context.py

# -*- coding: utf-8 -*-
# Copyright 2018 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Context for currently running tasks and transactions."""

import collections
import contextlib
import contextvars
import itertools
import os
import threading
import uuid

from google.cloud.ndb import _eventloop
from google.cloud.ndb import exceptions
from google.cloud.ndb import key as key_module


class _ContextIds:
    """Iterator which generates a sequence of context ids.

    Useful for debugging complicated interactions among concurrent processes and
    threads.

    Each value in the sequence is a string that include the machine's "node", acquired
    via `uuid.getnode()`, the current process id, and a sequence number which increases
    monotonically starting from one in each process. The combination of all three is
    sufficient to uniquely identify the context in which a particular piece of code is
    being run. Each context, as it is created, is assigned the next id in this sequence.
    The context id is used by `utils.logging_debug` to grant insight into where a debug
    logging statement is coming from in a cloud environment.
    """

    def __init__(self):
        self.prefix = "{}-{}-".format(uuid.getnode(), os.getpid())
        self.counter = itertools.count(1)
        self.lock = threading.Lock()

    def __next__(self):
        with self.lock:
            sequence_number = next(self.counter)

        return self.prefix + str(sequence_number)

    next = __next__  # Python 2.7


_context_ids = _ContextIds()


class _LocalState:
    """Thread local state."""

    def __init__(self):
        self._toplevel_context = contextvars.ContextVar(
            "_toplevel_context", default=None
        )
        self._context = contextvars.ContextVar("_context", default=None)

    @property
    def context(self):
        return self._context.get()

    @context.setter
    def context(self, value):
        self._context.set(value)

    @property
    def toplevel_context(self):
        return self._toplevel_context.get()

    @toplevel_context.setter
    def toplevel_context(self, value):
        self._toplevel_context.set(value)


_state = _LocalState()


def get_context(raise_context_error=True):
    """Get the current context.

    This function should be called within a context established by
    :meth:`google.cloud.ndb.client.Client.context`.

    Args:
        raise_context_error (bool): If set to :data:`True`, will raise an
            exception if called outside of a context. Set this to :data:`False`
            in order to have it just return :data:`None` if called outside of a
            context. Default: :data:`True`

    Returns:
        Context: The current context.

    Raises:
        .ContextError: If called outside of a context
            established by :meth:`google.cloud.ndb.client.Client.context` and
            ``raise_context_error`` is :data:`True`.
    """
    context = _state.context
    if context:
        return context

    if raise_context_error:
        raise exceptions.ContextError()


def get_toplevel_context(raise_context_error=True):
    """Get the current top level context.

    This function should be called within a context established by
    :meth:`google.cloud.ndb.client.Client.context`.

    The toplevel context is the context created by the call to
    :meth:`google.cloud.ndb.client.Client.context`. At times, this context will
    be superseded by subcontexts, which are used, for example, during
    transactions. This function will always return the top level context
    regardless of whether one of these subcontexts is the current one.

    Args:
        raise_context_error (bool): If set to :data:`True`, will raise an
            exception if called outside of a context. Set this to :data:`False`
            in order to have it just return :data:`None` if called outside of a
            context. Default: :data:`True`

    Returns:
        Context: The current context.

    Raises:
        .ContextError: If called outside of a context
            established by :meth:`google.cloud.ndb.client.Client.context` and
            ``raise_context_error`` is :data:`True`.
    """
    context = _state.toplevel_context
    if context:
        return context

    if raise_context_error:
        raise exceptions.ContextError()


def _default_policy(attr_name, value_type):
    """Factory for producing default policies.

    Born of the observation that all default policies are more less the
    same—they defer to some attribute on the model class for the key's kind and
    expects the value to be either of a particular type or a callable.

    Returns:
        Callable[[key], value_type]: A policy function suitable for use as a
            default policy.
    """
    # avoid circular imports on Python 2.7
    from google.cloud.ndb import model

    def policy(key):
        value = None
        if key is not None:
            kind = key.kind
            if callable(kind):
                kind = kind()
            modelclass = model.Model._kind_map.get(kind)
            if modelclass is not None:
                policy = getattr(modelclass, attr_name, None)
                if policy is not None:
                    if isinstance(policy, value_type):
                        value = policy
                    else:
                        value = policy(key)

        return value

    return policy


_default_cache_policy = _default_policy("_use_cache", bool)
"""The default cache policy.

