content/diskcache/fanout.py

"Fanout cache automatically shards keys and values."

import itertools as it
import os.path as op
import sqlite3
import time

from .core import ENOVAL, DEFAULT_SETTINGS, Cache, Disk, Timeout
from .memo import memoize
from .persistent import Deque, Index


class FanoutCache(object):
    "Cache that shards keys and values."
    def __init__(self, directory, shards=8, timeout=0.010, disk=Disk,
                 **settings):
        """Initialize cache instance.

        :param str directory: cache directory
        :param int shards: number of shards to distribute writes
        :param float timeout: SQLite connection timeout
        :param disk: `Disk` instance for serialization
        :param settings: any of `DEFAULT_SETTINGS`

        """
        self._directory = directory
        self._count = shards
        default_size_limit = DEFAULT_SETTINGS['size_limit']
        size_limit = settings.pop('size_limit', default_size_limit) / shards
        self._shards = tuple(
            Cache(
                op.join(directory, '%03d' % num),
                timeout=timeout,
                disk=disk,
                size_limit=size_limit,
                **settings
            )
            for num in range(shards)
        )
        self._hash = self._shards[0].disk.hash
        self._deques = {}
        self._indexes = {}


    @property
    def directory(self):
        """Cache directory."""
        return self._directory


    def __getattr__(self, name):
        return getattr(self._shards[0], name)


    def set(self, key, value, expire=None, read=False, tag=None, retry=False):
        """Set `key` and `value` item in cache.

        When `read` is `True`, `value` should be a file-like object opened
        for reading in binary mode.

        If database timeout occurs then fails silently unless `retry` is set to
        `True` (default `False`).

        :param key: key for item
        :param value: value for item
        :param float expire: seconds until the key expires
            (default None, no expiry)
        :param bool read: read value as raw bytes from file (default False)
        :param str tag: text to associate with key (default None)
        :param bool retry: retry if database timeout expires (default False)
        :return: True if item was set

        """
        index = self._hash(key) % self._count
        set_func = self._shards[index].set

        while True:
            try:
                return set_func(key, value, expire, read, tag)
            except Timeout:
                if retry:
                    continue
                else:
                    return False


    def __setitem__(self, key, value):
        """Set `key` and `value` item in cache.

        Calls :func:`FanoutCache.set` internally with `retry` set to `True`.

        :param key: key for item
        :param value: value for item

        """
        self.set(key, value, retry=True)


    def add(self, key, value, expire=None, read=False, tag=None, retry=False):
        """Add `key` and `value` item to cache.

        Similar to `set`, but only add to cache if key not present.

        This operation is atomic. Only one concurrent add operation for given
        key from separate threads or processes will succeed.

        When `read` is `True`, `value` should be a file-like object opened
        for reading in binary mode.

        :param key: key for item
        :param value: value for item
        :param float expire: seconds until the key expires
            (default None, no expiry)
        :param bool read: read value as bytes from file (default False)
        :param str tag: text to associate with key (default None)
        :param bool retry: retry if database timeout expires (default False)
        :return: True if item was added

        """
        index = self._hash(key) % self._count
        add_func = self._shards[index].add

        while True:
            try:
                return add_func(key, value, expire, read, tag)
            except Timeout:
                if retry:
                    continue
                else:
                    return False


    def incr(self, key, delta=1, default=0, retry=False):
        """Increment value by delta for item with key.

        If key is missing and default is None then raise KeyError. Else if key
        is missing and default is not None then use default for value.

        Operation is atomic. All concurrent increment operations will be
        counted individually.

        Assumes value may be stored in a SQLite column. Most builds that target
        machines with 64-bit pointer widths will support 64-bit signed
        integers.

        :param key: key for item
        :param int delta: amount to increment (default 1)
        :param int default: value if key is missing (default 0)
        :param bool retry: retry if database timeout expires (default False)
        :return: new value for item on success else None
        :raises KeyError: if key is not found and default is None

        """
        index = self._hash(key) % self._count
        incr_func = self._shards[index].incr

        while True:
            try:
                return incr_func(key, delta, default)
            except Timeout:
                if retry:
                    continue
                else:
                    return None


    def decr(self, key, delta=1, default=0, retry=False):
        """Decrement value by delta for item with key.

        If key is missing and default is None then raise KeyError. Else if key
        is missing and default is not None then use default for value.

        Operation is atomic. All concurrent decrement operations will be
        counted individually.

        Unlike Memcached, negative values are supported. Value may be
        decremented below zero.

        Assumes value may be stored in a SQLite column. Most builds that target
        machines with 64-bit pointer widths will support 64-bit signed
        integers.

