Fix issue where large stdin writes can cause Tornado to hang

.github/workflows/test.yml

@@ -101,6 +101,16 @@ jobs:
       - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
       - uses: jupyterlab/maintainer-tools/.github/actions/check-links@v1
 
+  jupyter_server_terminals:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v2
+      - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
+      - uses: jupyterlab/maintainer-tools/.github/actions/downstream-test@v1
+        with:
+          package_name: jupyter_server_terminals
+
   # Run "pre-commit run --all-files --hook-stage=manual"
   pre-commit:
     name: Run pre-commit hook

demos/custom_exec.py

@@ -0,0 +1,43 @@
+"""Using a custom thread pool for subprocess writes.
+"""
+from concurrent import futures
+
+import tornado.web
+
+# This demo requires tornado_xstatic and XStatic-term.js
+import tornado_xstatic
+from common_demo_stuff import STATIC_DIR, TEMPLATE_DIR, run_and_show_browser
+
+from terminado import SingleTermManager, TermSocket
+
+
+class TerminalPageHandler(tornado.web.RequestHandler):
+    def get(self):
+        return self.render(
+            "termpage.html",
+            static=self.static_url,
+            xstatic=self.application.settings["xstatic_url"],
+            ws_url_path="/websocket",
+        )
+
+
+def main(argv):
+    with futures.ThreadPoolExecutor(max_workers=2) as custom_exec:
+        term_manager = SingleTermManager(shell_command=["bash"], blocking_io_executor=custom_exec)
+        handlers = [
+            (r"/websocket", TermSocket, {"term_manager": term_manager}),
+            (r"/", TerminalPageHandler),
+            (r"/xstatic/(.*)", tornado_xstatic.XStaticFileHandler, {"allowed_modules": ["termjs"]}),
+        ]
+        app = tornado.web.Application(
+            handlers,
+            static_path=STATIC_DIR,
+            template_path=TEMPLATE_DIR,
+            xstatic_url=tornado_xstatic.url_maker("/xstatic/"),
+        )
+        app.listen(8765, "localhost")
+        run_and_show_browser("http://localhost:8765/", term_manager)
+
+
+if __name__ == "__main__":
+    main([])

terminado/management.py

@@ -14,6 +14,7 @@
 import signal
 import warnings
 from collections import deque
+from concurrent import futures
 
 try:
     from ptyprocess import PtyProcessUnicode
@@ -153,7 +154,13 @@ class TermManagerBase:
     """Base class for a terminal manager."""
 
     def __init__(
-        self, shell_command, server_url="", term_settings=None, extra_env=None, ioloop=None
+        self,
+        shell_command,
+        server_url="",
+        term_settings=None,
+        extra_env=None,
+        ioloop=None,
+        blocking_io_executor=None,
     ):
         self.shell_command = shell_command
         self.server_url = server_url
@@ -163,6 +170,13 @@ def __init__(
 
         self.ptys_by_fd = {}
 
+        if blocking_io_executor is None:
+            self._blocking_io_executor_is_external = False
+            self.blocking_io_executor = futures.ThreadPoolExecutor(max_workers=1)
+        else:
+            self._blocking_io_executor_is_external = True
+            self.blocking_io_executor = blocking_io_executor
+
         if ioloop is not None:
             warnings.warn(
                 f"Setting {self.__class__.__name__}.ioloop is deprecated and ignored",
@@ -259,6 +273,8 @@ def client_disconnected(self, websocket):
 
     async def shutdown(self):
         await self.kill_all()
+        if not self._blocking_io_executor_is_external:
+            self.blocking_io_executor.shutdown(wait=False, cancel_futures=True)
 
     async def kill_all(self):
         futures = []