Defers to ``_use_cache`` on the Model class for the key's kind.

See: :meth:`~google.cloud.ndb.context.Context.set_cache_policy`
"""

_default_global_cache_policy = _default_policy("_use_global_cache", bool)
"""The default global cache policy.

Defers to ``_use_global_cache`` on the Model class for the key's kind.

See: :meth:`~google.cloud.ndb.context.Context.set_global_cache_policy`
"""

_default_global_cache_timeout_policy = _default_policy("_global_cache_timeout", int)
"""The default global cache timeout policy.

Defers to ``_global_cache_timeout`` on the Model class for the key's kind.

See: :meth:`~google.cloud.ndb.context.Context.set_global_cache_timeout_policy`
"""

_default_datastore_policy = _default_policy("_use_datastore", bool)
"""The default datastore policy.

Defers to ``_use_datastore`` on the Model class for the key's kind.

See: :meth:`~google.cloud.ndb.context.Context.set_datastore_policy`
"""


_ContextTuple = collections.namedtuple(
    "_ContextTuple",
    [
        "id",
        "client",
        "namespace",
        "eventloop",
        "batches",
        "commit_batches",
        "transaction",
        "cache",
        "global_cache",
        "on_commit_callbacks",
        "transaction_complete_callbacks",
        "legacy_data",
    ],
)


class _Context(_ContextTuple):
    """Current runtime state.

    Instances of this class hold on to runtime state such as the current event
    loop, current transaction, etc. Instances are shallowly immutable, but
    contain references to data structures which are mutable, such as the event
    loop. A new context can be derived from an existing context using
    :meth:`new`.

    :class:`Context` is a subclass of :class:`_Context` which provides only
    publicly facing interface. The use of two classes is only to provide a
    distinction between public and private API.

    Arguments:
        client (client.Client): The NDB client for this context.
    """

    def __new__(
        cls,
        client,
        id=None,
        namespace=key_module.UNDEFINED,
        eventloop=None,
        batches=None,
        commit_batches=None,
        transaction=None,
        cache=None,
        cache_policy=None,
        global_cache=None,
        global_cache_policy=None,
        global_cache_timeout_policy=None,
        datastore_policy=None,
        on_commit_callbacks=None,
        transaction_complete_callbacks=None,
        legacy_data=True,
        retry=None,
        rpc_time=None,
        wait_time=None,
    ):
        # Prevent circular import in Python 2.7
        from google.cloud.ndb import _cache

        if id is None:
            id = next(_context_ids)

        if eventloop is None:
            eventloop = _eventloop.EventLoop()

        if batches is None:
            batches = {}

        if commit_batches is None:
            commit_batches = {}

        # Create a cache and, if an existing cache was passed into this
        # method, duplicate its entries.
        new_cache = _cache.ContextCache()
        if cache:
            new_cache.update(cache)

        context = super(_Context, cls).__new__(
            cls,
            id=id,
            client=client,
            namespace=namespace,
            eventloop=eventloop,
            batches=batches,
            commit_batches=commit_batches,
            transaction=transaction,
            cache=new_cache,
            global_cache=global_cache,
            on_commit_callbacks=on_commit_callbacks,
            transaction_complete_callbacks=transaction_complete_callbacks,
            legacy_data=legacy_data,
        )

        context.set_cache_policy(cache_policy)
        context.set_global_cache_policy(global_cache_policy)
        context.set_global_cache_timeout_policy(global_cache_timeout_policy)
        context.set_datastore_policy(datastore_policy)
        context.set_retry_state(retry)

        return context

    def new(self, **kwargs):
        """Create a new :class:`_Context` instance.

        New context will be the same as context except values from ``kwargs``
        will be substituted.
        """
        fields = self._fields + tuple(self.__dict__.keys())
        state = {
            name: getattr(self, name) for name in fields if not name.startswith("_")
        }
        state.update(kwargs)
        return type(self)(**state)

    @contextlib.contextmanager
    def use(self):
        """Use this context as the current context.

