paste / paste / reloader.py

# (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org)
# Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php
"""
A file monitor and server restarter.

Use this like:

..code-block:: Python

    import reloader
    reloader.install()

Then make sure your server is installed with a shell script like::

    err=3
    while test "$err" -eq 3 ; do
        python server.py
        err="$?"
    done

or is run from this .bat file (if you use Windows)::

    @echo off
    :repeat
        python server.py
    if %errorlevel% == 3 goto repeat

or run a monitoring process in Python (``paster serve --reload`` does
this).  

Use the ``watch_file(filename)`` function to cause a reload/restart for
other other non-Python files (e.g., configuration files).  If you have
a dynamic set of files that grows over time you can use something like::

    def watch_config_files():
        return CONFIG_FILE_CACHE.keys()
    paste.reloader.add_file_callback(watch_config_files)

Then every time the reloader polls files it will call
``watch_config_files`` and check all the filenames it returns.
"""

import os
import sys
import time
import threading
import traceback
from paste.util.classinstance import classinstancemethod

def install(poll_interval=1):
    """
    Install the reloading monitor.

    On some platforms server threads may not terminate when the main
    thread does, causing ports to remain open/locked.  The
    ``raise_keyboard_interrupt`` option creates a unignorable signal
    which causes the whole application to shut-down (rudely).
    """
    mon = Monitor(poll_interval=poll_interval)
    t = threading.Thread(target=mon.periodic_reload)
    t.setDaemon(True)
    t.start()

class Monitor(object):

    instances = []
    global_extra_files = []
    global_file_callbacks = []

    def __init__(self, poll_interval):
        self.module_mtimes = {}
        self.keep_running = True
        self.poll_interval = poll_interval
        self.extra_files = list(self.global_extra_files)
        self.instances.append(self)
        self.file_callbacks = list(self.global_file_callbacks)

    def periodic_reload(self):
        while True:
            if not self.check_reload():
                # use os._exit() here and not sys.exit() since within a
                # thread sys.exit() just closes the given thread and
                # won't kill the process; note os._exit does not call
                # any atexit callbacks, nor does it do finally blocks,
                # flush open files, etc.  In otherwords, it is rude.
                os._exit(3)
                break
            time.sleep(self.poll_interval)

    def check_reload(self):
        filenames = list(self.extra_files)
        for file_callback in self.file_callbacks:
            try:
                filenames.extend(file_callback())
            except:
                print >> sys.stderr, "Error calling paste.reloader callback %r:" % file_callback
                traceback.print_exc()
        for module in sys.modules.values():
            try:
                filename = module.__file__
            except (AttributeError, ImportError), exc:
                continue
            if filename is not None:
                filenames.append(filename)
        for filename in filenames:
            try:
                stat = os.stat(filename)
                if stat:
                    mtime = stat.st_mtime
                else:
                    mtime = 0
            except (OSError, IOError):
                continue
            if filename.endswith('.pyc') and os.path.exists(filename[:-1]):
                mtime = max(os.stat(filename[:-1]).st_mtime, mtime)
            elif filename.endswith('$py.class') and \
                    os.path.exists(filename[:-9] + '.py'):
                mtime = max(os.stat(filename[:-9] + '.py').st_mtime, mtime)
            if not self.module_mtimes.has_key(filename):
                self.module_mtimes[filename] = mtime
            elif self.module_mtimes[filename] < mtime:
                print >> sys.stderr, (
                    "%s changed; reloading..." % filename)
                return False
        return True

    def watch_file(self, cls, filename):
        """Watch the named file for changes"""
        filename = os.path.abspath(filename)
        if self is None:
            for instance in cls.instances:
                instance.watch_file(filename)
            cls.global_extra_files.append(filename)
        else:
            self.extra_files.append(filename)

    watch_file = classinstancemethod(watch_file)

    def add_file_callback(self, cls, callback):
        """Add a callback -- a function that takes no parameters -- that will
        return a list of filenames to watch for changes."""
        if self is None:
            for instance in cls.instances:
                instance.add_file_callback(callback)
            cls.global_file_callbacks.append(callback)
        else:
            self.file_callbacks.append(callback)

    add_file_callback = classinstancemethod(add_file_callback)

if sys.platform.startswith('java'):
    try:
        from _systemrestart import SystemRestart
    except ImportError:
        pass
    else:
        class JythonMonitor(Monitor):

            """
            Monitor that utilizes Jython's special
            ``_systemrestart.SystemRestart`` exception.

            When raised from the main thread it causes Jython to reload
            the interpreter in the existing Java process (avoiding
            startup time).

            Note that this functionality of Jython is experimental and
            may change in the future.
            """

            def periodic_reload(self):
                while True:
                    if not self.check_reload():
                        raise SystemRestart()
                    time.sleep(self.poll_interval)

watch_file = Monitor.watch_file
add_file_callback = Monitor.add_file_callback
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