)
+
+ rfds, wfds, _xfds = select(rfds, wfds, [])
+
+ if STDOUT_FILENO in wfds:
+ try:
+ n = os.write(STDOUT_FILENO, o_buf)
+ o_buf = o_buf[n:]
+ except OSError:
+ stdout_avail = False
if master_fd in rfds:
# Some OSes signal EOF by returning an empty byte string,
@@ -144,15 +171,18 @@ def _copy(master_fd, master_read=_read, stdin_read=_read):
if not data: # Reached EOF.
return # Assume the child process has exited and is
# unreachable, so we clean up.
- else:
- os.write(STDOUT_FILENO, data)
+ o_buf += data
+
+ if master_fd in wfds:
+ n = os.write(master_fd, i_buf)
+ i_buf = i_buf[n:]
- if STDIN_FILENO in rfds:
+ if stdin_avail and STDIN_FILENO in rfds:
data = stdin_read(STDIN_FILENO)
if not data:
- fds.remove(STDIN_FILENO)
+ stdin_avail = False
else:
- _writen(master_fd, data)
+ i_buf += data
def spawn(argv, master_read=_read, stdin_read=_read):
"""Create a spawned process."""
diff --git a/Lib/test/test_pty.py b/Lib/test/test_pty.py
index c723bb362c5d87..c9c2b42861c6f4 100644
--- a/Lib/test/test_pty.py
+++ b/Lib/test/test_pty.py
@@ -312,8 +312,8 @@ def setUp(self):
self.orig_pty_waitpid = pty.waitpid
self.fds = [] # A list of file descriptors to close.
self.files = []
- self.select_rfds_lengths = []
- self.select_rfds_results = []
+ self.select_input = []
+ self.select_output = []
self.tcsetattr_mode_setting = None
def tearDown(self):
@@ -350,8 +350,8 @@ def _socketpair(self):
def _mock_select(self, rfds, wfds, xfds):
# This will raise IndexError when no more expected calls exist.
- self.assertEqual(self.select_rfds_lengths.pop(0), len(rfds))
- return self.select_rfds_results.pop(0), [], []
+ self.assertEqual((rfds, wfds, xfds), self.select_input.pop(0))
+ return self.select_output.pop(0)
def _make_mock_fork(self, pid):
def mock_fork():
@@ -374,11 +374,13 @@ def test__copy_to_each(self):
os.write(masters[1], b'from master')
os.write(write_to_stdin_fd, b'from stdin')
- # Expect two select calls, the last one will cause IndexError
+ # Expect three select calls, the last one will cause IndexError
pty.select = self._mock_select
- self.select_rfds_lengths.append(2)
- self.select_rfds_results.append([mock_stdin_fd, masters[0]])
- self.select_rfds_lengths.append(2)
+ self.select_input.append(([mock_stdin_fd, masters[0]], [], []))
+ self.select_output.append(([mock_stdin_fd, masters[0]], [], []))
+ self.select_input.append(([mock_stdin_fd, masters[0]], [mock_stdout_fd, masters[0]], []))
+ self.select_output.append(([], [mock_stdout_fd, masters[0]], []))
+ self.select_input.append(([mock_stdin_fd, masters[0]], [], []))
with self.assertRaises(IndexError):
pty._copy(masters[0])
diff --git a/Misc/ACKS b/Misc/ACKS
index ca92608868f23f..63875ba0e1cc43 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -2044,6 +2044,7 @@ Yuxiao Zeng
Uwe Zessin
Cheng Zhang
George Zhang
+Youfu Zhang
Charlie Zhao
Kai Zhu
Tarek Ziadé
diff --git a/Misc/NEWS.d/next/Library/2022-09-07-09-32-07.gh-issue-96522.t73oqp.rst b/Misc/NEWS.d/next/Library/2022-09-07-09-32-07.gh-issue-96522.t73oqp.rst
new file mode 100644
index 00000000000000..12ed52f97129eb
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-09-07-09-32-07.gh-issue-96522.t73oqp.rst
@@ -0,0 +1 @@
+Fix potential deadlock in pty.spawn()
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