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A custom thread class that extends threading.Thread with the ability to gracefully stop a Bokeh server running in the thread by stopping its IOLoop.

Purpose

StoppableThread provides a mechanism to run Bokeh server instances in separate threads with proper cleanup capabilities. It wraps the standard threading.Thread functionality and adds a stop() method that can gracefully shut down the Bokeh server and its associated Tornado IOLoop. This is particularly useful for managing Bokeh server lifecycles in applications that need to start and stop servers programmatically, such as in testing environments or dynamic server management scenarios.

Source Code

class StoppableThread(threading.Thread):
    """Thread class with a stop() method."""

    def __init__(self, io_loop=None, **kwargs):
        super().__init__(**kwargs)
        self.io_loop = io_loop

    def run(self):
        if hasattr(self, '_target'):
            target, args, kwargs = self._target, self._args, self._kwargs
        else:
            target, args, kwargs = self._Thread__target, self._Thread__args, self._Thread__kwargs
        if not target:
            return
        bokeh_server = None
        try:
            bokeh_server = target(*args, **kwargs)
        finally:
            if isinstance(bokeh_server, Server):
                bokeh_server.stop()
            if hasattr(self, '_target'):
                del self._target, self._args, self._kwargs
            else:
                del self._Thread__target, self._Thread__args, self._Thread__kwargs

    def stop(self):
        self.io_loop.add_callback(self.io_loop.stop)

Parameters

Parameter Details

io_loop: A Tornado IOLoop instance that will be used to stop the thread. This should be the same IOLoop that the Bokeh server is running on. If None, the stop() method will fail. This is typically obtained from the Bokeh Server instance.

**kwargs: Additional keyword arguments passed to the parent threading.Thread constructor. Common arguments include 'target' (the callable to run), 'args' (positional arguments for target), 'kwargs' (keyword arguments for target), 'name' (thread name), and 'daemon' (whether thread is a daemon).

Return Value

Instantiation returns a StoppableThread object that is a subclass of threading.Thread. The run() method returns None. The stop() method returns None but triggers the IOLoop to stop asynchronously via a callback.

Class Interface

Methods

Attributes

Dependencies

• threading
• bokeh
• tornado

Required Imports

import threading
from bokeh.server.server import Server
from tornado.ioloop import IOLoop

Usage Example

from tornado.ioloop import IOLoop
from bokeh.server.server import Server
from bokeh.application import Application

# Define a function that creates and returns a Bokeh server
def create_server():
    app = Application()
    io_loop = IOLoop.current()
    server = Server({'/': app}, io_loop=io_loop, port=5006)
    server.start()
    server.io_loop.start()
    return server

# Create and start the stoppable thread
io_loop = IOLoop()
thread = StoppableThread(io_loop=io_loop, target=create_server)
thread.start()

# Later, stop the thread gracefully
thread.stop()
thread.join()  # Wait for thread to finish

Best Practices

• Always provide an io_loop parameter during instantiation to enable the stop() method
• The target function should return a Bokeh Server instance for automatic cleanup
• Call thread.join() after stop() to ensure the thread has fully terminated before proceeding
• The thread automatically cleans up internal references to target, args, and kwargs after execution
• Handle both Python 3.10+ (_target) and older Python versions (_Thread__target) attribute naming
• The stop() method uses add_callback to ensure thread-safe stopping of the IOLoop
• If the target function doesn't return a Server instance, manual cleanup may be required
• Consider setting daemon=True if the thread should not prevent program exit

Tags

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