        :param key: key for item
        :param int delta: amount to decrement (default 1)
        :param int default: value if key is missing (default 0)
        :param bool retry: retry if database timeout expires (default False)
        :return: new value for item on success else None
        :raises KeyError: if key is not found and default is None

        """
        return self.incr(key, -delta, default, retry)


    def get(self, key, default=None, read=False, expire_time=False, tag=False,
            retry=False):
        """Retrieve value from cache. If `key` is missing, return `default`.

        If database timeout occurs then returns `default` unless `retry` is set
        to `True` (default `False`).

        :param key: key for item
        :param default: return value if key is missing (default None)
        :param bool read: if True, return file handle to value
            (default False)
        :param float expire_time: if True, return expire_time in tuple
            (default False)
        :param tag: if True, return tag in tuple (default False)
        :param bool retry: retry if database timeout expires (default False)
        :return: value for item if key is found else default

        """
        index = self._hash(key) % self._count
        get_func = self._shards[index].get

        while True:
            try:
                return get_func(
                    key, default=default, read=read, expire_time=expire_time,
                    tag=tag,
                )
            except (Timeout, sqlite3.OperationalError):
                if retry:
                    continue
                else:
                    return default


    def __getitem__(self, key):
        """Return corresponding value for `key` from cache.

        Calls :func:`FanoutCache.get` internally with `retry` set to `True`.

        :param key: key for item
        :return: value for item
        :raises KeyError: if key is not found

        """
        value = self.get(key, default=ENOVAL, retry=True)

        if value is ENOVAL:
            raise KeyError(key)

        return value


    def read(self, key):
        """Return file handle corresponding to `key` from cache.

        :param key: key for item
        :return: file open for reading in binary mode
        :raises KeyError: if key is not found

        """
        handle = self.get(key, default=ENOVAL, read=True, retry=True)
        if handle is ENOVAL:
            raise KeyError(key)
        return handle


    def __contains__(self, key):
        """Return `True` if `key` matching item is found in cache.

        :param key: key for item
        :return: True if key is found

        """
        index = self._hash(key) % self._count
        return key in self._shards[index]


    def pop(self, key, default=None, expire_time=False, tag=False,
            retry=False):
        """Remove corresponding item for `key` from cache and return value.

        If `key` is missing, return `default`.

        Operation is atomic. Concurrent operations will be serialized.

        :param key: key for item
        :param default: return value if key is missing (default None)
        :param float expire_time: if True, return expire_time in tuple
            (default False)
        :param tag: if True, return tag in tuple (default False)
        :param bool retry: retry if database timeout expires (default False)
        :return: value for item if key is found else default

        """
        index = self._hash(key) % self._count
        pop_func = self._shards[index].pop

        while True:
            try:
                return pop_func(
                    key, default=default, expire_time=expire_time, tag=tag,
                )
            except Timeout:
                if retry:
                    continue
                else:
                    return default


    def delete(self, key, retry=False):
        """Delete corresponding item for `key` from cache.

        Missing keys are ignored.

        If database timeout occurs then fails silently unless `retry` is set to
        `True` (default `False`).

        :param key: key for item
        :param bool retry: retry if database timeout expires (default False)
        :return: True if item was deleted

        """
        index = self._hash(key) % self._count
        del_func = self._shards[index].__delitem__

        while True:
            try:
                return del_func(key)
            except Timeout:
                if retry:
                    continue
                else:
                    return False
            except KeyError:
                return False


    def __delitem__(self, key):
        """Delete corresponding item for `key` from cache.

        Calls :func:`FanoutCache.delete` internally with `retry` set to `True`.

        :param key: key for item
        :raises KeyError: if key is not found

        """
        deleted = self.delete(key, retry=True)

        if not deleted:
            raise KeyError(key)


    memoize = memoize


    def check(self, fix=False):
        """Check database and file system consistency.

        Intended for use in testing and post-mortem error analysis.

        While checking the cache table for consistency, a writer lock is held
        on the database. The lock blocks other cache clients from writing to
        the database. For caches with many file references, the lock may be
        held for a long time. For example, local benchmarking shows that a
        cache with 1,000 file references takes ~60ms to check.

        :param bool fix: correct inconsistencies
        :return: list of warnings
        :raises Timeout: if database timeout expires

        """
        return sum((shard.check(fix=fix) for shard in self._shards), [])


    def expire(self):
        """Remove expired items from cache.

        :return: count of items removed

        """
        return self._remove('expire', args=(time.time(),))


    def create_tag_index(self):
        """Create tag index on cache database.