        This method returns a context manager for use with the ``with``
        statement. Code inside the ``with`` context will see this context as
        the current context.
        """
        prev_context = _state.context
        _state.context = self
        if not prev_context:
            _state.toplevel_context = self
            self.rpc_time = 0
            self.wait_time = 0
        try:
            yield self
        finally:
            if prev_context:
                prev_context.cache.update(self.cache)
            else:
                _state.toplevel_context = None
            _state.context = prev_context

    def _use_cache(self, key, options=None):
        """Return whether to use the context cache for this key."""
        flag = options.use_cache if options else None
        if flag is None:
            flag = self.cache_policy(key)
        if flag is None:
            flag = True
        return flag

    def _use_global_cache(self, key, options=None):
        """Return whether to use the global cache for this key."""
        if self.global_cache is None:
            return False

        flag = options.use_global_cache if options else None
        if flag is None:
            flag = self.global_cache_policy(key)
        if flag is None:
            flag = True
        return flag

    def _global_cache_timeout(self, key, options):
        """Return  global cache timeout (expiration) for this key."""
        timeout = None
        if options:
            timeout = options.global_cache_timeout
        if timeout is None:
            timeout = self.global_cache_timeout_policy(key)
        return timeout

    def _use_datastore(self, key, options=None):
        """Return whether to use the Datastore for this key."""
        flag = options.use_datastore if options else None
        if flag is None:
            flag = self.datastore_policy(key)
        if flag is None:
            flag = True
        return flag


class Context(_Context):
    """User management of cache and other policy."""

    def clear_cache(self):
        """Clears the in-memory cache.

        This does not affect global cache.
        """
        self.cache.clear()

    def flush(self):
        """Force any pending batch operations to go ahead and run."""
        self.eventloop.run()

    def get_namespace(self):
        """Return the current context namespace.

        If `namespace` isn't set on the context, the client's namespace will be
        returned.

        Returns:
            str: The namespace, or `None`.
        """
        if self.namespace is key_module.UNDEFINED:
            return self.client.namespace

        return self.namespace

    def get_cache_policy(self):
        """Return the current context cache policy function.

        Returns:
            Callable: A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns a ``bool`` indicating if it
                should be cached. May be :data:`None`.
        """
        return self.cache_policy

    def get_datastore_policy(self):
        """Return the current context datastore policy function.

        Returns:
            Callable: A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns a ``bool`` indicating if it
                should use the datastore. May be :data:`None`.
        """
        raise NotImplementedError

    def get_global_cache_policy(self):
        """Return the current global cache policy function.

        Returns:
            Callable: A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns a ``bool`` indicating if it
                should be cached. May be :data:`None`.
        """
        return self.global_cache_policy

    get_memcache_policy = get_global_cache_policy  # backwards compatibility

    def get_global_cache_timeout_policy(self):
        """Return the current policy function global cache timeout (expiration).

        Returns:
            Callable: A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns an ``int`` indicating the
                timeout, in seconds, for the key. ``0`` implies the default
                timeout. May be :data:`None`.
        """
        return self.global_cache_timeout_policy

    get_memcache_timeout_policy = get_global_cache_timeout_policy

    def set_cache_policy(self, policy):
        """Set the context cache policy function.

        Args:
            policy (Callable): A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns a ``bool`` indicating if it
                should be cached.  May be :data:`None`.
        """
        if policy is None:
            policy = _default_cache_policy

        elif isinstance(policy, bool):
            flag = policy

            def policy(key):
                return flag

        self.cache_policy = policy

    def set_datastore_policy(self, policy):
        """Set the context datastore policy function.

        Args:
            policy (Callable): A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns a ``bool`` indicating if it
                should use the datastore.  May be :data:`None`.
        """
        if policy is None:
            policy = _default_datastore_policy

        elif isinstance(policy, bool):
            flag = policy

            def policy(key):
                return flag

        self.datastore_policy = policy

    def set_global_cache_policy(self, policy):
        """Set the global cache policy function.

