Source code for bokeh.server.session

#-----------------------------------------------------------------------------
# Copyright (c) 2012 - 2021, Anaconda, Inc., and Bokeh Contributors.
# All rights reserved.
#
# The full license is in the file LICENSE.txt, distributed with this software.
#-----------------------------------------------------------------------------
''' Provides the ``ServerSession`` class.

'''

#-----------------------------------------------------------------------------
# Boilerplate
#-----------------------------------------------------------------------------
from __future__ import annotations

import logging # isort:skip
log = logging.getLogger(__name__)

#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------

# Standard library imports
import inspect
import time
from copy import copy
from typing import (
    TYPE_CHECKING,
    Any,
    Awaitable,
    Callable,
    List,
    Set,
    TypeVar,
)

# External imports
from tornado import locks

if TYPE_CHECKING:
    from tornado.ioloop import IOLoop

# Bokeh imports
from ..util.token import generate_jwt_token
from .callbacks import DocumentCallbackGroup

if TYPE_CHECKING:
    from ..core.types import ID
    from ..document.document import Document
    from ..document.events import DocumentPatchedEvent
    from ..protocol import messages as msg
    from .callbacks import Callback, SessionCallback
    from .connection import ServerConnection

#-----------------------------------------------------------------------------
# Globals and constants
#-----------------------------------------------------------------------------

__all__ = (
    'current_time',
    'ServerSession',
)

#-----------------------------------------------------------------------------
# Private API
#-----------------------------------------------------------------------------

T = TypeVar("T")
F = TypeVar("F", bound=Callable[..., Any])

def _needs_document_lock(func: F) -> F:
    '''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.
    '''
    async def _needs_document_lock_wrapper(self: ServerSession, *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.")
            return None
        self.block_expiration()
        try:
            with await 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 = func(self, *args, **kwargs)
                    if inspect.isawaitable(result):
                        # Note that this must not be outside of the critical section.
                        # Otherwise, the async callback will be ran without document locking.
                        result = await result
                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:
                    await p
            return result
        finally:
            self.unblock_expiration()
    return _needs_document_lock_wrapper

#-----------------------------------------------------------------------------
# General API
#-----------------------------------------------------------------------------

[docs]def current_time() -> float: '''Return the time in milliseconds since the epoch as a floating point number. ''' return time.monotonic() * 1000
[docs]class ServerSession: ''' Hosts an application "instance" (an instantiated Document) for one or more connections. .. autoclasstoc:: ''' _subscribed_connections: Set[ServerConnection] _current_patch_connection: ServerConnection | None _pending_writes: List[Awaitable[None]] | None def __init__(self, session_id: ID, document: Document, io_loop: IOLoop | None = None, token: str | None = None) -> 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._token = token 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.callbacks.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_callback(cb) for cb in self._document.session_callbacks] self._callbacks.add_session_callbacks(wrapped_callbacks) @property def document(self) -> Document: return self._document @property def id(self) -> ID: return self._id @property def token(self) -> str: ''' A JWT token to authenticate the session. ''' if self._token: return self._token return generate_jwt_token(self.id) @property def destroyed(self) -> bool: return self._destroyed @property def expiration_requested(self) -> bool: return self._expiration_requested @property def expiration_blocked(self) -> bool: return self._expiration_blocked_count > 0 @property def expiration_blocked_count(self) -> int: return self._expiration_blocked_count def destroy(self) -> None: self._destroyed = True self._document.destroy(self) del self._document self._callbacks.remove_all_callbacks() del self._callbacks
[docs] def request_expiration(self) -> None: """ Used in test suite for now. Forces immediate expiration if no connections.""" self._expiration_requested = True
def block_expiration(self) -> None: self._expiration_blocked_count += 1 def unblock_expiration(self) -> None: if self._expiration_blocked_count <= 0: raise RuntimeError("mismatched block_expiration / unblock_expiration") self._expiration_blocked_count -= 1
[docs] def subscribe(self, connection: ServerConnection) -> None: """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: ServerConnection) -> None: """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) -> int: return len(self._subscribed_connections) @property def milliseconds_since_last_unsubscribe(self) -> float: return current_time() - self._last_unsubscribe_time @_needs_document_lock def with_document_locked(self, func: Callable[..., T], *args: Any, **kwargs: Any) -> T: ''' Asynchronously locks the document and runs the function with it locked.''' return func(*args, **kwargs) def _wrap_document_callback(self, callback: Callback) -> Callback: if getattr(callback, "nolock", False): return callback def wrapped_callback(*args: Any, **kwargs: Any): return self.with_document_locked(callback, *args, **kwargs) return wrapped_callback def _wrap_session_callback(self, callback: SessionCallback) -> SessionCallback: wrapped = copy(callback) wrapped._callback = self._wrap_document_callback(callback.callback) return wrapped def _document_patched(self, event: DocumentPatchedEvent) -> None: 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: continue self._pending_writes.append(connection.send_patch_document(event)) @_needs_document_lock def _handle_pull(self, message: msg.pull_doc_req, connection: ServerConnection) -> msg.pull_doc_reply: log.debug(f"Sending pull-doc-reply from session {self.id!r}") return connection.protocol.create('PULL-DOC-REPLY', message.header['msgid'], self.document) def _session_callback_added(self, event: SessionCallback): 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: msg.pull_doc_req, connection: ServerConnection) -> msg.pull_doc_reply: ''' 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: msg.push_doc, connection: ServerConnection) -> msg.ok: log.debug(f"pushing doc to session {self.id!r}") message.push_to_document(self.document) return connection.ok(message)
[docs] @classmethod def push(cls, message: msg.push_doc, connection: ServerConnection) -> msg.ok: ''' 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: msg.patch_doc, connection: ServerConnection) -> msg.ok: self._current_patch_connection = connection try: message.apply_to_document(self.document, self) finally: self._current_patch_connection = None return connection.ok(message)
[docs] @classmethod def patch(cls, message: msg.patch_doc, connection: ServerConnection) -> msg.ok: ''' Handle a PATCH-DOC, return a Future with work to be scheduled. ''' return connection.session._handle_patch(message, connection)
#----------------------------------------------------------------------------- # Dev API #----------------------------------------------------------------------------- #----------------------------------------------------------------------------- # Code #-----------------------------------------------------------------------------