        It is better to initialize cache with `tag_index=True` than use this.

        :raises Timeout: if database timeout expires

        """
        for shard in self._shards:
            shard.create_tag_index()


    def drop_tag_index(self):
        """Drop tag index on cache database.

        :raises Timeout: if database timeout expires

        """
        for shard in self._shards:
            shard.drop_tag_index()


    def evict(self, tag):
        """Remove items with matching `tag` from cache.

        :param str tag: tag identifying items
        :return: count of items removed

        """
        return self._remove('evict', args=(tag,))


    def cull(self):
        """Cull items from cache until volume is less than size limit.

        :return: count of items removed

        """
        return self._remove('cull')


    def clear(self):
        """Remove all items from cache.

        :return: count of items removed

        """
        return self._remove('clear')


    def _remove(self, name, args=()):
        total = 0
        for shard in self._shards:
            method = getattr(shard, name)
            while True:
                try:
                    count = method(*args)
                    total += count
                except Timeout as timeout:
                    total += timeout.args[0]
                else:
                    break
        return total


    def stats(self, enable=True, reset=False):
        """Return cache statistics hits and misses.

        :param bool enable: enable collecting statistics (default True)
        :param bool reset: reset hits and misses to 0 (default False)
        :return: (hits, misses)

        """
        results = [shard.stats(enable, reset) for shard in self._shards]
        return (sum(result[0] for result in results),
                sum(result[1] for result in results))


    def volume(self):
        """Return estimated total size of cache on disk.

        :return: size in bytes

        """
        return sum(shard.volume() for shard in self._shards)


    def close(self):
        "Close database connection."
        for shard in self._shards:
            shard.close()
        self._deques.clear()
        self._indexes.clear()


    def __enter__(self):
        return self


    def __exit__(self, *exception):
        self.close()


    def __getstate__(self):
        return (self._directory, self._count, self.timeout, type(self.disk))


    def __setstate__(self, state):
        self.__init__(*state)


    def __iter__(self):
        "Iterate keys in cache including expired items."
        iterators = [iter(shard) for shard in self._shards]
        return it.chain.from_iterable(iterators)


    def __reversed__(self):
        "Reverse iterate keys in cache including expired items."
        iterators = [reversed(shard) for shard in self._shards]
        return it.chain.from_iterable(reversed(iterators))


    def __len__(self):
        "Count of items in cache including expired items."
        return sum(len(shard) for shard in self._shards)


    def reset(self, key, value=ENOVAL):
        """Reset `key` and `value` item from Settings table.

        If `value` is not given, it is reloaded from the Settings
        table. Otherwise, the Settings table is updated.

        Settings attributes on cache objects are lazy-loaded and
        read-only. Use `reset` to update the value.

        Settings with the ``sqlite_`` prefix correspond to SQLite
        pragmas. Updating the value will execute the corresponding PRAGMA
        statement.

        :param str key: Settings key for item
        :param value: value for item (optional)
        :return: updated value for item
        :raises Timeout: if database timeout expires

        """
        for shard in self._shards:
            while True:
                try:
                    result = shard.reset(key, value)
                except Timeout:
                    pass
                else:
                    break
        return result


    def deque(self, name):
        """Return Deque with given `name` in subdirectory.

        >>> cache = FanoutCache('/tmp/diskcache/fanoutcache')
        >>> deque = cache.deque('test')
        >>> deque.clear()
        >>> deque.extend('abc')
        >>> deque.popleft()
        'a'
        >>> deque.pop()
        'c'
        >>> len(deque)
        1

        :param str name: subdirectory name for Deque
        :return: Deque with given name

        """
        _deques = self._deques

        try:
            return _deques[name]
        except KeyError:
            parts = name.split('/')
            directory = op.join(self._directory, 'deque', *parts)
            temp = Deque(directory=directory)
            _deques[name] = temp
            return temp


    def index(self, name):
        """Return Index with given `name` in subdirectory.

        >>> cache = FanoutCache('/tmp/diskcache/fanoutcache')
        >>> index = cache.index('test')
        >>> index.clear()
        >>> index['abc'] = 123
        >>> index['def'] = 456
        >>> index['ghi'] = 789
        >>> index.popitem()
        ('ghi', 789)
        >>> del index['abc']
        >>> len(index)
        1
        >>> index['def']
        456

        :param str name: subdirectory name for Index
        :return: Index with given name

        """
        _indexes = self._indexes

        try:
            return _indexes[name]
        except KeyError:
            parts = name.split('/')
            directory = op.join(self._directory, 'index', *parts)
            temp = Index(directory)
            _indexes[name] = temp
            return temp