''' Provides the ``ServerSession`` class.
'''
from __future__ import absolute_import
import logging
log = logging.getLogger(__name__)
import time
from tornado import gen, locks
from ..util.tornado import yield_for_all_futures
from .callbacks import _DocumentCallbackGroup
[docs]def current_time():
'''Return the time in milliseconds since the epoch as a floating
point number.
'''
try:
# python >=3.3 only
return time.monotonic() * 1000
except:
# if your python is old, don't set your clock backward!
return time.time() * 1000
def _needs_document_lock(func):
'''Decorator that adds the necessary locking and post-processing
to manipulate the session's document. Expects to decorate a
method on ServerSession and transforms it into a coroutine
if it wasn't already.
'''
@gen.coroutine
def _needs_document_lock_wrapper(self, *args, **kwargs):
# while we wait for and hold the lock, prevent the session
# from being discarded. This avoids potential weirdness
# with the session vanishing in the middle of some async
# task.
if self.destroyed:
log.debug("Ignoring locked callback on already-destroyed session.")
raise gen.Return(None)
self.block_expiration()
try:
with (yield self._lock.acquire()):
if self._pending_writes is not None:
raise RuntimeError("internal class invariant violated: _pending_writes " + \
"should be None if lock is not held")
self._pending_writes = []
try:
result = yield yield_for_all_futures(func(self, *args, **kwargs))
finally:
# we want to be very sure we reset this or we'll
# keep hitting the RuntimeError above as soon as
# any callback goes wrong
pending_writes = self._pending_writes
self._pending_writes = None
for p in pending_writes:
yield p
raise gen.Return(result)
finally:
self.unblock_expiration()
return _needs_document_lock_wrapper
[docs]class ServerSession(object):
''' Hosts an application "instance" (an instantiated Document) for one or more connections.
'''
def __init__(self, session_id, document, io_loop=None):
if session_id is None:
raise ValueError("Sessions must have an id")
if document is None:
raise ValueError("Sessions must have a document")
self._id = session_id
self._document = document
self._loop = io_loop
self._subscribed_connections = set()
self._last_unsubscribe_time = current_time()
self._lock = locks.Lock()
self._current_patch_connection = None
self._document.on_change_dispatch_to(self)
self._callbacks = _DocumentCallbackGroup(io_loop)
self._pending_writes = None
self._destroyed = False
self._expiration_requested = False
self._expiration_blocked_count = 0
wrapped_callbacks = self._wrap_session_callbacks(self._document.session_callbacks)
self._callbacks.add_session_callbacks(wrapped_callbacks)
@property
def document(self):
return self._document
@property
def id(self):
return self._id
@property
def destroyed(self):
return self._destroyed
@property
def expiration_requested(self):
return self._expiration_requested
@property
def expiration_blocked(self):
return self._expiration_blocked_count > 0
@property
def expiration_blocked_count(self):
return self._expiration_blocked_count
def destroy(self):
self._destroyed = True
self._document.destroy(self)
del self._document
self._callbacks.remove_all_callbacks()
del self._callbacks
[docs] def request_expiration(self):
""" Used in test suite for now. Forces immediate expiration if no connections."""
self._expiration_requested = True
def block_expiration(self):
self._expiration_blocked_count += 1
def unblock_expiration(self):
if self._expiration_blocked_count <= 0:
raise RuntimeError("mismatched block_expiration / unblock_expiration")
self._expiration_blocked_count -= 1
[docs] def subscribe(self, connection):
"""This should only be called by ``ServerConnection.subscribe_session`` or our book-keeping will be broken"""
self._subscribed_connections.add(connection)
[docs] def unsubscribe(self, connection):
"""This should only be called by ``ServerConnection.unsubscribe_session`` or our book-keeping will be broken"""
self._subscribed_connections.discard(connection)
self._last_unsubscribe_time = current_time()
@property
def connection_count(self):
return len(self._subscribed_connections)
@property
def milliseconds_since_last_unsubscribe(self):
return current_time() - self._last_unsubscribe_time
@_needs_document_lock
def with_document_locked(self, func, *args, **kwargs):
''' Asynchronously locks the document and runs the function with it locked.'''
return func(*args, **kwargs)
def _wrap_document_callback(self, callback):
if getattr(callback, "nolock", False):
return callback
def wrapped_callback(*args, **kwargs):
return self.with_document_locked(callback, *args, **kwargs)
return wrapped_callback
def _wrap_session_callback(self, callback):
wrapped = self._wrap_document_callback(callback.callback)
return callback._copy_with_changed_callback(wrapped)
def _wrap_session_callbacks(self, callbacks):
wrapped = []
for cb in callbacks:
wrapped.append(self._wrap_session_callback(cb))
return wrapped
def _document_patched(self, event):
may_suppress = event.setter is self
if self._pending_writes is None:
raise RuntimeError("_pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes")
# TODO (havocp): our "change sync" protocol is flawed because if both
# sides change the same attribute at the same time, they will each end
# up with the state of the other and their final states will differ.
for connection in self._subscribed_connections:
if may_suppress and connection is self._current_patch_connection:
log.trace("Not sending notification back to client %r for a change it requested", connection)
else:
self._pending_writes.append(connection.send_patch_document(event))
@_needs_document_lock
def _handle_pull(self, message, connection):
log.debug("Sending pull-doc-reply from session %r", self.id)
return connection.protocol.create('PULL-DOC-REPLY', message.header['msgid'], self.document)
def _session_callback_added(self, event):
wrapped = self._wrap_session_callback(event.callback)
self._callbacks.add_session_callback(wrapped)
def _session_callback_removed(self, event):
self._callbacks.remove_session_callback(event.callback)
[docs] @classmethod
def pull(cls, message, connection):
''' Handle a PULL-DOC, return a Future with work to be scheduled. '''
return connection.session._handle_pull(message, connection)
@_needs_document_lock
def _handle_push(self, message, connection):
log.debug("pushing doc to session %r", self.id)
message.push_to_document(self.document)
return connection.ok(message)
[docs] @classmethod
def push(cls, message, connection):
''' Handle a PUSH-DOC, return a Future with work to be scheduled. '''
return connection.session._handle_push(message, connection)
@_needs_document_lock
def _handle_patch(self, message, connection):
self._current_patch_connection = connection
try:
message.apply_to_document(self.document, self)
finally:
self._current_patch_connection = None
return connection.ok(message)
@_needs_document_lock
def _handle_event(self, message, connection):
message.notify_event(self.document)
return connection.ok(message)
@classmethod
def event(cls, message, connection):
return connection.session._handle_event(message, connection)
[docs] @classmethod
def patch(cls, message, connection):
''' Handle a PATCH-DOC, return a Future with work to be scheduled. '''
return connection.session._handle_patch(message, connection)