        Args:
            policy (Callable): A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns a ``bool`` indicating if it
                should be cached.  May be :data:`None`.
        """
        if policy is None:
            policy = _default_global_cache_policy

        elif isinstance(policy, bool):
            flag = policy

            def policy(key):
                return flag

        self.global_cache_policy = policy

    set_memcache_policy = set_global_cache_policy  # backwards compatibility

    def set_global_cache_timeout_policy(self, policy):
        """Set the policy function for global cache timeout (expiration).

        Args:
            policy (Callable): A function that accepts a
                :class:`~google.cloud.ndb.key.Key` instance as a single
                positional argument and returns an ``int`` indicating the
                timeout, in seconds, for the key. ``0`` implies the default
                timeout. May be :data:`None`.
        """
        if policy is None:
            policy = _default_global_cache_timeout_policy

        elif isinstance(policy, int):
            timeout = policy

            def policy(key):
                return timeout

        self.global_cache_timeout_policy = policy

    set_memcache_timeout_policy = set_global_cache_timeout_policy

    def get_retry_state(self):
        return self._retry

    def set_retry_state(self, state):
        self._retry = state

    def clear_retry_state(self):
        self._retry = None

    def call_on_commit(self, callback):
        """Call a callback upon successful commit of a transaction.

        If not in a transaction, the callback is called immediately.

        In a transaction, multiple callbacks may be registered and will be
        called once the transaction commits, in the order in which they
        were registered.  If the transaction fails, the callbacks will not
        be called.

        If the callback raises an exception, it bubbles up normally.  This
        means: If the callback is called immediately, any exception it
        raises will bubble up immediately.  If the call is postponed until
        commit, remaining callbacks will be skipped and the exception will
        bubble up through the transaction() call.  (However, the
        transaction is already committed at that point.)

        Args:
            callback (Callable): The callback function.
        """
        if self.in_transaction():
            self.on_commit_callbacks.append(callback)
        else:
            callback()

    def call_on_transaction_complete(self, callback):
        """Call a callback upon completion of a transaction.

        If not in a transaction, the callback is called immediately.

        In a transaction, multiple callbacks may be registered and will be called once
        the transaction completes, in the order in which they were registered. Callbacks
        are called regardless of whether transaction is committed or rolled back.

        If the callback raises an exception, it bubbles up normally.  This means: If the
        callback is called immediately, any exception it raises will bubble up
        immediately.  If the call is postponed until commit, remaining callbacks will be
        skipped and the exception will bubble up through the transaction() call.
        (However, the transaction is already committed or rolled back at that point.)

        Args:
            callback (Callable): The callback function.
        """
        if self.in_transaction():
            self.transaction_complete_callbacks.append(callback)
        else:
            callback()

    def in_transaction(self):
        """Get whether a transaction is currently active.

        Returns:
            bool: :data:`True` if currently in a transaction, otherwise
                :data:`False`.
        """
        return self.transaction is not None

    def in_retry(self):
        """Get whether we are already in a retry block.

        Returns:
            bool: :data:`True` if currently in a retry block, otherwise
                :data:`False`.
        """
        return self._retry is not None

    def memcache_add(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_cas(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_decr(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_delete(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_get(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_gets(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_incr(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_replace(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def memcache_set(self, *args, **kwargs):
        """Direct pass-through to memcache client. No longer implemented."""
        raise exceptions.NoLongerImplementedError()

    def urlfetch(self, *args, **kwargs):
        """Fetch a resource using HTTP. No longer implemented."""
        raise exceptions.NoLongerImplementedError()


class ContextOptions(object):
    def __init__(self, *args, **kwargs):
        raise exceptions.NoLongerImplementedError()


class TransactionOptions(object):
    NESTED = 1  # join=False
    MANDATORY = 2  # join=True
    ALLOWED = 3  # join=True
    INDEPENDENT = 4  # join=False

    _PROPAGATION = frozenset((NESTED, MANDATORY, ALLOWED, INDEPENDENT))
    _JOINABLE = frozenset((MANDATORY, ALLOWED))
    _INT_TO_NAME = {
        NESTED: "nested",
        MANDATORY: "mandatory",
        ALLOWED: "allowed",
        INDEPENDENT: "independent",
    }


class AutoBatcher(object):
    def __init__(self, *args, **kwargs):
        raise exceptions.NoLongerImplementedError()