Fix input thread busy-looping at 100% CPU when stdin reaches EOF

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Fixed
+
+- Fixed the input thread busy-looping at 100% CPU when stdin reaches EOF <!-- TODO: link issue/PR when filed -->
+
 ## [8.2.8] - 2026-06-30
 
 ### Fixed

src/textual/drivers/linux_driver.py

@@ -431,6 +431,8 @@ def run_input_thread(self) -> None:
         decode = utf8_decoder
         read = os.read
 
+        eof = False
+
         def process_selector_events(
             selector_events: list[tuple[selectors.SelectorKey, int]],
             final: bool = False,
@@ -442,11 +444,18 @@ def process_selector_events(
                 final: True if this is the last call.
 
             """
+            nonlocal eof
             for last, (_selector_key, mask) in loop_last(selector_events):
                 if mask & EVENT_READ:
-                    unicode_data = decode(read(fileno, 1024 * 4), final=final and last)
+                    raw_data = read(fileno, 1024 * 4)
+                    if not raw_data:
+                        # EOF. A selector reports it as permanently readable, so
+                        # stop selecting or this thread would busy-loop.
+                        eof = True
+                        break
+                    unicode_data = decode(raw_data, final=final and last)
                     if not unicode_data:
-                        # This can occur if the stdin is piped
+                        # Incomplete UTF-8 sequence.
                         break
                     for event in feed(unicode_data):
                         self.process_message(event)
@@ -456,6 +465,8 @@ def process_selector_events(
         try:
             while not self.exit_event.is_set():
                 process_selector_events(selector.select(0.1))
+                if eof:
+                    break
             selector.unregister(self.fileno)
             process_selector_events(selector.select(0.1), final=True)
 

src/textual/drivers/linux_inline_driver.py

@@ -134,6 +134,8 @@ def run_input_thread(self) -> None:
         decode = utf8_decoder
         read = os.read
 
+        eof = False
+
         def process_selector_events(
             selector_events: list[tuple[selectors.SelectorKey, int]],
             final: bool = False,
@@ -145,11 +147,18 @@ def process_selector_events(
                 final: True if this is the last call.
 
             """
+            nonlocal eof
             for last, (_selector_key, mask) in loop_last(selector_events):
                 if mask & EVENT_READ:
-                    unicode_data = decode(read(fileno, 1024 * 4), final=final and last)
+                    raw_data = read(fileno, 1024 * 4)
+                    if not raw_data:
+                        # EOF. A selector reports it as permanently readable, so
+                        # stop selecting or this thread would busy-loop.
+                        eof = True
+                        break
+                    unicode_data = decode(raw_data, final=final and last)
                     if not unicode_data:
-                        # This can occur if the stdin is piped
+                        # Incomplete UTF-8 sequence.
                         break
                     for event in feed(unicode_data):
                         if isinstance(event, events.CursorPosition):
@@ -165,6 +174,8 @@ def process_selector_events(
         try:
             while not self.exit_event.is_set():
                 process_selector_events(selector.select(0.1))
+                if eof:
+                    break
             selector.unregister(self.fileno)
             process_selector_events(selector.select(0.1), final=True)
 

tests/test_driver_input_eof.py

@@ -0,0 +1,73 @@
+"""Regression test for the input thread when stdin reaches end-of-file.
+
+A selector reports a file descriptor at EOF as readable, so `select()` returns
+immediately, forever. Unless the input thread notices the EOF and stops
+selecting, it busy-loops and pegs a CPU core for the life of the app.
+
+Asserting the thread returns is a deterministic stand-in for measuring CPU: a
+thread that has returned cannot busy-loop.
+"""
+
+import os
+import signal
+import sys
+import threading
+from typing import Iterator
+
+import pytest
+
+from textual.app import App
+from textual.driver import Driver
+
+if sys.platform == "win32":
+    pytest.skip("LinuxDriver/LinuxInlineDriver are POSIX only", allow_module_level=True)
+
+from textual.drivers.linux_driver import LinuxDriver
+from textual.drivers.linux_inline_driver import LinuxInlineDriver
+
+
+@pytest.fixture
+def eof_fileno() -> Iterator[int]:
+    """A file descriptor permanently at EOF, like stdin whose terminal is gone."""
+    read_fd, write_fd = os.pipe()
+    os.close(write_fd)
+    try:
+        yield read_fd
+    finally:
+        os.close(read_fd)
+
+
+@pytest.fixture
+def preserve_signal_handlers() -> Iterator[None]:
+    """Restore the handlers that `LinuxDriver.__init__` installs."""
+    saved = {
+        number: signal.getsignal(number) for number in (signal.SIGTSTP, signal.SIGCONT)
+    }
+    try:
+        yield
+    finally:
+        for number, handler in saved.items():
+            if handler is not None:
+                signal.signal(number, handler)
+
+
+@pytest.mark.parametrize("driver_class", [LinuxDriver, LinuxInlineDriver])
+async def test_input_thread_stops_on_stdin_eof(
+    driver_class: type[Driver],
+    eof_fileno: int,
+    preserve_signal_handlers: None,
+) -> None:
+    async with App().run_test() as pilot:
+        driver = driver_class(pilot.app)
+        driver.fileno = eof_fileno
+
+        thread = threading.Thread(target=driver.run_input_thread, daemon=True)
+        thread.start()
+        thread.join(timeout=5.0)
+        spinning = thread.is_alive()
+        if spinning:
+            # Stop the thread before the fixture closes the descriptor under it.
+            driver.exit_event.set()
+            thread.join(timeout=5.0)
+
+        assert not spinning, "input thread is busy-looping on a stdin that is at EOF"